THE DIAGNOSIS OF CONGENITAL SPINAL DISORDERS IN COMPUTED TOMOGRAPHY (CT) Claus D. Claussen, Friedel W. Lobkamp and Ulricb Banniza v. Bazan
Claussen, CL D., Lohkamp, F. W. and Banniza v. Bazan, U'.: The diagnosis of congenital spinal disorders in computed tomography (CT). Neuropadiatrie 8: 405—417 (1977). 9 patients (8 girls, 1 boy) with dysraphic disorders of the spinal column were examined by CT. In 6 cases no diastematomyelia was established. Among the 8 girls, an intraspinal bony septum was identified in 7 instances and a splitting of the cord without identifiable septum was seen in 1 girl. In 6 patients with symptoms dysplastic changes of the cord independent of the segmental level could be identified, such as variable thickness and a heterogenous absorption pattern of the cord. Three girls with symptomless diastematomyelia showed no striking absorption pattern of the spinal cord. Asymptomatic diastematomyelia indicates that frequently concomitant orthopaedic and neurological disorders cannot be referred to a mechanically obstructed ascent of the cord alone, but infer complex etiologies, probably including abnormal medullary vascularization Dural sac and subarachnoid fixation of the spinal cord cannot be identified by CT. Unless there is a possibility of a low lumbar medullary conus or of spinal cord dysplasia or intraspinal lipoma, cyst or fistula, one can assume that the normal ascent of the cord is obstructed with subsequent pull on the cord elements. From our preliminary experience which takes into account conventional radiological procedures, the appropriate task of CT consists of identifying even a minimally calcified septum in radiologically suspected diastematomyelia. Further, with CT one can exclude a splitting of the cord without a calcified septum. CT provides a noninvasive method for assuring diagnosis of diastematomyelia at an early stage and enables one to make the differential diagnosis from pseudodiastematomyelia. Computerized tomography spinal cord myelodysplasia spina bifida
With computerised axial tomography (C.A.T.) it became possible to study radiologically, the vertebral canal and the spinal cord without the interference of superimposed shadows, Earlier, the study of various types of spinal dysraphism and of other developmental disorders required plain radiography, tomography and myelograReceived: June 29, 1977
diastematomyelia
dysraphic
phy with positive and negative contrast media, before appropriate treatment could be planned. Reports are now available in the use of C.A.T. in spinal dysraphism, concerning syringomyelia (1) and diastematomyelia (2). The present study deals with 9 patients, eight of them children suffering from spina bifida, who presented with
Accepted: Oct. 13, 1977
Address: Cl. D. C , Zentrum Radiologie, VofistraKe 3, D-6900 Heidelberg
405
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German Cancer Research Center, Institute of Nuclear Medicine, Department of Radiology and Orthopedic Clinic, University of Heidelberg
orthopaedic and neurolical problems related to their spinal lesion. Nine were female.
