THE RADIOLOGICAL EVALUATIOI OF THE CHILD WITH A MYELOMENINGOCELE Sharon E. Byrd, MD, and Mary Ann Radkowski, MD Chicago, Illinois
Seven hundred fifty-five children with myelomeningoceles were evaluated radiologically at the Children's Memorial Hospital in Chicago. From our material, we propose a diagnostic radiologic model to accurately evaluate the neurological problems in the myelomeningocele child. This model is based on the clinical symptoms in these children and the radiologic modalities of magnetic resonance imaging (MRI), computed tomography (CT), ultrasound, myelography, and plain radiographs. We found MRI to be the best modality to evaluate the posterior fossa and total spine. Computed tomography and ultrasound are used to evaluate ventricular size. At times MRI may not adequately diagnose subtle cases of tethering of the spinal cord, cord infarction, arachnoid cysts, or diastematomyelia. In these cases, further evaluation may be necessary with real time ultrasound to look at cord pulsations and water soluble myelography with follow through CT to differentiate cord infarction, arachnoid cyst, localized hydromyelia, or diastematomyeFrom the Division of Neuroimaging, Department of Radiology, Children's Memorial Hospital, Northwestern University Medical School, Chicago, Illinois. Requests for reprints should be addressed to Dr Sharon E. Byrd, Division of Neuroimaging, Department of Radiology, Children's Memorial Hospital, Northwestern University Medical School, 2300 Children's Plaza, Chicago, IL 60614. 608
lia. If MRI is not adequate to completely visualize the cord because of the severe nature of the scoliosis, then water soluble myelography with CT is indicated. (J Nati Med Assoc. 1991 ;83:608-61 4.) Key words * myelomeningocele * diagnosis * magnetic resonance * computed tomography ultrasound -
Between 6000 and 11 000 babies are born with a myelomeningocele each year in the United States. Over the last quarter of a century, a great deal of attention has been directed in the medical literature as to how to treat, manage, and evaluate these patients. At the Children's Memorial Hospital in Chicago, we have treated and managed more than 1000 patients with myelomeningoceles through an interdisciplinary health professional team. In our experience, an aggressive medical approach has resulted in a lower mortality rate and a better quality of survival for the majority of our myelomeningocele children. With an increasing awareness and acceptance of disabled children and adults in our society, we feel that it is imperative that these children with a myelomeningocele be managed aggressively.1 2 Because the underlying abnormality is the congenital malformation that affects the total neural axis, a myriad of neurological problems confront these children. We propose a diagnostic radiologic model to accurately evaluate the neurological problems in the child with a myelomeningocele based on the clinical symptoms and JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
EVALUATION OF MYELOMENINGOCELE
Radiologic Protocol Newborn With Unoperated Myelomeningocele (M/IM)
Symmetric neurologic deficits rule out hydrocephalus
I
US or CT (head)
Nl I,
Surgical repair of M/M with or without VP shunt
Severe asymmetric neurologic deficits rule out hemimyelocele
If
MR (head and spine or CT myelography)
Surgical repair
of M/M
Figure 1. Radiologic protocol for the newborn with unoperated myelomeningocele.
radiologic modalities of magnetic resonance imaging (MRI), computed tomography (CT), ultrasound, myelography, and plain radiographs. This radiologic model is designed to simplify and to determine which are the best radiologic tests to use in the neurologic evaluation of children with a myelomeningocele (Figures 1 and 2).
MATERIALS AND METHODS Over the past 3 years at the Children's Memorial Hospital in Chicago, we radiologically evaluated 300 children born with a thoracolumbar, lumbar, or lumbosacral myelomeningocele. Seventy-two of these children were evaluated before, and 300 children were evaluated after the myelomeningocele was repaired. They ranged in age from newborn to 17 years, and the sex predilection was 170 girls to 130 boys. The common symptoms were a back mass at birth (myelocele or myelomeningocele), hydrocephalus, headaches, lethargy, vomiting, apnea, stridor, paraparesis or paraplegia, deteriorating neurologic function, bladder and bowel incontinence, and scoliosis. The radiologic modalities used to evaluate the children consisted of CT, MRI, ultrasound, CT myelography, and plain radiographs of the spine. The CT scans were of the head, noncontrast studies, axial projection, 3-mm to 5-mm slice thickness, and contiguous table movement. The MRI scans were of the head (with an emphasis on the posterior fossa) and total spine in the sagittal projection performed with TI weighted JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
Radiologic Protocol
Repaired M/M Child A? Later deterioration Signs of t ICP of neurological hydrocephalus or functon Shunt mafunction I H (1) MR Head US wih indices or CT or MR MR (a) Braln to evaute for: 1. Dyspistc or hypoplastic stnhxres 2. C cdullary kInk for obsion, synngobulbia, amchnoid cyst 3. Hydrocephalus (b) Total spine to evaluate for: 1. Hydromyelia, a i cyst, atrophy 2. D ltmtolia 3. Tethering 4. Inclusion (epQdefnoids, lipomas. (2) AdJunct procedures to MR US of (a) spine to evaluate for: pulsations in subtle cases of tetheing (3) CT myelography
'I
(b) Arachnoid cyst, atrophic cord,
hydromyelia, diastematomyelia scoliosis, kyphoscoliosos (4) Plain lumbosacral radiographs
severe
(a) To evaluate severiy of scoliosis Figure 2. Radiologic protocol for the repaired myelomeningocele child.
