Spinal cord functional anatomy.

Review Article

Spinal Cord Functional Anatomy Tracey A. Cho, MD ABSTRACT Purpose of Review: This article reviews the neuroanatomical arrangement of the white matter pathways and gray matter columns of the spinal cord and explores how injury to the spinal cord leads to a typical constellation of symptoms and signs depending on the cross-sectional and longitudinal extent of the lesion. Recent Findings: As refined imaging techniques and novel biomarkers help identify spinal cord diseases more readily, familiarity with the classic spinal cord syndromes and localizing principles remains essential for prompt recognition of spinal cord involvement and efficient diagnostic testing in order to direct therapy and avoid permanent injury. Summary: Spinal cord disease can progress rapidly and cause debilitating deficits, making prompt recognition and treatment crucial. Knowledge of the organization of these pathways and cell columns, along with their surrounding structures and blood supply, allows the clinician to localize processes within the spinal column. This, in turn, can suggest the type of pathologic process involved and direct further evaluation and management.

Address correspondence to Dr Tracey A. Cho, Massachusetts General Hospital, Department of Neurology, 55 Fruit Street, Wang 835, Boston, MA 02114, [email protected]. Relationship Disclosure: Dr Cho has received compensation as a consultant for OptumInsight, Inc. Unlabeled Use of Products/Investigational Use Disclosure: Dr Cho reports no disclosure. * 2015, American Academy of Neurology.

Continuum (Minneap Minn) 2015;21(1):13–35.

INTRODUCTION The spinal cord serves as the conduit for information traveling between the brain and the periphery. While some additional processing occurs within the spinal cord, most of the volume of the spinal cord consists of these ascending and descending signals. Thus, pathologic processes affecting the spinal cord, even those limited to a small area, are usually clinically apparent. Knowledge of the organization of the pathways and cell columns within the spinal cord, along with their surrounding structures and blood supply, allows the clinician to localize processes within the spinal column. This, in turn, can suggest the type of pathologic process involved and direct further evaluation and management. While most of the articles in this issue address the specific disease processes that can affect the spinal cord, this article will review the Continuum (Minneap Minn) 2015;21(1):13–35

clinical symptoms and signs associated with particular spinal cord syndromes. LONGITUDINAL ORGANIZATION AND SURROUNDING STRUCTURES There are 31 spinal cord segments (eight cervical, one thoracic, five lumbar, five sacral, and one coccygeal) (Figure 1-11). Except for C1, which has no sensory nerve root, each segment has a pair of dorsal (sensory) and ventral (motor) roots that join to form a mixed spinal nerve just as they enter the dural sleeve and neural foramina. Each segment corresponds to a vertebra, except for C8, which has no corresponding vertebra. By convention, spinal nerves in the cervical region exit above their corresponding vertebra, with the C1 spinal nerves exiting between the C1 vertebra and the skull. Because C8 has no corresponding vertebra, C8 exits above T1. Starting with T1, the spinal nerves exit below their corresponding www.ContinuumJournal.com

Copyright © American Academy of Neurology. Unauthorized reproduction of this article is prohibited.

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Spinal Cord Functional Anatomy

FIGURE 1-1

Relation of vertebral bodies to spinal cord and spinal roots. Bolded terms refer to specific regions. Reprinted from Moore KL, et al, Wolters Kluwer/Lippincott Williams & Wilkins.1 B 2014 Lippincott Williams & Wilkins.

vertebra. During embryonic development, the vertebral column grows more rapidly than the spinal cord. At birth, the newborn spinal cord ends around the level of the L3 vertebral body and by 2 months of age has reached the adult position at the L1-L2 vertebral level, resulting in a pattern whereby successively more caudal spinal nerves must

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travel farther to reach their exit. The rostral spinal cervical nerves exit horizontally at the level of their corresponding vertebral body; the lower cervical and upper thoracic nerves travel obliquely one to two segments to reach their exit; and the lumbosacral nerves travel several segments vertically, forming the cauda equina with caudal-most nerves situated centrally.

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The thin, fragile spinal cord is protected by the vertebral column, which also serves to maintain the posture of the body. Each vertebra has a central ovoid body providing the bulk of the structural support. An arch of paired pedicles and laminae branches off the body and joins posteriorly to form the borders of the spinal canal, which surrounds the spinal cord. Each pedicle has a superior and an inferior notch, which form the exit site for spinal nerves (intervertebral or neural foramina). Three processes (one spinal and two transverse) provide attachment sites for spinal muscles. Each vertebra is connected to the vertebra above by superior processes and below by inferior processes, which help to determine the range of motion of the column. Between each vertebral body is an intervertebral disk, which serves to cushion the vertebral column while providing added flexibility (Figure 1-21). The vertebral column is bound together by several longitudinal ligaments and muscle attachments. The posterior longitudinal ligament runs along the posterior aspect of the vertebral bodies and intervertebral disks, forming the anterior wall of the spinal canal and helping to contain the intervertebral disks as they degenerate.1 In the cervical region, the posterior longitudinal ligament tends to constrain disk bulges from protruding centrally and instead directs disks laterally toward the neural foramen. Loss of disk height and the mechanical strain of flexion and extension over time, however, can lead to posterior ligament hypertrophy and joint osteophyte formation, contributing to central canal narrowing and cervical spondylotic myelopathy. For more information on cervical spondylotic and other degenerative causes of myelopathies, refer to the article ‘‘Myelopathy Due to Degenerative and Structural Spine Diseases’’ by Jinny O. Tavee, MD, and Kerry Continuum (Minneap Minn) 2015;21(1):13–35

H. Levin, MD, FAAN, in this issue . of Paired ligamenta flava connect the lamina of each vertebra with the laminae of the vertebrae above and below. Often referred to collectively as the ligamentum flavum, these elastic fibers form the posterior wall of the spinal canal. Like the posterior longitudinal ligament, the ligamentum flavum can hypertrophy over time, narrowing the central canal. In the cervical region, the ligamentum flavum can buckle inward dynamically with extension, further contributing to cervical spondylotic myelopathy. As in the cranium, three layers of meninges surround the spinal cord for its entire length. The cranial dura consists of two tightly adherent layers, and the cranial epidural space is bound by periosteum outwardly and the two-layered

FIGURE 1-2

KEY POINT

h In the cervical region, the ligamentum flavum can buckle inward dynamically with extension, further contributing to cervical spondylotic myelopathy.

Vertebral body anatomy (A) and relation to intervertebral disks and neural foramen (B). Modified from Moore KL, et al, Wolters Kluwer/ Lippincott Williams & Wilkins.1 B 2014 Lippincott Williams & Wilkins.



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Spinal Cord Functional Anatomy KEY POINTS

h The spinal epidural space contains veins and fatty tissue, which serves as a useful landmark on MRI.

h While the posterior spinal artery receives flow from 10 to 16 posterior radicular branches, the anterior spinal artery has fewer, but larger, anterior radicular arteries feeding into it, making the anterior spinal artery distribution more prone to clinically apparent embolic or thrombotic infarction.