Pathology of diastematomyelia Diastematomyelia is a congenital disorder of the spinal cord and usually (but not always) of the vertebral column. I t is usually located in the thoraco-lumbar or lumbar region. The spinal cord is usually split into two hemi-cords, usually associated with a bony or fibro-cartilaginous septum arising from the dorsal surface of the vertebrae. Occasionally, the cord is split into more than two. The two cords often unite below the level of the septum. The pathological features of diastematomyelia consist of the following (3,4): a) spina bifida occulta, b) dilatation of the spinal canal at the level of a bony or cartilaginous septum, C) two hemicords enclosed by their own separate arachnoid membranes and in about half the cases in their own dura mater. In the other half a single dura mater covers both cords, d) the two hemicords are usually uneven in size and contain different amounts of cellular and neuronal substance (5). Nevertheless, the butterfly figure of the grey matter consists of two ventral and two dorsal columns, e) the normal ascent of the spinal cord is obstructed by the intraspinal septum (where this exists) and re-
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sults in traction of the cord and its roots. This can readily be seen at operation (4). Pressure effects are evident at the caudal end of the intramedullary cleft near the contact point between the spinal cord and the septum. Interference with the normal ascent of the cord may also be due to posterior dural bands and aberrant nerve roots, even in cases without a bony spur (5), f) diastematomyelia occurs in about 5OIo of cases with congenital scoliosis (6). Roentgenographic findings Only a brief summary of the radiological signs are described because several fuller accounts are available in the literature (4, 7, 8). The pathognomonic feature is a bony septum in the midline. I t can best be identified in the frontal projection and is seldom longer than 1.5 cm (7). Tomographically, the septum is identified as a line of interruption where the septum is attached. When the septum is only slightly calcified or when the spinal column is severly deformed, a tentative diagnosis of diastematomyelia can be made by C.A.T. With this technique associated anomalies of the vertebral bodies and the arches are more distinctly demonstrable. Concomitant anomalies are a shortening of the sagittal anteroposterior diameter at the level of the septum, a partial or complete sagittal cleft of the vertebral bodies, and hemivertebrae or vertebral agenesia. The anomalies of the spinal column may extend over
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Claussen et al.
several adjacent segments. The widening of the interpedicular distance present in a high percentage of cases, reaches its maximum in the region of the septum. In segmentation failures the combination of an intersegmental fusion of the laminae with spina bifida is a more reliable diagnostic indication of the level of the septum than cutaneous manifestations of anomalous development of the vertebral bodies (4). In about 50°/o of cases the septum is either not at all or very slightly ossified (3). In such cases myelography is necessary for the diagnosis. The septum appears as a nearly round or oval area devoid of contrast material in or next the middle of the dural sac. That myelographic filling defect may be due to a fibrous band, a kartilaginous or bony septum. The dural sac is usually split into two contrast columns. Myelographic filling defects may appear as artefacts and make the interpretation of findings considerably more difficult; for identifying defects caused by a splitting of the cord larger amounts of contrast media and radiographs in prone and supine position have proved useful (4).
Clinical features The clinical features are variable and may involve the skin, the skeleton, the nervous system or the sphincters. The cutaneous changes include a dorsal hairy patch over the spine, naevi, or a median cutaneous lipoma over which there is usually a painless dimple. Cutaneous sinuses or fistulous tracks
may also be seen, these being the remnants of the primitive neurenteric canal. The skeletal abnormalities consist of foot deformities, such as pes varus or valgus, weakness of one or both legs, difference between the length of the legs of scoliosis. These may lead to delayed walking or abnormalities of the gait, which may be slight or severe. According to Hilal (4) in untreated diastematomyelia scoliosis is more frequent and is progressive. The brain may be affected by "dysraphic equivalents" such as stenosis due to gliosis of the aqueduct or an Arnold-Chiari malformation. Open encephalocele or spina bifida may co-exist. Present material. Method of study To localise the vertebral segmental level, first plastic tubes filled with contrast medium were attached to the skin as markers, then a survey radiograph was taken and finally the abnormal part of the spinal column was examined in sections while the patient remained in the same position. In children with orthopaedic or neurological symptoms C.A.T. of the head was also performed to detect any hydrocephalus or other intracerebral anomaly. All investigations were carried out by the Fa. Delta Ohio Nuclear whole body scanner, without injecting contrast medium into the subarachnoid space. With a matrix of 256 X 256 picture elements and an object diameter of 40 cm. The minimal spatial resolution was 1.5 X 1.5 X 13 mm and the section thickness was 13 mm.
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Fig 1 Transverse section a ) At L5: tongue-shaped cross-sections of spinal cord; condition after resection of a lumbosacral myelomeningocele, 6 ) at L213: parabola-shaped cross-section of spinal cord, near the vertebral body with rounded area of low absorption, c) at L1: bony septum, d) at T 11: band-shaped, flat cross section of the cord
The patients Nine patients were studied. More detailed description of the C.A.T. find-
ings in five symptomatic and two asymptomatic children who had radiologically definite or suspected midline spur is given below.