spin echo (SE) pulse sequences with a repetition time (TR) of 500 to 600 milliseconds, and an echo time (TE) of 20 to 30 milliseconds. Axial TI weighted MRI scans through the lumbosacral area also were obtained routinely. The slice thickness was 3 mm to 5 mm without a gap or with a 0.5-mm gap. At times, additional pulse sequences proton density (SE, TR 2000/TE 30), T2 weighted (SE, TR 2000/TE 90), or gradient echo acquisitions T2* (TR 200-400/TE 20-30 and flip angle 100 to 150) were obtained as well as other projections axial or coronal through localized areas of the posterior fossa or spine. The matrix size was 256 x 609
EVALUATION OF MYELOMENINGOCELE
Figure 3. Ultrasound Doppler indices of the head (a,b) demonstrating measurement of the pulsatile index and resistive index of the anterior cerebral artery. Coronal ultrasound (c,d) of the head demonstrating hydrocephalus with dilated frontal and temporal horns (small arrows) and bodies (large arrows) of the lateral ventricles. 128 or 256 and the number of excitations were 1, 2, or 4. The ultrasound was of the head or lumbosacral spine using a real-time unit with 5 MHz or 3 MHz sector and linear-array transducers. The myelograms were performed with Tohexol (Omnipaque, Barceloneta, Puerto Rico) 180 or 240 with 2 mL to 10 mL injected into the thecal sac via a lumbar puncture lateral to the repair site with conventional filming and then always followed by an axial CT survey of the total spine immediately after the myelogram and with a delayed axial CT survey (4 to 6 hours later). Plain radiographs of the spine were performed conventionally with only anteroposterior (AP) and lateral projections. The equipment used was a GE 9800 (Milwaukee, Wisconsin) or Interad CT (Chicago, Illinois) scanner, 0.5T Elscint (Tel Aviv, Israel) or 1 .5T GE MRI (Milwaukee, Wisconsin) scanner, Accuson (Mountain View, California) real-time ultrasound scanners both with and without color doppler and conventional equipment for the myelograms and plain radiographs. The children were sedated when necessary for the CT or MRI studies with chloral hydrate 50 to 100 mg/kg orally with a maximumn of 2 g. Nembutal 2 mg/kg (TM), nubaine 0. 15 mg/kg (TM), and chloral hydrate 50 mg/kg were for the mylga T T
used
610
Figure 4. A newborn with a myelomeningocele
(arrow). signs were monitored with a pulse oximeter for the CT and myelogram CT and manually by a nurse in the room with the magnet for the MRI.
RESULTS AND DISCUSSION Depending on the symptoms, a baby born with a myelomeningocele may or may not require detailed radiological evaluation. The majority of newborns with an unoperated myelomeningocele have slightly asymmetric or symmetric neurologic deficits. These patients require urgent surgical repair of the myelomeningocele to prevent exacerbation of their handicaps or death.3 The only radiological role in these patients is to image the head to evaluate for hydrocephalus, via either ultrasound or CT (Figure 3). Depending on the degree of ventricular dilatation, the neurosurgeon may elect to shunt the ventricles at the same sitting as the repair of the myelomeningocele (Figure 4). Newborns with unoperated myelomeningoceles who exhibit severe asymmetric neurologic deficits will require more extensive imaging modalities in order to rule out a hemimyelocele (diastematomyelia).3 The first modality is MRI of the head and spine to evaluate the degree of ventricular dilatation as well as to evaluate the JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
EVALUATION OF MYELOMENINGOCELE
Figure 6. MRI sagittal brain scan (SE 500/20). (a) The small arrow indicates Chiari 11 with a diverticulum of the fourth ventricle, and the large arrow indicates an arachnoid cyst of the posterior fossa. (b) Chiari 11 and IV are indicated; a severely dysplastic posterior fossa with a thinned downward displaced brainstem and a marked hypoplastic cerebellum with only a nubbin of cerebral tissue present (arrow) are compatible with a Chiari IV.
Figure 5. MRI sagittal brain scan (SE 500/20). The arrow indicates Chiari 11 malformation with cervicomedullary kink at C2 to C3 level.