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dura inwardly. In the spinal canal (beginning at the foramen magnum), the periosteal dural layer separates from the inner layer, creating an anatomical epidural space between the two layers. The spinal epidural space contains veins and fatty tissue, which serves as a useful landmark on MRI. Additionally, anesthesia can be used in the spinal epidural space for a segmental or regional block. The inner dura, or thecal sac, encloses the arachnoid, CSF, pia, and spinal cord from the foramen magnum rostrally to the second sacral level caudally. As each spinal nerve exits the spinal canal in the neural foramen, it passes through a dural sleeve investing the nerve components. Attached to the dura is the arachnoid with CSF in the subarachnoid space. The pia is attached to the surface of the spinal cord, forming the internal boundary of the CSF (subarachnoid) space. The spinal cord is anchored rostrally by the cervicomedullary junction and caudally by the filum terminale (an extension of the pia at the conus medullaris, which attaches to the first coccygeal segment through the sacral dura). The spinal cord is enlarged in the cervical and lumbar regions due to the large volume of motor neurons dedicated to finely tuned movements in the upper (cervical) and lower (lumbar) extremities. These areas are also the points in the vertebral column where the most range of motion occurs and, therefore, are prone to degenerative changes (eg, loss of disk height, disk protrusion, ligament hypertrophy, and osteophyte formation). An anterior and posterior system provides the blood supply to the spinal cord. A single anterior spinal artery runs the length of the cord in the deep anterior median fissure, and paired posterior spinal arteries run in the dorsolateral sulci, where the dorsal nerve roots attach. The anterior spinal artery supplies the anterior two-thirds of the spinal

cord while the posterior spinal arteries serve the posterior third (primarily posterior columns). The anterior and posterior spinal arteries originate from descending branches of the vertebral arteries in the neck. The spinal arteries are further fed by segmental radicular arteries, which branch off the vertebral arteries in the cervical region, intercostal branches of the aorta in the midthoracic region, and the great radicular artery (of Adamkiewicz) in the lower thoracic or lumbar region. While the posterior spinal artery receives flow from 10 to 16 posterior radicular branches, the anterior spinal artery has fewer, but larger, anterior radicular arteries feeding into it, making the anterior spinal artery distribution more prone to clinically apparent embolic or thrombotic infarction. In addition, the area between these larger segmental anterior radicular arteries constitutes the region most theoretically vulnerable to hypoperfusion, which is the midthoracic region in most people. However, the clinical relevance of this border zone is ambiguous as this region is not reliably involved in hypoperfused states. The venous drainage of the spinal cord feeds into a longitudinal anterior and longitudinal posterior vein, with a pial plexus around the spinal cord connecting them. Radicular veins drain from the pial plexus into the circumferential and longitudinal epidural plexus. This rich, valveless network serves as a conduit for the hematogenous spread of neoplastic metastases and infectious pathogens, which can seed the spinal epidural space. For more information on the vascular anatomy of the spinal cord, refer to the article ‘‘Vascular Myelopathies’’ by Alejandro A. Rabinstein, MD, FAAN, in . this issue of CROSS-SECTIONAL ANATOMY The spinal cord consists of longitudinal columns of nuclei (gray matter)



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KEY POINT

h The anterior horn is organized somatotopically; the neurons controlling the axial uscles are most medially placed, the neurons controlling the proximal limb muscles lie in between, and the neurons serving the fine motor control of the distal limbs are most laterally placed.

FIGURE 1-3

Gray and white matter divisions of the spinal cord.

surrounded by ascending and descending tracts (white matter) (Figure 1-3). The butterfly, or H-shaped, gray matter is divided into posterior (dorsal), anterior (ventral), and lateral (intermediate) horns. The gray matter horns divide the white matter into posterior, lateral, and anterior columns (also referred to as funiculi). A remnant of the neural tube central cavity, the central canal is typically a closed space that runs the length of the spinal cord, beginning rostrally from the fourth ventricle. The central canal lies in the center of the gray matter, is lined with ependyma, filled with CSF, and surrounded by glial cells. Gray Matter Columns The anterior horn contains alpha and gamma (lower) motor neurons as well as interneurons that help to fine-tune the motor output. The anterior horn is organized somatotopically; the neurons controlling the axial muscles are most medially placed, the neurons controlling the proximal limb muscles lie in between, and the neurons serving the fine motor control of the distal limbs are Continuum (Minneap Minn) 2015;21(1):13–35

most laterally placed. The motor neurons are also organized by function, with neurons serving extensor muscles lying ventral to those controlling flexors. The posterior horn contains secondary sensory neurons and interneurons receiving input from the dorsal root ganglia (primary sensory neurons). These neurons are organized in layers based on synaptic inputs and outputs. The outermost layers serve exteroceptive (superficial) sensations including pain, temperature, and light touch, and their outputs form the contralateral spinothalamic tracts. The deeper layers receive inputs on unconscious proprioceptive (deep) sensation and contribute to the ipsilateral spinocerebellar tracts as well as participate in local reflex arcs. The intermediolateral cell column in the lateral horn from C8 to L3 contains sympathetic autonomic nuclei that receive inputs from the hypothalamus, and these ‘‘preganglionic’’ sympathetic neurons send outputs via the ventral roots to the sympathetic chain ganglia. From S2 to S4 the parasympathetic ‘‘preganglionic’’ nuclei are situated in www.ContinuumJournal.com


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Spinal Cord Functional Anatomy KEY POINT

h The most prominent ascending tracts are the spinothalamic tract (pain, temperature, and crude touch) and the pathway made up of the posterior columnYmedial lemniscus (vibration, proprioception, and fine touch).

the intermediate cell column, similarly exit via the ventral roots, and then pass to end organ ganglia in the pelvis. Finally, the posterior thoracic nucleus, medially situated between anterior and posterior horns, receives unconscious proprioception inputs from the posterior column collaterals and send secondary axons to the cerebellum in the spinocerebellar tracts. White Matter Tracts The gray matter divides the white matter of the spinal cord into three columns: posterior, lateral, and anterior (Figure 1-3). The white matter bundles may be classified as ascending or descending. The most prominent ascending tracts are the spinothalamic tract (pain, temperature, and crude touch) and the pathway made up of the posterior columnYmedial lemniscus (vibration, proprioception, and fine touch). See Table 1-1 for details on other ascending pathways. The primary sensory neurons in the dorsal root ganglia have pseudounipolar axons, with one process transmitting sensory input from the tissues to the cell body and another transmitting signals from the cell body to the spinal cord. In general, the sensory pathways synapse ipsilaterally before crossing to the contralateral side. The spinothalamic tract, along with several other clinically insignificant tracts, constitute the anterolateral system, in which the initial synapse occurs in the dorsal horn gray matter. Second-order neurons then send axons across the anterior commissure (anterior to the central canal) to ascend in the contralateral anterolateral pathway. This decussation usually takes two to three segments, so that lesions affecting the anterolateral tract at a given spinal cord level will have a contralateral sensory deficit two to three levels lower. The proximity of the crossing spinothalamic fibers in the anterior commis-