Case reports Case 1
Aged 8 years. Clinical condition: a lumbo-sacral myelomeningocele had been repaired. The child was paralysed below S1/S2 and did not walk until three years of age. There was vertical talus with bilateral pes valgus, more severe on the left. Hydrocephalus was treated with a Pudenz-Heyer shunt which was frequently revised. There was urinary and faecal incontinence and a pelvic kidney. Radiograph of the vertebrae showed wide cleft extending from LI to the sacrum with a probable midline spur at L2. CT-findings (Fig. 1): dorsoventral septum at L2 12 mm long and 8 mm wide. At different segmental levels cross sections of the spinal cord were abnormal with preponderantly rounded low density areas. At the level of the septum, near to the vertebral column, the cross section of the cord was parabola shaped. At T 11 level the cord was band shaped and flat. Case 2
Aged 5 years. The child's thoracolumbar meningomyelocele had been resected and she was paralysed. Probably urinary and faecal incontinence. Radiograph of the spine showed a cleft extending from T 12 to the sacrum. There were wedge-shaped vertebrae with a suspicion of diastematomyelia at L1. CT findings (Fig. 2): intraspinal bony septum at L1, 16 mm long and 8 mm wide. Its X-ray absorption values
of 75 to 121 Delta units1 were significantly lower than the bone absorption values (approx. 300 Delta units). The segment of the spinal cord close to the caudal end of the bony septum was distended with a substance with increased absorption values in some and with low values in other places. At the level of the conus and of the lowly sited cauda equina there was a diagonally running strip of low X-ray absorption. Brain scan showed porencephaly of the anterior horn of the right ventricle. Case 3
Aged 4 years. Clinical condition: resected meningomyelocele with foot deformity and urinary and faecal incontinence. Radiograph of the spine: spina bifida at LlIL2. C T findings (Fig. 3): At L2 intramedullary rounded area of low absorption in the peripheral part (2 o' clock) whi& is limited by an area equivalent to X-ray absorption of calcium. At LlIL2 the cross section of the cord appears ring-shaped as a result of a large, central low density area. At L1 several circular low density areas (not equivalent to cerebro-spinal fluid density!) can be defined peripherally low absorption values in places. No intraspinal septum, no splitting of the cord. The findings indicate a dysraphic dysplasia of the spinal cord associated with fixation. 1 A Delta unit is an arbitrary index of radiation absorption based on a scale of: air = -1000, water = 0, bone = +lo00
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Fig. 2 Transverse section a ) At L5: low lumbar medullary conus with band-shaped zone of low absorption running diagonally. b) Distended cord: cross-section at LllL2, with increased absorption values in some places and low values in others. Bony septum dorsally attached to the vertebral body. c) At L l : intraspinal bony septum 16 rnm long and max. 8 rnm wide, with heterogeneous pattern, significant low absorption of the bone compared with the density of the vertebral body
Case 4
Aged 8 years. Lumbosacral lipoma, about first-sized, with central dimpleshaped skin retraction. Intermittent urinary and faecal incontinence, since 3 years increasing foot deformity like a club foot. Radiograph: Cleft in the lumbar spine extending from L3 to sacrum. C T findings (Fig. 4): Within the vertebral canal posteriorly to the spinal cord absorption values can be measur-
ed which correspond to those for subcutaneous fat
Aged 12 years. No neurological deficit. Radiograph: Midline spur at Th 11. Spina bifida extending from Th 11 to sacmmCT findings (Fig. 5): At Th 11 intraspinal bony septum about 16 mm long and max. 4 mm wide; at Th 11/12 inconspicously shaped, normal absorption values of the cord.