posterior fossa and total spinal axis to rule out a localized area of diastematomyelia. The MRI should be performed with TI-weighted images in sagittal and axial planes. If subtle abnormalities are seen, then further, more invasive procedures may have to be performed such as myelography CT to rule out partial or complete clefting of the cord and to locate the diastematic spur. The greatest radiological role is in evaluating the child postoperatively.3'4 Children who have had successful surgical repair should remain stable, and a few will go on to improve with a gain in some neurological functions. The child with a repaired myelomeningocele who starts to deteriorate is the child who requires greater radiological evaluation. In these cases, the whole neural axis should be imaged. However, depending on the symptoms, greater emphasis should be directed toward certain areas of the neural axis. The most common complications that these patients develop is hydrocephalus and shunt malfunction. Ninety-eight percent of patients with myelomeningoceles develop ventricular dilatation. Between 80% and 90% of these patients require shunt diversion of the cerebrospinal fluid (CSF).4 These patients commonly present with full fontanelle, rapidly increasing head circumference, and poor feeding (signs of increased intracranial pressure). Depending on the age of the JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
child, ultrasound of the head in children less than 1 year of age or a noncontrast CT scan in children over 1 year old should be used to evaluate the degree of ventricular dilatation. In infants who have or have not been shunted, the ultrasound with indices has proven to be a reliable index of increased intracranial pressure. The indices of the anterior cerebral artery are obtained and an increase in the pulsatile index and resistive index are used in conjunction with the size of the ventricular system on ultrasound to determine whether these children should be followed or shunted (Figure 3).5 Patients with myelomeningoceles have a 99% association with Chiari II malformation. This is a congenital anomaly of the hindbrain in which there is herniation of the medulla and at times the pons, fourth ventricle, and inferior aspect of the cerebellum into the upper cervical canal usually between C2 to C4 but the herniated contents may extend down to T 1.6 Patients with significant compression of hindbrain structures (brainstem) at the craniocervical junction or within the cervical canal may present with apnea, stridor, vomiting, poor tolerance to changes in food texture with choking, or respiratory distress.2 These symptoms may be due to significant compression of the hindbrain structures or to dysplasia of posterior fossa contents, which can also occur in patients having Chiari II malformation. The MRI is the first modality of choice in evaluating the posterior fossa and upper cervical canal. The sagittal TI -weighted images of the posterior fossa and upper cervical canal demonstrate the location of the cervicomedullary kink in 70% of the cases (Figure 5). It can also demonstrate whether there is an associated 611
EVALUATION OF MYELOMENINGOCELE
Figure 8. (a) CT axial scan. Scan taken after water-soluble lohexol myelogram with con trast material within subarachnoid space of the thoracic spine (small arrows) and within a large posterior intrathecal arachnoid cyst (large arrows) with displacement of the spinal cord (open arrow) anteriorly. (b) MRI axial scan (SE 500/20) of thoracic spine of the same patient as in 6a showing an arachnoid cyst (large arrow) of the same intensity as adjacent CSF of the thecal sac with anterior displacement of the cord (small arrow).
Figure 7. MRI sagittal scans (SE 600/30). (a) andAsaita Thoracic spine with (b) lumbar MR "bamboo" othtta therepir ite4 Ti.''!-wihe appearance to the cord are indicative of hy-
iw,
dromyelia. arachnoid cyst, hydromyelia, or syringobulbia involving the upper cervical cord, medulla, or craniovertebral junction. T2-weighted or gradient echo (T2*) views will help to determine the presence of CSF spaces (cisterns) at the level of the cervicomedullary kink. Depending on the degree of obstruction as manifested by no demonstration of CSF spaces around the cervicomedullary kink, either posterior fossa decompression may be necessary or shunting of the area of localized hydromyelia or syringobulbia. Also, at times the respiratory distress is secondary to dysplasia of posterior fossa structures, especially the medulla. The MRI will help to determine if a surgical condition exists (Figure 6). Patients who have an increase in scoliosis or a deterioration of neurological function such as increasing motor and sensory deficits within the lower extremities or bowel and bladder problems may have hydromyelia, arachnoid cyst, cord infarction with atrophy, diastematomyelia, or retethering of the spinal cord by scarring, inclusion epidermoids, or lipomas at
612
Figure 9. (a) MRI axial scan (SE 500/20) of the lumbar spine showing diastematomyeliatwo spinal cords (arrows). (b) CT axial scan of upper thoracic spine with intrathecal lohexol demonstrating the two spinal cords (arrows)diastematomyelia.
spine is the first modality to evaluate these conditions. Between 20% and 60% of patients with myelomeningoceles may have hydromyelia. The area of hydromyelia may be focal, multiple, or diffuse extending throughout the total spinal cord. One of the first indications of a significant hydromyelia clinically is rapid progressive kyphoscoliosis. The hydromyelia may be secondary to hydrocephalus with resultant transmission of CSF through the obex down into the central canal and distention secondary to the increased hydrostatic pressure from above. Multiple diffuse areas of hydromyelia are usually easily identified on sagittal Tl MRI studies. If the "bamboo appearance" to the spinal cord is identified, this is classic for hydromyelia (Figure 7)s3d4 JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
EVALUATION OF MYELOMENINGOCELE
Figure 11. (a) Plain AP spine radiograph show ing levoscoliosis of thoracolumbosacral spine. (b) Coronal MRI scan (SE 600/30) illus trating suboptimal demonstration of the spin nal cord (arrows). (c) Water-soluble myelo gram demonstrating low-lying tethered cord (arrows) against right side of the spinal canal.
Figure 10. MRI sagittal thoracolumbosacral scan (SE 600/30) showing (a) spinal cord tethered at distal end by scar (arrow) at the repair site and (b) increased lordosis to the lumbosacral spine indicative of retethering. At surgery, the cord was tethered by scar along the posterior wall of the thecal sac in the lumbosacral area.