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sure leads to early deficits in pain and temperature when syringomyelia adjacent to the central canal compresses the anterior commissure. The spinothalamic tract in the anterolateral system is arranged somatotopically, with sacral fibers most lateral and cervical fibers most medial. This arrangement accounts for the phenomenon of sacral sparing, in which a large central cord lesion may spare the outermost sacral fibers and, thus, spare sensation in the lower sacral dermatomes. Spinothalamic fibers ascend to the thalamic ventral posterolateral (VPL) nucleus (Table 1-1). Unlike the anterolateral pathway, fibers entering the posterior column system ascend the entire length of the spinal cord before synapsing with second-order neurons in the medulla. The posterior columns enlarge rostrally as more fibers are added, and two distinct columns form in the upper thoracic and cervical cord. Axons carrying vibration and proprioception (conscious and unconscious) from the lower extremities and lower trunk enter the ipsilateral gracile fasciculus medially, while fibers from the upper extremities and neck are added on laterally to form the cuneate fasciculus. Both gracile and cuneate pathways synapse in the medulla, where second-order neurons in their respective nuclei finally send projections across the midline via internal arcuate fibers to the contralateral medial lemniscus and then to the thalamic VPL nucleus. Thus, between the medulla and any given level of the spinal cord, the fibers of the anterolateral system and posterior columns are dissociated, with the anterolateral fibers crossing immediately to travel in the contralateral cord and the posterior columns remaining ipsilateral until reaching the medulla. In addition to the anterolateral and posterior column systems, several other tracts ascend the spinal cord with variable clinical relevance. Unconscious



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TABLE 1-1

Ascending Spinal Cord Tracts

Tract

Origin

Decussation

Location in Cord Terminus

Function

Medulla (internal arcuate)

Posterior column (medial)

Thalamic ventral posterolateral nucleus

Fine touch Vibration Proprioception (lower body)

Medulla (internal arcuate)

Posterior column (lateral)


Fine touch Vibration Proprioception (upper body)

Anterior commissure

Lateral, anterior columns


Crude touch Pain Temperature

Mostly uncrossed

Lateral column

Medullary reticular system

Behavioral response to pain, arousal

Spinomesencephalic Dorsal horn tract

Anterior commissure

Lateral column

Periaqueductal gray

Central modulation of pain

Spinotectal tract

Dorsal horn

Anterior commissure

Lateral column

Superior colliculus Turn head, eyes toward painful stimulus

Spinohypothalamic tract

Dorsal horn

Anterior commissure

Lateral column

Hypothalamus

Autonomic response to pain

Uncrossed

Posterior column (first order); lateral column (second order)

Ipsilateral cerebellum

Unconscious proprioception (lower body)

Posterior (Dorsal) Columns Gracile fasciculusa Dorsal root ganglion

Cuneate fasciculusa

Dorsal root ganglion

Anterolateral System Spinothalamic tracta Dorsal horn

Spinoreticular tract

Dorsal horn

Spinocerebellar Tracts Posterior (dorsal) Thoracic spinocerebellar posterior tract (Clarke) nucleus Cuneocerebellar tract (located in medulla)

Accessory cuneate (medulla)

Uncrossed

Posterior column (first order); lateral medulla (second order)


Unconscious proprioception (upper limb, head)

Anterior (ventral) spinocerebellar tract

Dorsal horn

Anterior commissure, cerebellum

Lateral column


Unconscious proprioception (lower body)

Spino-olivary tract

Dorsal horn

Anterior commissure



Unconscious proprioception

Uncrossed

Lateral column


Unconscious proprioception (upper limb, head)

Dorsal horn Rostral spinocerebellar tract (joins anterior spinocerebellar tract) a

Most relevant for clinical localization.

proprioception information from the lower extremities and lower trunk travels alongside conscious propriocepContinuum (Minneap Minn) 2015;21(1):13–35

tion in the gracile fasciculus, before collateral fibers exit to synapse on the thoracic posterior (Clarke) nucleus. www.ContinuumJournal.com


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Spinal Cord Functional Anatomy KEY POINTS

h Between the medulla and any given level of the spinal cord, the fibers of the anterolateral system and posterior columns are dissociated, with the anterolateral fibers crossing within one to two levels of entering the spinal cord to travel in the contralateral cord and the posterior columns remaining ipsilateral until reaching the medulla.

h The somatotopic organization of the lateral corticospinal tract accounts for the early involvement of lower extremity corticospinal function in compressive cervical lesions.

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Secondary neurons send fibers through the ipsilateral posterior spinocerebellar tracts to the cerebellum via the inferior cerebellar peduncle. Analogous collaterals carrying upper extremity and trunk unconscious proprioception exit the cuneate fasciculus to synapse in the medullary accessory cuneate nucleus, which sends signals to the ipsilateral inferior cerebellar peduncle (Table 1-1). The most prominent descending tract is the corticospinal (pyramidal) tract, often referred to as a long tract due to its uninterrupted passage from the primary motor cortex in the precentral gyrus to the anterior horn. Almost all of the descending motor fibers cross in the caudal medulla to form the lateral corticospinal tract. The few remaining uncrossed fibers form the anterior corticospinal tract, which cross at the level of synapse to anterior horn cells and are primarily involved in axial and proximal limb (girdle) motor control. Within the lateral corticospinal tract, fibers synapsing in more rostral (cervical) areas are situated medially and fibers synapsing to caudal (sacral) regions are situated laterally. This arrangement may account for the early involvement of lower extremity corticospinal function in compressive cervical lesions. Several other less well-defined tracts descend through the spinal cord (Table 1-2). Adjacent to the lateral corticospinal tract in the lateral cord, the rubrospinal tract has an unclear role in humans but may be responsible for upper extremity flexor movements in animals with lesions above the red nucleus (ie, decorticate posturing).2 In the anterior descending motor column, the vestibulospinal, reticulospinal, and tectospinal tracts descend along with the anterior corticospinal tract.3 The clinical significance of these tracts in humans is overshadowed by the dominant role of the lateral corticospinal

tract in controlling fine motor movements, but in general, the medial descending motor systems aid in the control of axial muscles, posture, balance, and head movements. It is postulated that these spinal ‘‘extrapyramidal’’ motor systems evolved to coordinate an organism’s stride with minimal conscious input, while the pyramidal system developed to finely tune more complex movements using the hands and feet. The autonomic fibers constitute another important descending system. While the lateral corticospinal tract is densely packed and grossly identified on cord sections, the descending autonomic fibers travel more diffusely in the lateral aspect of the cord adjacent to the lateral horn, but without a well-defined tract (Figure 1-4). Direct and indirect supranuclear autonomic inputs arise from the hypothalamus as well as the insula and amygdala, among other limbic and brainstem centers. For the sympathetic system, these supranuclear signals pass laterally through the brainstem and spinal cord and synapse in the ipsilateral intermediolateral cell column in the thoracic and upper lumbar cord. These preganglionic neurons then send outputs via the ventral spinal roots to either paravertebral sympathetic ganglia or to prevertebral ganglia proximate to end organs. The parasympathetic nuclei lie in the brainstem and lateral gray matter in the S2 to S4 segments. Efferent preganglionic parasympathetic fibers exit the spinal cord via ventral roots and travel in the ventral ramus to the end organs, where they synapse on postganglionic neurons. The control of bladder function involves complex interactions between somatosensory, somatomotor, parasympathetic, and sympathetic systems and serves as an important clinical indicator of spinal cord function. In healthy adults, bladder function is under voluntary