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Fig. 3 Transverse section a) At L2: intramedullary low density area, peripherally (2 o'clock) defined by an area with density of calcium. The vertebral body partly sectioned appears illd,tfined. b) At L1: several circular low-density areas (not corresponding to cerebrospinal density) intramedullary, peripherally definable with increased absorption values in places
Case 6
Aged 12 years (Fig. 6): Congenital scoliosis. Radiograph: Diastematomyelia at L1. Myelographically typical splitting of the cord above and below the bony septum. CT findings (Figs. 6a, 6b): At L5 low lumbar transitional region of conus / cauda. Bony septum at L3 (about 12 mm long and 2 mm wide).
Discussion The nine patients examined by CT for diastematomyelia comprised 7 children, 1 adolescent and 1 adult. Of the 8 patients diastematomyelia, had an intraspinal bony septum ing ventrodorsally max. l6 mm long and 8 mm wide. In 2 girls
'
Fig. 4 Transverse section a t ~ 4 / 5 :posterior to the spinal cord a circular part of intraspinal tissue with absorption values corresponding to density of fatty tissue. No &gnificant absorption pattern of the low-lumbar medullary conus
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Fig. > Diastematomyelia with bony septum at T 11, a) Radiograph, b) CT-scan, c ) Inconspicuously shaped cord, with no striking absorption pattern
with bony septum (cases 1 and 2 ) , a meningomyelocele was resected after birth and a ventricular shunt implanted. In one case the meningomyelocele was not operated after birth because of the unfavourable prognosis. In 3 of 7 cases the dia~tematom~elia with bony septum remained symptomless. The following changes could be established by CT: In our cases the bony septums were located around L1 and ran dorso-
ventrally obliquely in a widened spinal canal. The cords on both sides of the septum usually can be distinguished one from another. In one case a gap of about 2 mm width was present near the anterior and posterior end of the bony septum. As C T is highly sensitive to calcium containing deposits, the gap must be a true interruption of the bony septum. Probably it represents an interruption line of the bony septum at the contact points as reported by Hilal as
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well. Hilal finds evidence for an isolated ossification centre of the bony septum that is separate from the remainder vertebral body and arch. With 6 children and 1 adolescent with dia~tematom~elias,and 1 child without spur - or split cord, dysplastic alterations of the spinal cord were revealed by CT. These alterations were characterized by a variable thickness of the spinal cord and were independent of the segment level, usually associated with intramedullary low-density areas, or an inhomogeneous absorption pattern of the cord. Patho-anatomically, the inhomogeneous absorption values of the cord associated with dysraphic myelodysplasia may correspond to gliosis or fibrous replacement of neutral tissue, possibly as a result of focal damage and a nonspecific reaction of embryonic tissue to teratogenic influences. By means of tissue absorption measurements various tissues with X-ray absorption values due to different physical and chemical conditions can be differentiated to a certain degree. The strikingly low radiation absorption of fat tissue figures about -'0° to on the scans is practical value in the diagnosis of intraspinal lipoma. Thus the absorption measuremerits in case 4 produced intraspinal absorption values which corresponded to those of subcutaneous fat tissue. In the same way intraspinal fluid containing cysts may well be defined according to their low X-ray absorption values. These measurements are particularly useful to diagnose intraspinal cysts
Fig. 6 a / Transverse section a t L5 through the low lumbar transitional region of conusl cauda. 6) Bony septum at L3. c) Myelogram and tomography: splitting of the cord from about 3 cm above to about 2 cm below the bony septum