At times, it may be difficult to distinguish localized areas of hydromyelia from an arachnoid cyst or areas of localized cord atrophy secondary to cord infarction. An axial TI may help to differentiate cord atrophy from these other two conditions. Usually, more invasive studies are necessary to accurately differentiate these three conditions. A water-soluble myelogram with a follow-up CT will differentiate these conditions. In patients who have localized atrophy, the cord is small and within the center of the thecal sac. In children who have an arachnoid cyst, the cord would be displaced by a cystic mass that is easily identified on the CT myelogram. In patients who have hydromyelia, the delayed CT-myelogram study will demonstrate the water-soluble contrast material to be within the central portion of the spinal cord (Figure 8). Diastematomyelia occurs in 30% to 40% of patients with myelomeningoceles.3,4 The area of the diastematomyelia is at the site of the myelomeningocele in 20% of JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
the cases, cephalic to this site in 30%, and caudal to this site in 25%. In evaluating these children for diastematomyelia, the coronal MRI is the best projection. If a suspicious area is identified on the coronal projection, then axial views of this area should be obtained. However, the MRI is not as sensitive in detecting diastematomyelia, and if there is suspicion, then a water-soluble myelogram with follow-up CT should be obtained. This is the most sensitive test to adequately evaluate the spine for partial or complete clefting (Figure
9). One of the most common problems that occurs in the child with a myelomeningocele is retethering at the repaired site. This was extremely common when the older technique of repair was used without producing a sling to hold the cord away from the posterior wall of the repaired thecal sac.2'3 The sagittal TI MRI of the cord with additional axial Ti-weighted images through the repair site can adequately evaluate retethering in the majority of cases. The classical findings consist of a straightened, taut, bow-string cord with its distal end adherent to the posterior wall of the thecal sac along the repaired site. In addition, there may be irregularity of the distal cord blending into the repaired wall of the thecal sac. These are findings of tethering by scar formation. Another sign is increase in the lordosis of the lumbosacral canal at the level of the repair with adherence of the spinal cord to the posterior wall of the spinal canal at the apex of the lordosis (Figure 10). The cord also may be tethered by an inclusion epidermoid or lipoma at the repair site. The MRI will demonstrate a mass within the distal aspect of the thecal sac near the repair site. The cord will be taut, and its distal end will blend into the mass. If the mass is of a similar signal as adjacent cord, then it is an inclusion epidermoid. If it is bright on the TI-weighted images 613
EVALUATION OF MYELOMENINGOCELE
(the same signal as subcutaneous fat), then it is an inclusion lipoma. At times, it may be difficult to definitely diagnose retethering at which time real-time ultrasound to image cord pulsations is necessary. If there are absent pulsations of the cord at the repair site in the neutral position or if the back is flexed and the cord pulsations disappear, then these are signs of significant tethering of the cord.7 Scoliosis, kyphoscoliosis, gibbus deformity, and severe lordosis present significant problems in the repaired myelomeningocele child. The abnormal curvature of the spine may be due to untreated hydromyelia, tethering, neuromuscular imbalance, one or more hemivertebrae with congenital bars, or a special form of musculoskeletal imbalance secondary to coronal orientation of all of the paraspiral muscles and adjacent laminae at one or more levels of the spinal dysraphism.4 Depending on the severity of and location of the abnormal curvature, it may not be possible to adequately evaluate these children with only MRI. Plain radiographs of the spine should be obtained to evaluate the type of curvature of the spine. Magnetic resonance imaging may have to be performed in the coronal plane (in severe scoliosis) as well as in the sagittal plane to evaluate the cord. Even with the coronal plane, it may not be possible to adequately evaluate the cord and spinal canal with MRI. In these cases, water-soluble myelography with follow-up CT is the additional procedure of choice (Figure 1 1).
CONCLUSION Radiological modalities are extremely important in evaluating the postoperative child with a myelomeningocele. Depending on the age of the child, CT or ultrasound is used to evaluate ventricular size. Magnetic resonance imaging is the best modality to evaluate the posterior fossa and total spine. The cervicomedullary junction, Chiari II malformation, the degree of herniation of the hindbrain, hydromyelia, retethering, inclusion epidermoid, and lipoma can all be adequately
614
evaluated with MRI. At times, MRI may not adequately diagnose subtle cases of tethering, in which case real-time ultrasound to evaluate cord pulsations is the next modality. Subtle cases of diastematomyelia may not be adequately visualized on MRI even with the coronal and axial projections. In these cases, water-soluble myelography with CT is the best modality. At times, it may be difficult to differentiate a localized area of hydromyelia from an arachnoid cyst or cord atrophy. In this case, water-soluble myelography with CT should be used. In children who have severe scoliosis or kyphoscoliosis (in which an underlying cause may not be neuromuscular but may be secondary to retethering or hydromyelia) and if the MRI is not adequate to completely visualize the cord because of the severe nature of the scoliosis, then water-soluble myelography with CT should be instituted. An understanding of the clinical symptoms, associated disease entities, and complications that can occur in the child with a myelomeningocele will help the radiologist with accurate evaluation and diagnosis. Literature Cited 1. McLone DG. Treatment of myelomeningocele: arguments against selection. Clin Neurosurg. 1986;33:359-370. 2. McLone DG. Results of treatment of children with a myelomeningocele. Clin Neurosurg. 1983;30:407-412. 3. Naidich TP, Harwood-Nash DC, McLone DG. Radiology of spinal dysraphism. Clin Neurosurg. 1983;30:341-365. 4. Naidich TP, McLone DG. Congenital pathology of the spine and spinal cord. In: Taveras JM, Ferucci JT, eds. Radiology. Philadelphia, Pa: JB Lippincott Co; 1986:1-23. 5. Grant EG, White EM, Schellinger D, Choyke PL, Sarcone AL. Cranial duplex sonography of the infant. Radiology. 1987;163:177-185. 6. Naidich TP, McLone DG, Fulling KH. The Chiari malformation, part IV: the hindbrain deformity. Neuroradiology. 1983;30:179-197. 7. Naidich TP, Fernbach SK, McLone DG, Shkolnik A. Sonography of the caudal spine and back: congenital anomalies in children. AJNR. 1984;5:222-234.
JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
Seven hundred fifty-five children with myelomeningoceles were evaluated radiologically at the Children's Memorial Hospital in Chicago. From our material, we propose a diagnostic radiologic model to accurately evaluate the neurological problems in the myelomeningocele child. This model is based on the clinical symptoms in these children and the radiologic modalities of magnetic resonance imaging (MRI), computed tomography (CT), ultrasound, myelography, and plain radiographs. We found MRI to be the best modality to evaluate the posterior fossa and total spine. Computed tomography and ultrasound are used to evaluate ventricular size. At times MRI may not adequately diagnose subtle cases of tethering of the spinal cord, cord infarction, arachnoid cysts, or diastematomyelia. In these cases, further evaluation may be necessary with real time ultrasound to look at cord pulsations and water soluble myelography with follow through CT to differentiate cord infarction, arachnoid cyst, localized hydromyelia, or diastematomyeFrom the Division of Neuroimaging, Department of Radiology, Children's Memorial Hospital, Northwestern University Medical School, Chicago, Illinois. Requests for reprints should be addressed to Dr Sharon E. Byrd, Division of Neuroimaging, Department of Radiology, Children's Memorial Hospital, Northwestern University Medical School, 2300 Children's Plaza, Chicago, IL 60614. 608
lia. If MRI is not adequate to completely visualize the cord because of the severe nature of the scoliosis, then water soluble myelography with CT is indicated. (J Nati Med Assoc. 1991 ;83:608-61 4.) Key words * myelomeningocele * diagnosis * magnetic resonance * computed tomography ultrasound -
Between 6000 and 11 000 babies are born with a myelomeningocele each year in the United States. Over the last quarter of a century, a great deal of attention has been directed in the medical literature as to how to treat, manage, and evaluate these patients. At the Children's Memorial Hospital in Chicago, we have treated and managed more than 1000 patients with myelomeningoceles through an interdisciplinary health professional team. In our experience, an aggressive medical approach has resulted in a lower mortality rate and a better quality of survival for the majority of our myelomeningocele children. With an increasing awareness and acceptance of disabled children and adults in our society, we feel that it is imperative that these children with a myelomeningocele be managed aggressively.1 2 Because the underlying abnormality is the congenital malformation that affects the total neural axis, a myriad of neurological problems confront these children. We propose a diagnostic radiologic model to accurately evaluate the neurological problems in the child with a myelomeningocele based on the clinical symptoms and JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
EVALUATION OF MYELOMENINGOCELE
Radiologic Protocol Newborn With Unoperated Myelomeningocele (M/IM)
Symmetric neurologic deficits rule out hydrocephalus
I
US or CT (head)
Nl I,
Surgical repair of M/M with or without VP shunt
Severe asymmetric neurologic deficits rule out hemimyelocele
If
MR (head and spine or CT myelography)
Surgical repair
of M/M
Figure 1. Radiologic protocol for the newborn with unoperated myelomeningocele.
radiologic modalities of magnetic resonance imaging (MRI), computed tomography (CT), ultrasound, myelography, and plain radiographs. This radiologic model is designed to simplify and to determine which are the best radiologic tests to use in the neurologic evaluation of children with a myelomeningocele (Figures 1 and 2).
MATERIALS AND METHODS Over the past 3 years at the Children's Memorial Hospital in Chicago, we radiologically evaluated 300 children born with a thoracolumbar, lumbar, or lumbosacral myelomeningocele. Seventy-two of these children were evaluated before, and 300 children were evaluated after the myelomeningocele was repaired. They ranged in age from newborn to 17 years, and the sex predilection was 170 girls to 130 boys. The common symptoms were a back mass at birth (myelocele or myelomeningocele), hydrocephalus, headaches, lethargy, vomiting, apnea, stridor, paraparesis or paraplegia, deteriorating neurologic function, bladder and bowel incontinence, and scoliosis. The radiologic modalities used to evaluate the children consisted of CT, MRI, ultrasound, CT myelography, and plain radiographs of the spine. The CT scans were of the head, noncontrast studies, axial projection, 3-mm to 5-mm slice thickness, and contiguous table movement. The MRI scans were of the head (with an emphasis on the posterior fossa) and total spine in the sagittal projection performed with TI weighted JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
Radiologic Protocol
Repaired M/M Child A? Later deterioration Signs of t ICP of neurological hydrocephalus or functon Shunt mafunction I H (1) MR Head US wih indices or CT or MR MR (a) Braln to evaute for: 1. Dyspistc or hypoplastic stnhxres 2. C cdullary kInk for obsion, synngobulbia, amchnoid cyst 3. Hydrocephalus (b) Total spine to evaluate for: 1. Hydromyelia, a i cyst, atrophy 2. D ltmtolia 3. Tethering 4. Inclusion (epQdefnoids, lipomas. (2) AdJunct procedures to MR US of (a) spine to evaluate for: pulsations in subtle cases of tetheing (3) CT myelography
'I
(b) Arachnoid cyst, atrophic cord,
hydromyelia, diastematomyelia scoliosis, kyphoscoliosos (4) Plain lumbosacral radiographs
severe
(a) To evaluate severiy of scoliosis Figure 2. Radiologic protocol for the repaired myelomeningocele child.