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TABLE 1-2

Descending Spinal Cord Tracts

Tract

Origin

Decussation

Location in Cord

Terminus

Function

Lateral corticospinal (pyramidal)a

Primary motor cortex

Caudal medulla

Lateral column

Contralateral anterior horn throughout cord

Control of contralateral muscles

Anterior (ventral) corticospinal

Primary motor cortex

Level of synapse

Anterior column

Contralateral cervical and upper thoracic anterior horn

Control of contralateral axial and girdle muscles

Rubrospinal

Red nucleus

Ventral midbrain

Lateral column (anterior to lateral corticospinal tract)

Cervical interneurons

Control of contralateral muscles (especially flexor)b

Vestibulospinal Vestibular nuclei

Medulla for medial tract, otherwise uncrossed

Anterior column

Ipsilateral and contralateral interneurons

Head and neck position, balance, center of gravity

Reticulospinal

Pontine and medullary reticular formation

Uncrossed


Ipsilateral interneurons

Contribute to automatic posture and gait control

Tectospinal

Superior colliculus

Dorsal midbrain

Anterior column

Contralateral interneurons in cervical cord

Reflex head movement to visual, auditory, sensory stimulib

Descending autonomic fibersa

Hypothalamus, brainstem nuclei

None

Lateral columnc

Ipsilateral thoracic sympathetic, sacral parasympathetic neurons

Autonomic outputs

a b c

Most relevant for clinical localization. Function unclear in humans. Poorly defined (diffuse) tract.

control. Sensory input from the bladder and urethra passes through the S2 to S4 nerve roots and via the anterolateral system and posterior columns to frontal and pontine micturition centers. The frontal micturition center (medial frontal region) triggers the pontine micturition center (locus caeruleus) to initiate the voiding reflex. The somatic motor neurons in the medial anterior horns of S2 to S4 control the pelvic floor muscles, Continuum (Minneap Minn) 2015;21(1):13–35

and specialized motor neurons in the lateral part of the S2 to S4 anterior horns, called the Onuf nucleus, serve voluntary control of the urethral (and anal) sphincter. Sympathetic inputs from the intermediolateral cell column in the T11 to L2 region supply a small component of muscle in the bladder neck. Parasympathetic motor neurons in the lateral horn of S2 to S4 activate the bladder detrusor muscle, which is the primary www.ContinuumJournal.com


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FIGURE 1-4

KEY POINTS

h The control of bladder function involves complex interactions between somatosensory, somatomotor, parasympathetic, and sympathetic systems and serves as an important clinical indicator of spinal cord function.

h Generally, cord lesions must be bilateral to impact bladder function, as well as bowel and sexual function.

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Principle white matter tracts of the spinal cord.

muscle responsible for voiding. When the pontine micturition center signals the voluntary somatic relaxation of the urethral sphincter, reflex inhibition of sympathetic bladder neck contraction occurs, along with activation of the parasympathetic detrusor contraction. This cascade is further stimulated by the flow of urine, and once urine flow stops, a urethral reflex triggers sphincter contraction. The parasympathetic system is the dominant driver of autonomic bladder control. Isolated lesions to the sympathetic fibers have less of an impact on bladder dysfunction, and, generally, spinal cord lesions must be bilateral to impact bladder function, as well as bowel and sexual function. A spinal cord lesion above S2 that disrupts descending somatic and voluntary pathways will cause an initial hypotonic (flaccid) bladder with reflex contraction of the urethral sphincter. The bladder will retain urine and eventually may have some overflow incontinence. This is analogous to ‘‘spinal shock,’’ in which weakness from a spinal cord injury is initially flaccid. Over weeks to months,

lesions in the spinal cord above S2 will cause a hypertonic (spastic bladder) in which the disinhibited detrusor may contract or spasm in response to small amounts of bladder filling. The reflex pathway between detrusor and sphincter also may become incoordinated, and the urethral sphincter may spasm, preventing complete voiding. This combination leads to urinary frequency, urinary urgency, or urge incontinence, and is often referred to as a neurogenic bladder. By contrast, lesions at S2 to S4 or their roots disrupt both somatic and parasympathetic motor inputs to detrusor and sphincter muscles, as well as afferent information about bladder filling. This tends to cause a persistent hypotonic bladder and a hypotonic sphincter, leading to urinary retention and overflow incontinence.4 Spinal cord lesions disrupting descending autonomic inputs also affect bowel, sexual, and cardiovascular functions. Constipation may result from lesions anywhere in the spinal cord. Spinal cord lesions above S2 cause an acutely flaccid anal sphincter, followed by the development of spastic sphincter contraction,



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which further contributes to constipation. Lesions at S2 to S4 or peripherally will cause both loss of anal tone and decreased intestinal motility below the splenic flexure. Thus, constipation predominates in chronic spinal cord injuries, but fecal incontinence may also be a problem. Sexual dysfunction may occur in men and women from spinal cord injuries at any level. Lesions (usually severe and acute) above T6 may lead to a phenomenon of autonomic dysreflexia. A stimulus, either noxious or non-noxious, below the spinal cord lesion is hypothesized to trigger a sympathetic surge leading to vasoconstriction and elevation in blood pressure and heart rate. The intact carotid and aortic baroreceptors detect this increase and relay with brainstem and hypothalamic centers. Normally, these centers would signal an inhibition to the preganglionic sympathetic neurons in the thoracic cord, but this feedback is disrupted. The parasympathetic counterbalance is also directly activated, leading to vasodilatation and bradycardia. Because it does not reach below the T6 level, however, the parasympathetic signal does not affect the large splanchnic vascular bed, and hypertension persists. For more information, refer to the articles ‘‘Management of Acute Spinal Cord Injury’’ by Deborah M. Stein, MD, MPH, FACS, FCCM, and Kevin N. Sheth, MD, FAHA, FCCM, FNCS, as well as the article ‘‘Management of Chronic Spinal Cord Dysfunction’’ by Gary M. Abrams, MD, FAAN, and Karunesh Ganguly, MD, PhD, . in this issue of CROSS-SECTIONAL SPINAL CORD LOCALIZATION Classic spinal cord syndromes are described based on the cross-sectional anatomical organization of the spinal cord, vascular supply, and surrounding structures of the spinal cord (Table 1-3).4Y6 These syndromes are useful clinical models to organize neurologic localization Continuum (Minneap Minn) 2015;21(1):13–35

as an aid to diagnosis of specific diseases, butVas with any syndromeVthe classifications are not completely specific and must be taken in the context of other symptoms and signs, neuroimaging, and ancillary data. Complete Cord Transection In complete transection, all descending and ascending pathways are severed (Figure 1-4). Typically, a spinal sensory level to all modalities will be found one to two segments below the actual level of injury. A flaccid paralysis (spinal shock) and associated ‘‘flaccid’’ autonomic dysfunction may occur acutely below the level of injury. Over time, spasticity and hyperreflexia ensue below the level of the lesion, with a segmental anterior horn syndrome sometimes present at the level of the lesion. Some transverse lesions are incomplete, depending on the severity of the injury. When due to inflammation, this syndrome is termed transverse myelitis. Longitudinally extensive lesions can cause chronic flaccid weakness if the anterior horns are involved throughout the length of the spinal cord. Neuromyelitis optica (NMO) causes a fulminant transverse and often longitudinally extensive myelitis that may affect all columns of the spinal cord. Paraneoplastic necrotizing myelopathy is a relentless progressive myelopathy that extends longitudinally over days to weeks. Late radiation-induced myelopathy (radiation myelitis) causes a slowly progressive spinal cord syndrome 6 to 24 months after exposure, which may begin as partial, but can involve the entire cross-sectional cord. For more information on radiation and paraneoplastic myelopathies, refer to the article ‘‘Neoplastic Myelopathies’’ by Marc C. Chamberlain, MD, FAAN, in this . Additionally, issue of for more information on inflammatory myelopathies, including NMO, refer to the