that frequently occur (9), i.e. extradural cystic herniations of the arachnoid and less frequently, cystic teratomas and enterogenous cysts which may be as-
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Fig. 6 c
sociated with spina bifida. Because of the high sensitivity of CT. to calcium a minimally calcified septum can be seen, which cannot be identified on conventional radiographs. In the same way, an intramedullary cleft with its low density can be recognized. Although CT enables to assess intraspinal structures morphologically and quantitively, it has the disadvantage of lower spatial resolution than conven-
tional radiological techniques. Thus the spatial resolution is not sufficient to identify a fixation of the spinal cord in a foetal position, resulting from fibrous bands or attached arachnoid membranes near the bony septum or the low lumbar medullary conus. T o diagnose fixation of the spinal cord due to dural bands or adhesions it is necessary to use myelography, because of its greater capacity for recognizing fine
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details. Nevertheless, the dural bands and the adhesions cannot be defined directly on the myelogram. Artefacts can make the identification of findings considerably more difficult: with air myelography a vertical radiolucent line can appear, due to air collection (8) in a deep central anterior fissure, simulating a splitting of the cord; even a sufficiently strong cerebrospinal fluid surface tension between the cord elements and the posterior meninges has been described as the cause of a dorsally fixed cord not revealed by surgery. This fixation was diagnosed by air myelagraphy because of lack of mobility of the spinal cord thought to be shown by radiographs taken during movement from the supine to the prone position. From this, it emerges that the differentiation of diasternatomyelia from pseudodiastematomyelia when applying conventional radiological procedures may cause ~roblemsin interpretation. By locating even a minimally calcified septum or intramedullary cleft with the help of the noninvasive CT, the diagnosis of diastematomyelia is appreciably improved. For early recognition of diastematomyelia and subsequent surgical treatment in children suffering from orthopaedic and neurological symptoms of spinal dysraphism and associated grosser anomalies the following radiological procedure should be carried out: 1. Survey radiograph of the spinal column. 2. If a diastematomyelia cannot be diagnosed definitely by I., then CT should be applied before a myelo-
g-aphy. In particular, the medullary conus must be specially studied in order not to overlook a fixation caused by lipoma or a malformation. Linear tomography with its well-known possibilities for false evidence by striped blurring shades, will hardly be necessary for identifying a calcified intraspinal septum. The mechanical obstruction of the medullary ascent by dural or arachnoid adhesion in the region of the septum or conus requires early diagnosis of diasternatomyelia and prompt operative measures in order to avoid progressive orthopaedic damage and neurological deficits caused by a drag on the spinal cord. Because congenital scoliosis frequently coincides with diastematom~elia,this must first be excluded because measures taken to correct the scoliosis may result in neurological damage, such as paresis of the legs (10). In this context it must be emphasized that a diasternatomyelia can remain symptomless. The asymptomatic cases with a low lumbar fixed conus suggest that the fixation of the cord in diasternatomyelia with subsequent development of symptoms may not only be caused by traction or pressure effects on the cord, but also by other factors including abnormal vascularization, i. e. stenosis of the arterial spinal axes. C T of lumbar and dorsal spines revealed no definite macroscopic dysplastic changes of the cord. Where a diastematomyelia shows spinal cord changes demonstrated by CT, a fixation of the cord seems more likely than in the absence of such changes.