spin echo (SE) pulse sequences with a repetition time (TR) of 500 to 600 milliseconds, and an echo time (TE) of 20 to 30 milliseconds. Axial TI weighted MRI scans through the lumbosacral area also were obtained routinely. The slice thickness was 3 mm to 5 mm without a gap or with a 0.5-mm gap. At times, additional pulse sequences proton density (SE, TR 2000/TE 30), T2 weighted (SE, TR 2000/TE 90), or gradient echo acquisitions T2* (TR 200-400/TE 20-30 and flip angle 100 to 150) were obtained as well as other projections axial or coronal through localized areas of the posterior fossa or spine. The matrix size was 256 x 609
EVALUATION OF MYELOMENINGOCELE
Figure 3. Ultrasound Doppler indices of the head (a,b) demonstrating measurement of the pulsatile index and resistive index of the anterior cerebral artery. Coronal ultrasound (c,d) of the head demonstrating hydrocephalus with dilated frontal and temporal horns (small arrows) and bodies (large arrows) of the lateral ventricles. 128 or 256 and the number of excitations were 1, 2, or 4. The ultrasound was of the head or lumbosacral spine using a real-time unit with 5 MHz or 3 MHz sector and linear-array transducers. The myelograms were performed with Tohexol (Omnipaque, Barceloneta, Puerto Rico) 180 or 240 with 2 mL to 10 mL injected into the thecal sac via a lumbar puncture lateral to the repair site with conventional filming and then always followed by an axial CT survey of the total spine immediately after the myelogram and with a delayed axial CT survey (4 to 6 hours later). Plain radiographs of the spine were performed conventionally with only anteroposterior (AP) and lateral projections. The equipment used was a GE 9800 (Milwaukee, Wisconsin) or Interad CT (Chicago, Illinois) scanner, 0.5T Elscint (Tel Aviv, Israel) or 1 .5T GE MRI (Milwaukee, Wisconsin) scanner, Accuson (Mountain View, California) real-time ultrasound scanners both with and without color doppler and conventional equipment for the myelograms and plain radiographs. The children were sedated when necessary for the CT or MRI studies with chloral hydrate 50 to 100 mg/kg orally with a maximumn of 2 g. Nembutal 2 mg/kg (TM), nubaine 0. 15 mg/kg (TM), and chloral hydrate 50 mg/kg were for the mylga T T
used
610
Figure 4. A newborn with a myelomeningocele
(arrow). signs were monitored with a pulse oximeter for the CT and myelogram CT and manually by a nurse in the room with the magnet for the MRI.
RESULTS AND DISCUSSION Depending on the symptoms, a baby born with a myelomeningocele may or may not require detailed radiological evaluation. The majority of newborns with an unoperated myelomeningocele have slightly asymmetric or symmetric neurologic deficits. These patients require urgent surgical repair of the myelomeningocele to prevent exacerbation of their handicaps or death.3 The only radiological role in these patients is to image the head to evaluate for hydrocephalus, via either ultrasound or CT (Figure 3). Depending on the degree of ventricular dilatation, the neurosurgeon may elect to shunt the ventricles at the same sitting as the repair of the myelomeningocele (Figure 4). Newborns with unoperated myelomeningoceles who exhibit severe asymmetric neurologic deficits will require more extensive imaging modalities in order to rule out a hemimyelocele (diastematomyelia).3 The first modality is MRI of the head and spine to evaluate the degree of ventricular dilatation as well as to evaluate the JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
EVALUATION OF MYELOMENINGOCELE
Figure 6. MRI sagittal brain scan (SE 500/20). (a) The small arrow indicates Chiari 11 with a diverticulum of the fourth ventricle, and the large arrow indicates an arachnoid cyst of the posterior fossa. (b) Chiari 11 and IV are indicated; a severely dysplastic posterior fossa with a thinned downward displaced brainstem and a marked hypoplastic cerebellum with only a nubbin of cerebral tissue present (arrow) are compatible with a Chiari IV.
Figure 5. MRI sagittal brain scan (SE 500/20). The arrow indicates Chiari 11 malformation with cervicomedullary kink at C2 to C3 level.