KEY POINTS

h Lesions (usually severe and acute) above T6 may lead to a phenomenon of autonomic dysreflexia.

h Longitudinally extensive lesions can cause chronic flaccid weakness if the anterior horns are involved throughout the length of the cord.



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Cross-sectional Spinal Cord Localization

TABLE 1-3 Syndrome

Clinical Features

Selected Causes

Complete cord transection

Bilateral upper motor neuron (UMN) pattern weakness below level

Trauma, transverse myelitis, hemorrhage, epidural abscess or metastasis, paraneoplastic necrotizing myelopathy, late radiation-induced myelopathy

Bilateral sensation loss below level Autonomic function loss below level Hemicord (Brown-Se´quard syndrome)

Ipsilateral UMN pattern weakness below level Ipsilateral lower motor neuron (LMN) pattern weakness at level

Penetrating trauma, multiple sclerosis, varicella-zoster virus, asymmetric compression

Ipsilateral vibration and position sensation loss below level Contralateral pain and temperature sensation loss below level Central cord syndrome

Small lesion: suspended pain and temperature sensation sensory level Large lesion: segmental LMN pattern weakness at level

Hyperextension injury, syringomyelia, intramedullary tumor, neuromyelitis optica

Bilateral UMN pattern weakness below level (arms worse than legs) Bilateral pain and temperature sensation loss below level (sacral sparing) Posterior column syndrome Bilateral vibration and position sensation loss below level Absent reflexes (knees, ankles) Sensory ataxia

Tabes dorsalis, cervical spondylotic myelopathy, posterior spinal artery infarction, early delayed radiation-induced myelopathy

Lhermitte sign (cervical) Posterolateral column syndrome

Bilateral vibration and position sensation loss below level Bilateral UMN pattern weakness below level Sensory ataxia, spastic gait

Vitamin B12 deficiency, copper deficiency, cervical spondylotic myelopathy, HTLV-I-associated myelopathy/tropical spastic paraparesis, hereditary spastic paraplegia, HIV, paraneoplastic myelitis

Anterior horn syndrome

Diffuse LMN pattern weakness

Poliovirus, West Nile virus, spinal muscular atrophy, spinobulbar muscular atrophy, paraneoplastic subacute motor neuronopathy

Combined anterior horn and corticospinal tract disease

Diffuse combined UMN pattern weakness and LMN pattern weakness

ALS, cervical radiculomyelopathy

Bulbar weakness Pure motor syndrome

Continued on next page

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TABLE 1-3

Cross-sectional Spinal Cord Localization (Continued)

Syndrome

Clinical Features

Selected Causes

Anterior cord syndrome

Bilateral LMN pattern weakness at levels affected

Anterior spinal artery infarction, poliovirus, West Nile virus

Bilateral UMN pattern weakness below Bilateral pain and temperature sensation loss below level Autonomic function loss below level Bilateral vibration and position sensation spared Sensory neuronopathy

Isolated bilateral nonYlength-dependent sensory loss Sensory ataxia

Conus medullaris syndrome

Flaccid bladder dysfunction early in course Bilateral ‘‘saddle’’ sensory loss

Paraneoplastic, SjPgren syndrome, celiac disease, chemotherapy, pyridoxine toxicity Lumbar disk disease, trauma, epidural metastasis or abscess (L1 or L2), cytomegalovirus, schistosomiasis

Mild bilateral lumbosacral LMN pattern weakness HTLV-I = human T-cell lymphotropic virus type I; HIV = human immunodeficiency virus; ALS = amyotrophic lateral sclerosis.

article ‘‘Immune-Mediated Myelopathies’’ by Benjamin M. Greenberg, MD, MHS, and Elliot M. Frohman, MD, PhD, FAAN, . in this issue of Hemicord (Brown-Se´quard) Syndrome Hemicord injury disrupts descending corticospinal fibers that have already crossed in the pyramidal decussations, leading to ipsilateral upper motor neuron weakness below the level of the lesion (Figure 1-5). If affecting the anterior horn, ipsilateral lower motor neuron weakness occurs in a segmental fashion at the level of the lesion, which may cause hemidiaphragm paralysis if it occurs at the level of C4 or above. This lower motor neuron weakness may be hard to identify clinically in thoracic lesions. Hemicord lesions lead to ipsilateral impairment of vibration and position sense below the level of the lesion (uncrossed ascending posterior columns) but affects contralateral pain and temContinuum (Minneap Minn) 2015;21(1):13–35

perature sensation (anterolateral spinothalamic tract) from one to two segments below the lesion, as these pathways cross within one to two segments from entering the spinal cord. Radicular pain (root irritation) or complete hemianesthesia (dorsal root compromise) at the level of the lesion may sometimes help localize the level. Damage to descending autonomic fibers may lead to ipsilateral loss of sweat below the lesion and ipsilateral Horner syndrome if the lesion is in the cervical region. Bladder dysfunction does not occur because this requires bilateral disruption of descending autonomic pathways. Penetrating trauma (eg, knife or gunshot) is a classic cause of hemicord syndrome, but can occur as a result of any cause of asymmetric spinal cord dysfunction.

KEY POINT

h Hemicord lesions lead to ipsilateral impairment of vibration and position sense below the level of the lesion (uncrossed ascending posterior columns) but affects contralateral pain and temperature sensation (anterolateral spinothalamic tract) from one to two segments below the lesion, as these pathways cross within one to two segments from entering the spinal cord.

Central Cord Syndrome A small central cord lesion disrupts bilateral-crossing spinothalamic fibers www.ContinuumJournal.com


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FIGURE 1-5

Hemicord (Brown-Se´quard) syndrome. S = sacral; L = lumbar; T = thoracic; C = cervical.

passing in the anterior commissure, causing loss of pain and temperature in one or more adjacent dermatomes bilaterally at the level of the lesion (Figure 1-6). Because the anterolateral tracts themselves are spared, sensation above and below the lesion remains

FIGURE 1-6

intact, leading to a ‘‘suspended’’ sensory level. As these lesions commonly affect the lower cervical and upper thoracic cord, the sensory loss is classically seen in a ‘‘cape’’ or ‘‘vest’’ distribution across the neck and shoulders or trunk, respectively. As a central lesion enlarges, it encroaches

Central cord syndrome. S = sacral; L = lumbar; T = thoracic; C = cervical.