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Zusammenfassung
Es wurden 9 Patienten (8 Madchen, 1 Junge) mit dysrhaphischen Storungen der Wirbelsaule und rontgenologisch in 6 Fallen nicht eindeutig nachweisbarer Diastematomyelie computertomographisch untersucht. I n 8 Fdlen - ausschliel3lich Madchen - liei3 sich im Computertomogramm 7mal eindeutig ein kalzifiziertes, intras~inalesKnochenseptum und einma1 eine Zweiteilung des Ruckenmarkes ohne erkennbares Septum nachweisen. Bei allen Patienten mit klinischer Symptomatik konnten dysplastische, von der Segmenthohe unabhangige Markveranderungen, wie Kaliberschwankungen und ein heterogenes Absorptionsmuster der Medulla, nachgewiesen werden. Drei Madchen rnit klinisch symptomloser Diastematomyelie zeigten computertomographisch kein auffalliges Absorptionsmuster des Ruckenmarkes. Asymptomatische Diastematomyelien weisen darauf hin, dai3 die gewohnlich begleitenden orthopadischen und ne~rolo~ischen Storungen ursachlich nicht allein auf eine mechanische Behinderung des Ascensus medullae zuriickgefuhrt werden konnen, sondern durch eine komplexe Atiologie einschliei3lich medullarer Vaskularisationsstorungen bedingt sind. Eine durale bzw. subarachnoidale Fixation des Riickenmarkes 1Zi3t sich computertomographisch direkt nicht nachweisen. Nur bei computertomographischen Hinweisen auf einen tiefstehenden Conus medullaris, Markdysplasien, intraspinale Lipome, Zysten
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oder Fisteln ist mit groi3er Wahrscheinlichkeit ein mechanisch behinderter Ascensus medullae mit Zugbeanspruchung der nervalen Strukturen anzunehmen. Die methodisch adaquate Aufgabe der C~m~utertomographie in der Diagnostik der Diastematomyelie und Markdysplasie besteht nach unseren bisherigen Erfahrungen bei Beriicksichtigung der herkommlichen radiologischen Untersuchungsmethoden darin, bei rontgenologischem Verdacht auf eine Diastematomyelie auch ein minimal kalzifiziertes Septum definitiv nachzuweisen, eine medullare Zweiteilung ohne Knochenseptum und begleitende grobere Anomalien auszuschliei3en sowie als nicht invasive Methode zur friihzeitigen diagnostischen Sicherung der Diastematomyelie und zum Ausschlufl differentialdiagnostischen einer Pseudodiastematomyelie beizutragen.
References Di Chiro, G., Axelbaum, S. P., Schellinger, D. et al.: Computerized axial tomography in syringomyelia. N. Engl. J. Med. 292: 13-16 (1975). Weinstein, M. A., Rothner, A. D., Duschesneau, P., Dohn, D. F.: Computed tomography in diastematomyelia. Radiology 117: 609-611 (1975). Herren, R. Y., Eduards, J. E.: Dystomyclia (duplication of the spinal cord). Arch. Path. 30: 1203-1214 (1940). Hilal, S. K., Marton, D., Pollack, E.: Diastematomyelia in Children. Radiology 112: 609-621 (1974). James, C. C. M., Lassman, L. P.: Spinal Dysraphism. New York: Appleton-Century-Crofts 1972. Winter, R. B., Haven, J. J., Moe, J. H. et al.: Diastematomyelia and congenital spine
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9. Rand, R. W., Rand, C. W.: Epidermoids, dermoids and dermal sinuses. Extradural spinal cysts. In: Intraspinal Tumors of Childhood, 348-381 and 425-446, by R. W. and C. W. Rand, ThomasISpringfield, Ill. 10. Vandresse, J. H. and Cornelis, G.: Report of eight Observations. Neuroradiology 10: 87-93 (1975).
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deformities. J. Bone Joint Surgery 56: 2739 (1974). 7. Neuhauser, E. B. D., Wittenborg, M. H., Dehlinger, K.: Diastematomyelia: transfixation of the cord or cauda eauina with congenital anomalies of the spine. Radiology 54: 659-664 (1950). 8. Scatliff, J. H., Till, K., Hoare, R. D.: Incomplete, false and true Diastematomyelia. Radiology 116: 349-354 (1975).