posterior fossa and total spinal axis to rule out a localized area of diastematomyelia. The MRI should be performed with TI-weighted images in sagittal and axial planes. If subtle abnormalities are seen, then further, more invasive procedures may have to be performed such as myelography CT to rule out partial or complete clefting of the cord and to locate the diastematic spur. The greatest radiological role is in evaluating the child postoperatively.3'4 Children who have had successful surgical repair should remain stable, and a few will go on to improve with a gain in some neurological functions. The child with a repaired myelomeningocele who starts to deteriorate is the child who requires greater radiological evaluation. In these cases, the whole neural axis should be imaged. However, depending on the symptoms, greater emphasis should be directed toward certain areas of the neural axis. The most common complications that these patients develop is hydrocephalus and shunt malfunction. Ninety-eight percent of patients with myelomeningoceles develop ventricular dilatation. Between 80% and 90% of these patients require shunt diversion of the cerebrospinal fluid (CSF).4 These patients commonly present with full fontanelle, rapidly increasing head circumference, and poor feeding (signs of increased intracranial pressure). Depending on the age of the JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
child, ultrasound of the head in children less than 1 year of age or a noncontrast CT scan in children over 1 year old should be used to evaluate the degree of ventricular dilatation. In infants who have or have not been shunted, the ultrasound with indices has proven to be a reliable index of increased intracranial pressure. The indices of the anterior cerebral artery are obtained and an increase in the pulsatile index and resistive index are used in conjunction with the size of the ventricular system on ultrasound to determine whether these children should be followed or shunted (Figure 3).5 Patients with myelomeningoceles have a 99% association with Chiari II malformation. This is a congenital anomaly of the hindbrain in which there is herniation of the medulla and at times the pons, fourth ventricle, and inferior aspect of the cerebellum into the upper cervical canal usually between C2 to C4 but the herniated contents may extend down to T 1.6 Patients with significant compression of hindbrain structures (brainstem) at the craniocervical junction or within the cervical canal may present with apnea, stridor, vomiting, poor tolerance to changes in food texture with choking, or respiratory distress.2 These symptoms may be due to significant compression of the hindbrain structures or to dysplasia of posterior fossa contents, which can also occur in patients having Chiari II malformation. The MRI is the first modality of choice in evaluating the posterior fossa and upper cervical canal. The sagittal TI -weighted images of the posterior fossa and upper cervical canal demonstrate the location of the cervicomedullary kink in 70% of the cases (Figure 5). It can also demonstrate whether there is an associated 611
EVALUATION OF MYELOMENINGOCELE
Figure 8. (a) CT axial scan. Scan taken after water-soluble lohexol myelogram with con trast material within subarachnoid space of the thoracic spine (small arrows) and within a large posterior intrathecal arachnoid cyst (large arrows) with displacement of the spinal cord (open arrow) anteriorly. (b) MRI axial scan (SE 500/20) of thoracic spine of the same patient as in 6a showing an arachnoid cyst (large arrow) of the same intensity as adjacent CSF of the thecal sac with anterior displacement of the cord (small arrow).
Figure 7. MRI sagittal scans (SE 600/30). (a) andAsaita Thoracic spine with (b) lumbar MR "bamboo" othtta therepir ite4 Ti.''!-wihe appearance to the cord are indicative of hy-
iw,
dromyelia. arachnoid cyst, hydromyelia, or syringobulbia involving the upper cervical cord, medulla, or craniovertebral junction. T2-weighted or gradient echo (T2*) views will help to determine the presence of CSF spaces (cisterns) at the level of the cervicomedullary kink. Depending on the degree of obstruction as manifested by no demonstration of CSF spaces around the cervicomedullary kink, either posterior fossa decompression may be necessary or shunting of the area of localized hydromyelia or syringobulbia. Also, at times the respiratory distress is secondary to dysplasia of posterior fossa structures, especially the medulla. The MRI will help to determine if a surgical condition exists (Figure 6). Patients who have an increase in scoliosis or a deterioration of neurological function such as increasing motor and sensory deficits within the lower extremities or bowel and bladder problems may have hydromyelia, arachnoid cyst, cord infarction with atrophy, diastematomyelia, or retethering of the spinal cord by scarring, inclusion epidermoids, or lipomas at
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Figure 9. (a) MRI axial scan (SE 500/20) of the lumbar spine showing diastematomyeliatwo spinal cords (arrows). (b) CT axial scan of upper thoracic spine with intrathecal lohexol demonstrating the two spinal cords (arrows)diastematomyelia.
spine is the first modality to evaluate these conditions. Between 20% and 60% of patients with myelomeningoceles may have hydromyelia. The area of hydromyelia may be focal, multiple, or diffuse extending throughout the total spinal cord. One of the first indications of a significant hydromyelia clinically is rapid progressive kyphoscoliosis. The hydromyelia may be secondary to hydrocephalus with resultant transmission of CSF through the obex down into the central canal and distention secondary to the increased hydrostatic pressure from above. Multiple diffuse areas of hydromyelia are usually easily identified on sagittal Tl MRI studies. If the "bamboo appearance" to the spinal cord is identified, this is classic for hydromyelia (Figure 7)s3d4 JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
EVALUATION OF MYELOMENINGOCELE
Figure 11. (a) Plain AP spine radiograph show ing levoscoliosis of thoracolumbosacral spine. (b) Coronal MRI scan (SE 600/30) illus trating suboptimal demonstration of the spin nal cord (arrows). (c) Water-soluble myelo gram demonstrating low-lying tethered cord (arrows) against right side of the spinal canal.
Figure 10. MRI sagittal thoracolumbosacral scan (SE 600/30) showing (a) spinal cord tethered at distal end by scar (arrow) at the repair site and (b) increased lordosis to the lumbosacral spine indicative of retethering. At surgery, the cord was tethered by scar along the posterior wall of the thecal sac in the lumbosacral area.