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on anterior horn cells, causing segmental lower motor neuron weakness at the level of the lesion. Further expansion affects the lateral corticospinal tracts and anterolateral tracts, causing upper motor neuron weakness and temperature and sensation loss below the lesion. Due to the more lateral location of sacral fibers in the anterolateral tract, sacral sensation may be spared (sacral sparing). In an acute central cord lesion (typically from severe cervical hyperextension injury), initial quadriplegia evolves into a more prominent upper extremity upper motor neuron pattern weakness with relative sparing of the lower extremities, referred to as man-in-the-barrel syndrome. This syndrome may be due to the somatotopic pattern of the lateral corticospinal tracts, in which the cervical fibers are more centrally arranged and lumbosacral fibers are more laterally arranged. In addition to hyperextension injury, other common causes of central cord syndrome include syringomyelia and intramedullary tumor. NMO may affect the central cord initially but typically expands to a complete transverse cord syndrome.

FIGURE 1-7

Posterior Column Syndrome Damage to the posterior columns in isolation causes impairment in vibration and proprioception and a pronounced sensory ataxia with a ‘‘stomping’’ gait (Figure 1-7). If the dorsal roots are involved (as in tabes dorsalis), reflexes are absent, especially in knees and ankles, but strength is usually preserved. Cervical involvement may be accompanied by Lhermitte sign, presumably due to aberrant mechanical activation of damaged posterior columns with neck flexion. Injury to the spinocerebellar tracts in isolation may cause a truncal ataxia with preserved conscious proprioceptive sensation, which may be the only sign early in the course of extrinsic epidural compression, possibly reflecting a unique vulnerability of spinocerebellar tracts to compressive ischemia. In patients with chronic posterior column dysfunction, the loss of joint sensation may lead to repeated microtrauma, and dysregulated autonomic control of blood flow to the joints increases osteoclastic resorption, both causing neuropathic joints (Charcot arthropathy).

KEY POINTS

h In an acute central cord lesion (typically from severe cervical hyperextension injury), initial quadriplegia evolves into a more prominent upper extremity upper motor neuron pattern weakness with relative sparing of the lower extremities, referred to as man-inthe-barrel syndrome.

h Damage to the posterior columns in isolation causes impairment in vibration and proprioception and a pronounced sensory ataxia with a ‘‘stomping’’ gait.

Posterior column syndrome. S = sacral; L = lumbar; T = thoracic; C = cervical.

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h In some posterolateral column processes, the clinical involvement of the posterior columns is less manifest, leading to an upper motor neuron pattern with bladder dysfunction but only mild or subclinical sensory impairment.

Tabes dorsalis due to neurosyphilis is the canonical disease associated with posterior column syndrome, but early cervical spondylotic myelopathy is the most common cause. Early delayed radiation-induced myelopathy presumably causes temporary demyelination in the posterior columns, manifested mainly by Lhermitte sign. Although the posterior columns constitute a vascular territory, the robust plexus and paired posterior spinal arteries make infarcts in this distribution extremely rare. Posterolateral Column Syndrome Involvement of the posterior columns and lateral corticospinal tracts leads to impairments in vibratory and proprioceptive sensation and upper motor neuron weakness, with relative sparing of pain and temperature sensation (Figure 1-8). Patients develop a spastic and ataxic gait, and reflexes may be increased due to corticospinal tract disruption, but may also be depressed (especially ankle jerks) due to con-

FIGURE 1-8

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comitant involvement of large myelinated peripheral nerves. Descending autonomic pathways may also be involved, leading to a spastic bladder. Vitamin B12 deficiency classically causes this pattern of subacute combined degeneration, and copper deficiency can cause a similar syndrome. For more information on myelopathy related to vitamin B12 and copper deficiency, refer to ‘‘Metabolic and Toxic Causes of Myelopathy’’ by Brent P. Goodman, MD, in . this issue of Posterior extrinsic compression, as in cervical spondylosis, may cause a similar posterolateral column syndrome. Paraneoplastic myelitis may cause lateral, posterior, or combined posterolateral column syndrome. In some posterolateral column processes, the clinical involvement of the posterior columns is less manifest, leading to an upper motor neuron pattern with bladder dysfunction, but with only mild or subclinical sensory impairment (eg, Human T-cell lymphotropic virus type IYassociated myelopathy/tropical spastic paraparesis and hereditary spastic paraplegia).

Posterolateral cord syndrome.



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Anterior Horn Syndrome Selective damage to anterior horn cells causes a flaccid weakness with atrophy and fasciculations with reduced or absent reflexes (Figure 1-9). Cranial motor nuclei may also be involved, and no sensory involvement occurs. Poliovirus is the textbook example of a disease causing this syndrome. Other nonpolio enteroviruses and flaviviruses such as West Nile virus and Japanese encephalitis virus may also primarily affect the anterior horn. For more information on infectious myelopathies, refer to the article ‘‘Myelopathy Associated with Microorganisms’’ by Jennifer L. Lyons, . MD, in this issue of In children, spinal muscular atrophy is the most important cause of anterior horn syndrome. Spinobulbar muscular atrophy (Kennedy disease) causes a slowly progressive anterior horn syndrome in men ages 20 to 60. Lower motor neuron disease associated with paraneoplastic subacute motor neuronopathy is infrequently reported.

FIGURE 1-9

Combined Anterior Horn and Corticospinal Tract Disease The combination of upper and lower motor neuron signs with sparing of sensory function is a distinctive pattern most suggestive of ALS (Figure 1-10). Cramping is a commonly associated symptom, but bladder function is typically preserved due to sparing of the sacral motor neurons in the Onuf nucleus. Cervical radiculomyelopathy can cause a segmental lower motor neuron pattern of weakness with upper motor neuron findings below the lesion.

KEY POINT

h In anterior (spinal artery) cord syndrome, patients have an upper motor neuron pattern of weakness, loss of pain and temperature below the level of the lesion, and bladder incontinence but preserved vibration and position sense.

Anterior Cord Syndrome Due to the vascular territory of the anterior spinal artery, this syndrome involves lateral corticospinal tracts, anterior horns, spinothalamic tracts, and descending autonomic fibers, but spares posterior columns (Figure 1-11). Patients have an upper motor neuron pattern of weakness, loss of pain and temperature below the level of the lesion, bladder incontinence,

Anterior horn syndrome. S = sacral; L = lumbar; T = thoracic; C = cervical.




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FIGURE 1-10

Combined anterior horn and corticospinal tract disease. S = sacral; L = lumbar; T = thoracic; C = cervical.

but preserved vibration and position sense, which is sometimes referred to as anterior spinal artery syndrome as it was originally defined by ischemic damage to the vascular territory. For more information, refer to the article ‘‘Vascular Myelopathies’’ by Alejandro

FIGURE 1-11

A. Rabinstein, MD, FAAN, in this issue . Some processes of that cause anterior horn syndrome (eg, West Nile virus) can extend into the lateral columns but spare the posterior columns, leading to an anterior cord syndrome.