Claussen, CL D., Lohkamp, F. W. and Banniza v. Bazan, U'.: The diagnosis of congenital spinal disorders in computed tomography (CT). Neuropadiatrie 8: 405—417 (1977). 9 patients (8 girls, 1 boy) with dysraphic disorders of the spinal column were examined by CT. In 6 cases no diastematomyelia was established. Among the 8 girls, an intraspinal bony septum was identified in 7 instances and a splitting of the cord without identifiable septum was seen in 1 girl. In 6 patients with symptoms dysplastic changes of the cord independent of the segmental level could be identified, such as variable thickness and a heterogenous absorption pattern of the cord. Three girls with symptomless diastematomyelia showed no striking absorption pattern of the spinal cord. Asymptomatic diastematomyelia indicates that frequently concomitant orthopaedic and neurological disorders cannot be referred to a mechanically obstructed ascent of the cord alone, but infer complex etiologies, probably including abnormal medullary vascularization Dural sac and subarachnoid fixation of the spinal cord cannot be identified by CT. Unless there is a possibility of a low lumbar medullary conus or of spinal cord dysplasia or intraspinal lipoma, cyst or fistula, one can assume that the normal ascent of the cord is obstructed with subsequent pull on the cord elements. From our preliminary experience which takes into account conventional radiological procedures, the appropriate task of CT consists of identifying even a minimally calcified septum in radiologically suspected diastematomyelia. Further, with CT one can exclude a splitting of the cord without a calcified septum. CT provides a noninvasive method for assuring diagnosis of diastematomyelia at an early stage and enables one to make the differential diagnosis from pseudodiastematomyelia. Computerized tomography spinal cord myelodysplasia spina bifida
With computerised axial tomography (C.A.T.) it became possible to study radiologically, the vertebral canal and the spinal cord without the interference of superimposed shadows, Earlier, the study of various types of spinal dysraphism and of other developmental disorders required plain radiography, tomography and myelograReceived: June 29, 1977
diastematomyelia
dysraphic
phy with positive and negative contrast media, before appropriate treatment could be planned. Reports are now available in the use of C.A.T. in spinal dysraphism, concerning syringomyelia (1) and diastematomyelia (2). The present study deals with 9 patients, eight of them children suffering from spina bifida, who presented with
Accepted: Oct. 13, 1977
Address: Cl. D. C , Zentrum Radiologie, VofistraKe 3, D-6900 Heidelberg
405
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German Cancer Research Center, Institute of Nuclear Medicine, Department of Radiology and Orthopedic Clinic, University of Heidelberg
orthopaedic and neurolical problems related to their spinal lesion. Nine were female.
Pathology of diastematomyelia Diastematomyelia is a congenital disorder of the spinal cord and usually (but not always) of the vertebral column. I t is usually located in the thoraco-lumbar or lumbar region. The spinal cord is usually split into two hemi-cords, usually associated with a bony or fibro-cartilaginous septum arising from the dorsal surface of the vertebrae. Occasionally, the cord is split into more than two. The two cords often unite below the level of the septum. The pathological features of diastematomyelia consist of the following (3,4): a) spina bifida occulta, b) dilatation of the spinal canal at the level of a bony or cartilaginous septum, C) two hemicords enclosed by their own separate arachnoid membranes and in about half the cases in their own dura mater. In the other half a single dura mater covers both cords, d) the two hemicords are usually uneven in size and contain different amounts of cellular and neuronal substance (5). Nevertheless, the butterfly figure of the grey matter consists of two ventral and two dorsal columns, e) the normal ascent of the spinal cord is obstructed by the intraspinal septum (where this exists) and re-
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sults in traction of the cord and its roots. This can readily be seen at operation (4). Pressure effects are evident at the caudal end of the intramedullary cleft near the contact point between the spinal cord and the septum. Interference with the normal ascent of the cord may also be due to posterior dural bands and aberrant nerve roots, even in cases without a bony spur (5), f) diastematomyelia occurs in about 5OIo of cases with congenital scoliosis (6). Roentgenographic findings Only a brief summary of the radiological signs are described because several fuller accounts are available in the literature (4, 7, 8). The pathognomonic feature is a bony septum in the midline. I t can best be identified in the frontal projection and is seldom longer than 1.5 cm (7). Tomographically, the septum is identified as a line of interruption where the septum is attached. When the septum is only slightly calcified or when the spinal column is severly deformed, a tentative diagnosis of diastematomyelia can be made by C.A.T. With this technique associated anomalies of the vertebral bodies and the arches are more distinctly demonstrable. Concomitant anomalies are a shortening of the sagittal anteroposterior diameter at the level of the septum, a partial or complete sagittal cleft of the vertebral bodies, and hemivertebrae or vertebral agenesia. The anomalies of the spinal column may extend over
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several adjacent segments. The widening of the interpedicular distance present in a high percentage of cases, reaches its maximum in the region of the septum. In segmentation failures the combination of an intersegmental fusion of the laminae with spina bifida is a more reliable diagnostic indication of the level of the septum than cutaneous manifestations of anomalous development of the vertebral bodies (4). In about 50°/o of cases the septum is either not at all or very slightly ossified (3). In such cases myelography is necessary for the diagnosis. The septum appears as a nearly round or oval area devoid of contrast material in or next the middle of the dural sac. That myelographic filling defect may be due to a fibrous band, a kartilaginous or bony septum. The dural sac is usually split into two contrast columns. Myelographic filling defects may appear as artefacts and make the interpretation of findings considerably more difficult; for identifying defects caused by a splitting of the cord larger amounts of contrast media and radiographs in prone and supine position have proved useful (4).