At times, it may be difficult to distinguish localized areas of hydromyelia from an arachnoid cyst or areas of localized cord atrophy secondary to cord infarction. An axial TI may help to differentiate cord atrophy from these other two conditions. Usually, more invasive studies are necessary to accurately differentiate these three conditions. A water-soluble myelogram with a follow-up CT will differentiate these conditions. In patients who have localized atrophy, the cord is small and within the center of the thecal sac. In children who have an arachnoid cyst, the cord would be displaced by a cystic mass that is easily identified on the CT myelogram. In patients who have hydromyelia, the delayed CT-myelogram study will demonstrate the water-soluble contrast material to be within the central portion of the spinal cord (Figure 8). Diastematomyelia occurs in 30% to 40% of patients with myelomeningoceles.3,4 The area of the diastematomyelia is at the site of the myelomeningocele in 20% of JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 83, NO. 7
the cases, cephalic to this site in 30%, and caudal to this site in 25%. In evaluating these children for diastematomyelia, the coronal MRI is the best projection. If a suspicious area is identified on the coronal projection, then axial views of this area should be obtained. However, the MRI is not as sensitive in detecting diastematomyelia, and if there is suspicion, then a water-soluble myelogram with follow-up CT should be obtained. This is the most sensitive test to adequately evaluate the spine for partial or complete clefting (Figure
9). One of the most common problems that occurs in the child with a myelomeningocele is retethering at the repaired site. This was extremely common when the older technique of repair was used without producing a sling to hold the cord away from the posterior wall of the repaired thecal sac.2'3 The sagittal TI MRI of the cord with additional axial Ti-weighted images through the repair site can adequately evaluate retethering in the majority of cases. The classical findings consist of a straightened, taut, bow-string cord with its distal end adherent to the posterior wall of the thecal sac along the repaired site. In addition, there may be irregularity of the distal cord blending into the repaired wall of the thecal sac. These are findings of tethering by scar formation. Another sign is increase in the lordosis of the lumbosacral canal at the level of the repair with adherence of the spinal cord to the posterior wall of the spinal canal at the apex of the lordosis (Figure 10). The cord also may be tethered by an inclusion epidermoid or lipoma at the repair site. The MRI will demonstrate a mass within the distal aspect of the thecal sac near the repair site. The cord will be taut, and its distal end will blend into the mass. If the mass is of a similar signal as adjacent cord, then it is an inclusion epidermoid. If it is bright on the TI-weighted images 613
EVALUATION OF MYELOMENINGOCELE
(the same signal as subcutaneous fat), then it is an inclusion lipoma. At times, it may be difficult to definitely diagnose retethering at which time real-time ultrasound to image cord pulsations is necessary. If there are absent pulsations of the cord at the repair site in the neutral position or if the back is flexed and the cord pulsations disappear, then these are signs of significant tethering of the cord.7 Scoliosis, kyphoscoliosis, gibbus deformity, and severe lordosis present significant problems in the repaired myelomeningocele child. The abnormal curvature of the spine may be due to untreated hydromyelia, tethering, neuromuscular imbalance, one or more hemivertebrae with congenital bars, or a special form of musculoskeletal imbalance secondary to coronal orientation of all of the paraspiral muscles and adjacent laminae at one or more levels of the spinal dysraphism.4 Depending on the severity of and location of the abnormal curvature, it may not be possible to adequately evaluate these children with only MRI. Plain radiographs of the spine should be obtained to evaluate the type of curvature of the spine. Magnetic resonance imaging may have to be performed in the coronal plane (in severe scoliosis) as well as in the sagittal plane to evaluate the cord. Even with the coronal plane, it may not be possible to adequately evaluate the cord and spinal canal with MRI. In these cases, water-soluble myelography with follow-up CT is the additional procedure of choice (Figure 1 1).
CONCLUSION Radiological modalities are extremely important in evaluating the postoperative child with a myelomeningocele. Depending on the age of the child, CT or ultrasound is used to evaluate ventricular size. Magnetic resonance imaging is the best modality to evaluate the posterior fossa and total spine. The cervicomedullary junction, Chiari II malformation, the degree of herniation of the hindbrain, hydromyelia, retethering, inclusion epidermoid, and lipoma can all be adequately
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evaluated with MRI. At times, MRI may not adequately diagnose subtle cases of tethering, in which case real-time ultrasound to evaluate cord pulsations is the next modality. Subtle cases of diastematomyelia may not be adequately visualized on MRI even with the coronal and axial projections. In these cases, water-soluble myelography with CT is the best modality. At times, it may be difficult to differentiate a localized area of hydromyelia from an arachnoid cyst or cord atrophy. In this case, water-soluble myelography with CT should be used. In children who have severe scoliosis or kyphoscoliosis (in which an underlying cause may not be neuromuscular but may be secondary to retethering or hydromyelia) and if the MRI is not adequate to completely visualize the cord because of the severe nature of the scoliosis, then water-soluble myelography with CT should be instituted. An understanding of the clinical symptoms, associated disease entities, and complications that can occur in the child with a myelomeningocele will help the radiologist with accurate evaluation and diagnosis. Literature Cited 1. McLone DG. Treatment of myelomeningocele: arguments against selection. Clin Neurosurg. 1986;33:359-370. 2. McLone DG. Results of treatment of children with a myelomeningocele. Clin Neurosurg. 1983;30:407-412. 3. Naidich TP, Harwood-Nash DC, McLone DG. Radiology of spinal dysraphism. Clin Neurosurg. 1983;30:341-365. 4. Naidich TP, McLone DG. Congenital pathology of the spine and spinal cord. In: Taveras JM, Ferucci JT, eds. Radiology. Philadelphia, Pa: JB Lippincott Co; 1986:1-23. 5. Grant EG, White EM, Schellinger D, Choyke PL, Sarcone AL. Cranial duplex sonography of the infant. Radiology. 1987;163:177-185. 6. Naidich TP, McLone DG, Fulling KH. The Chiari malformation, part IV: the hindbrain deformity. Neuroradiology. 1983;30:179-197. 7. Naidich TP, Fernbach SK, McLone DG, Shkolnik A. Sonography of the caudal spine and back: congenital anomalies in children. AJNR. 1984;5:222-234.
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