Anterior cord (anterior spinal artery) syndrome. S = sacral; L = lumbar; T = thoracic; C = cervical.

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February 2015

Sensory Neuronopathy The dorsal root ganglia neurons are rarely selectively injured, leading to a nonYlength-dependent pure sensory syndrome, involving both posterior columns and peripheral sensory nerve fibers. Patients have dysesthesia, areflexia, and severe sensory ataxia, which may occur as part of a paraneoplastic syndrome or in the setting of systemic connective tissue disease, especially Sjo ¨gren syndrome. Although not strictly a spinal cord syndrome, sensory neuronopathy may involve the posterior columns and often progresses to myelitis in paraneoplastic disease. Platinum-based chemotherapy and pyridoxine toxicity are other causes of sensory neuronopathy. LONGITUDINAL SPINAL CORD LOCALIZATION In addition to cross-sectional cord syndromes, certain clinical features can be the clues to the longitudinal spinal level of injury (Table 1-4).4,7 A spinal sensory level is the most useful sign to determine longitudinal localization. Typically, the lesion is two segments rostral to the sensory level. Additionally, other segmental signs can be useful to help refine longitudinal localization. Cervicomedullary Junction and Upper Cervical Spinal Cord Lesions at the cervicomedullary junction that affect the pyramidal decussations may cause an ‘‘around the clock’’ pattern of weakness. Because the upper extremity pyramidal fibers cross more rostral to the lower extremity pyramidal fibers and the fibers for one side frequently cross completely before the other, an upper motor neuron pattern of weakness spreads from ipsilateral upper extremity, to ipsilateral lower extremity, to contralateral lower extremity, to contralateral upper extremity. With extrinsic lesions, pain in the occiput and neck are common. Obstruction of CSF Continuum (Minneap Minn) 2015;21(1):13–35

outflow at the foramen may lead to downbeat nystagmus and papilledema. Extension into the caudal brainstem may cause lower cranial nerve palsies. High cervical cord lesions may cause diaphragmatic weakness and respiratory failure as the phrenic nerve arises from rootlets at C4-C5. The spinal trigeminal nucleus descends as low as C4, so cervical lesions above that level may cause facial numbness in a circumferential ‘‘onion skin’’ pattern. It is important to note that high cervical lesions can sometimes manifest with lower cervical and upper thoracic lower motor neuron signs, presumably due to venous congestion or anterior spinal artery compression affecting the more caudal anterior horns. Extramedullary causes of foramen magnum and high cervical lesions include meningioma, neurofibroma, glioma, spondylosis, Chiari malformation, and trauma; intramedullary etiologies include syringomyelia, multiple sclerosis (MS), and NMO.

KEY POINTS

h A spinal sensory level is the most useful sign to determine longitudinal localization.

h Lesions between C5 and T1 are most readily localized when they cause radicular pain and numbness and segmental lower motor neuron weakness with a caudal upper motor neuron pattern.

Lower Cervical and Upper Thoracic Spinal Cord Lesions between C5 and T1 are most readily localized when they cause radicular pain, numbness, and segmental lower motor neuron weakness with a caudal upper motor neuron pattern. At C5-C6, lesions lead to depression of biceps and brachioradialis reflexes with exaggerated triceps and finger flexor reflexes. Tapping the brachioradialis causes no flexion or supination of the forearm, but elicits a brisk finger flexor response. With lesions at C7, biceps and brachioradialis reflexes are preserved, triceps reflex is depressed, and finger flexor reflex is exaggerated. At C8-T1, the finger flexor reflex is depressed. Involvement of the sympathetic outflow from the intermediolateral cell column at C8-T1 may cause Horner syndrome and provide a clue to this localization. www.ContinuumJournal.com


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TABLE 1-4

Longitudinal Spinal Cord Localization

Cord Location/Syndrome

Clinical Features

Notes

Foramen magnum/upper cervical

Occipital, neck pain

False localizing signs include C6 to T3 sensory and lower motor neuron (LMN) signs

‘‘Around the clock’’ upper motor neuron (UMN) weakness Lower cranial nerve signs Downbeat nystagmus Diaphragmatic paralysis Trigeminal ‘‘onion skin’’ numbness

Lower cervical/upper thoracic

Radicular pain and numbness

Causes include meningioma, neurofibroma, glioma, syringomyelia, trauma, spondylosis, Chiari malformation, multiple sclerosis, and neuromyelitis optica Extramedullary compressive lesions most common

Segmental LMN weakness, UMN weakness caudal Segmental areflexia with hyperactive reflexes caudal Thoracic

Dermatomal pain and sensory level T6 to T12 superficial spinal reflexes T10 Beevor sign

Lumbosacral

Radicular pain and numbness Segmental LMN weakness, UMN weakness caudal

Autonomic dysreflexia if lesion above T6; lesions tend to be more complete due to small diameter and relative vascular border zone Extramedullary compressive lesions most common

Segmental areflexia with hyperactive reflexes caudal Conus medullaris

Flaccid bladder dysfunction early in course Bilateral ‘‘saddle’’ sensory loss Mild bilateral lumbosacral LMN weakness

Cauda equina

Radicular pain Asymmetric lumbosacral sensory loss Marked asymmetric lumbosacral LMN weakness

Lumbar disk disease, trauma, epidural metastasis or abscess (L1 or L2), cytomegalovirus, schistosomiasis

Lumbar disk disease, trauma, epidural metastasis or abscess (L3 or lower), cytomegalovirus, schistosomiasis

Flaccid bladder dysfunction late in course Absent reflexes (knees, ankles)

Thoracic Spinal Cord A sensory level and dermatomal pain (eg, intercostal neuralgia) are the most obvious indicators of thoracic cord lesions. Because of the minimal motor

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control by thoracic motor neurons, segmental lower motor neuron involvement is not readily apparent. Because of the small diameter and the relative vascularYborder-zone territory of the



February 2015

thoracic cord, lesions tend to progress to complete cord syndrome more rapidly than in the cervical and lumbar regions. Lesions above T6 may lead to autonomic dysreflexia due to disruption of sympathetic outputs from the splanchnic vascular bed. T6 lesions will also abolish superficial spinal (abdominal) reflexes. Lesions at T10 will spare the upper and middle abdominal reflexes, but the lower abdominal reflex will be absent, and lesions below T12 will not affect superficial abdominal reflexes. Another unique indicator of a T10 lesion is a Beevor sign. With neck flexion against resistance (eg, abdominal crunch), preserved upper abdominal muscles will pull the umbilicus upward against the weakened lower abdominal muscles. Lumbosacral Spinal Cord As with lower cervical and upper thoracic cord lesions, the segmental lower motor neuron weakness pattern and reflexes can help refine localization to specific levels. A lesion at L1 will cause spastic paraparesis with increased patellar and ankle reflexes. Lesions from L2 to L4 will cause varying patterns of weakness and numbness corresponding to segmental levels, with loss of patellar reflexes and increase in ankle jerks, while an L5 lesion will spare patellar reflexes and cause hyperactive ankle reflexes. Finally, S1-S2 lesions will abolish the ankle reflexes without impacting the patellar. Conus Medullaris and Cauda Equina Syndromes Lesions affecting the conus medullaris (sacral spinal cord, typically vertebral level L2 [Figure 1-1]) cause early flaccid bladder and bowel dysfunction, late and mild pain, and symmetric sensory impairment in a saddle distribution. Sensory loss may be dissociated. Ankle jerks (S1) are absent, but knee jerks Continuum (Minneap Minn) 2015;21(1):13–35

(L2 to L4) are typically preserved. Motor impairment is relatively mild and symmetric. Conus medullaris syndrome can be impossible to differentiate from cauda equina syndrome on clinical grounds. Due to lesions affecting the lumbosacral nerve roots, cauda equina syndrome is typically heralded by radicular pain in one or both lower extremities, asymmetric sensory loss to all modalities in the lumbosacral dermatomes, and onset of bladder and bowel dysfunction occurring later in the course compared with conus medullaris syndrome. Weakness is generally more marked and asymmetric compared with conus medullaris syndrome, and ankle and knee jerks are absent. External compression due to disk herniation, epidural metastasis, or epidural abscess may cause either syndrome, depending on location. Certain infections, particularly cytomegalovirus and schistosomiasis, have a tropism for the conus and lumbosacral nerve roots. For more information on cauda equina syndrome, refer to article ‘‘Disorders of the Cauda Equina’’ by Andrew W. Tarullli, MD, in . this issue of

KEY POINTS

h Due to lesions affecting the lumbosacral nerve roots, cauda equina syndrome is typically heralded by radicular pain in one or both lower extremities, asymmetric sensory loss to all modalities in the lumbosacral dermatomes, and onset of bladder and bowel dysfunction occurring later in the course compared with conus medullaris syndrome.

h When considering the diagnosis of a spinal cord lesion, the first step is to determine if the lesion is compressive as this constitutes a surgical emergency when symptoms present acutely.

CLINICAL APPROACH When considering the diagnosis of a spinal cord lesion, the first step is to determine if the lesion is compressive as this constitutes a surgical emergency when symptoms present acutely. While not completely specific, several features can help differentiate compressive extramedullary processes from intramedullary lesions. Extramedullary lesions cause radicular pain, which is exacerbated by movement, a Valsalva maneuver, straight leg raise, neck flexion, and notably recumbent positioning. Vertebral pain is localized to the level of the lesion and may be worsened with palpation or percussion. Central pain is more characteristic of intramedullary lesions affecting the spinothalamic www.ContinuumJournal.com


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h In a spinal cord lesion, reflexes typically will be preserved or increased, but reflexes may be depressed or absent (spinal shock) early in the injury.

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tracts or posterior columns and is usually described as vague and deep, often in places distant from the actual lesion. Because the corticospinal tracts are situated laterally, upper motor neuron signs occur early in extramedullary compressive lesions, whereas lower motor neuron involvement is more suggestive of intramedullary processes (Figure 1-4). The exception is segmental lower motor involvement that sometimes occurs at the level of a compressive lesion. In general, extramedullary lesions will affect ipsilateral upper and lower extremity motor function before progressing to contralateral weakness, whereas intramedullary lesions are more likely to simultaneously cause bilateral (especially upper extremity) motor dysfunction. In addition to radicular sensory changes, ascending sensory loss typifies extramedullary lesions as the superficially situated caudal dermatomes are most susceptible to compression early. Conversely, intramedullary lesions cause descending sensory loss with sacral sparing as those fibers are most lateral. Bladder and bowel disturbances due to lesions above S2 to S4 usually occur only with bilateral lesions. In conus medullaris syndrome, (intramedullary) sphincter dysfunction is an early feature compared with external compression of cauda equina. While these general patterns can aid in clinical localization, the clinician cannot rely fully on symptoms and signs to exclude a compressive lesion and should obtain neuroimaging to exclude this neurologic emergency. While the longitudinal and crosssectional features discussed previously in the article are useful tools, false localizing signs and other misleading presentations should always be considered. As noted, external cord compression may cause ascending sensory loss, and this pattern may be mistaken for

Guillain-Barre´ syndrome. In a cord lesion, reflexes typically will be preserved or increased, but reflexes may be depressed or absent (spinal shock) early in the injury. Similarly, when the anterior horns are involved, a flaccid weakness will predominate, which may falsely suggest a peripheral process. Exacerbation of symptoms with exertion may occur with lumbar spinal stenosis (neurogenic claudication) or with peripheral vascular disease (vascular claudication). Less commonly, spinal dural arteriovenous fistulas may be associated with exertional worsening due to increased venous congestion. The Uhthoff sign of worsening demyelinating disease symptoms due to heat may be interpreted as exertional worsening. Lesions at the cervicomedullary junction can manifest with an unusual pattern of weakness owing to the sequential decussation of upper and lower extremity pyramidal fibers from one side before the other. High- to midcervical lesions can sometimes cause a lower motor neuron pattern several levels caudal to the lesion, presumably due to venous congestion below the lesion. A numb clumsy hand syndrome can occur with compressive lesions that compromise the central border zone between superficial and deep arterial supply in the lower cervical cord. Patients have a glove distribution of sensory loss with only mild motor findings. Knowledge of the syndromes described in this article can refine cord localization and point toward specific etiologies. NeuroimagingValmost always MRIVshould be used to confirm localization and better delineate the degree of involvement. Other studies such as brain MRI, CSF examination, and neurophysiology studies are often necessary to further characterize the nature and extent of the process. Targeted testing for specific diseases



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can then be rationally pursued based on the pattern and context. CONCLUSION Knowledge of the neuroanatomic organization of the spinal cord aids the clinician in recognizing syndromes associated with injury to specific regions of the spinal cord. MRI is usually necessary to exclude compressive lesions and to confirm and refine the location and nature of injury. The spinal cord syndrome and MRI findings can direct investigations for specific etiologies. REFERENCES 1. Moore KL, Dalley AF, Agur AMR. Clinically oriented anatomy. 7th ed. Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins Health, 2014:xxviii:1134.


2. Fitzgerald MJT, Gruener G, Mtui E. Clinical neuroanatomy and neuroscience. 6th ed. London, UK: Saunders Elsevier, 2012. 3. Waxman SG. Clinical neuroanatomy. 26th ed. New York, NY: McGraw-Hill Medical, 2010:xi:371. 4. Brazis PW, Masdeu JC, Biller J. Localization in clinical neurology. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2011. 5. Bican O, Minagar A, Pruitt AA. The spinal cord: a review of functional neuroanatomy. Neurol Clin 2013;31(1): 1Y18. doi:10.1016/j.ncl.2012.09.009. 6. Campbell WW. DeJong’s the neurologic examination. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2005. 7. Dobkin BH, Havton LA. Paraplegia and spinal cord syndromes. In: Daroff RB, Fenichel GM, Jankovic J, Mazziotta JC, editors. Bradley’s neurology in clinical practice. 6th ed. Philadelphia, PA: Saunders Elsevier, 2012.



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