Clinical features The clinical features are variable and may involve the skin, the skeleton, the nervous system or the sphincters. The cutaneous changes include a dorsal hairy patch over the spine, naevi, or a median cutaneous lipoma over which there is usually a painless dimple. Cutaneous sinuses or fistulous tracks
may also be seen, these being the remnants of the primitive neurenteric canal. The skeletal abnormalities consist of foot deformities, such as pes varus or valgus, weakness of one or both legs, difference between the length of the legs of scoliosis. These may lead to delayed walking or abnormalities of the gait, which may be slight or severe. According to Hilal (4) in untreated diastematomyelia scoliosis is more frequent and is progressive. The brain may be affected by "dysraphic equivalents" such as stenosis due to gliosis of the aqueduct or an Arnold-Chiari malformation. Open encephalocele or spina bifida may co-exist. Present material. Method of study To localise the vertebral segmental level, first plastic tubes filled with contrast medium were attached to the skin as markers, then a survey radiograph was taken and finally the abnormal part of the spinal column was examined in sections while the patient remained in the same position. In children with orthopaedic or neurological symptoms C.A.T. of the head was also performed to detect any hydrocephalus or other intracerebral anomaly. All investigations were carried out by the Fa. Delta Ohio Nuclear whole body scanner, without injecting contrast medium into the subarachnoid space. With a matrix of 256 X 256 picture elements and an object diameter of 40 cm. The minimal spatial resolution was 1.5 X 1.5 X 13 mm and the section thickness was 13 mm.
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Fig 1 Transverse section a ) At L5: tongue-shaped cross-sections of spinal cord; condition after resection of a lumbosacral myelomeningocele, 6 ) at L213: parabola-shaped cross-section of spinal cord, near the vertebral body with rounded area of low absorption, c) at L1: bony septum, d) at T 11: band-shaped, flat cross section of the cord
The patients Nine patients were studied. More detailed description of the C.A.T. find-
ings in five symptomatic and two asymptomatic children who had radiologically definite or suspected midline spur is given below.
Case reports Case 1
Aged 8 years. Clinical condition: a lumbo-sacral myelomeningocele had been repaired. The child was paralysed below S1/S2 and did not walk until three years of age. There was vertical talus with bilateral pes valgus, more severe on the left. Hydrocephalus was treated with a Pudenz-Heyer shunt which was frequently revised. There was urinary and faecal incontinence and a pelvic kidney. Radiograph of the vertebrae showed wide cleft extending from LI to the sacrum with a probable midline spur at L2. CT-findings (Fig. 1): dorsoventral septum at L2 12 mm long and 8 mm wide. At different segmental levels cross sections of the spinal cord were abnormal with preponderantly rounded low density areas. At the level of the septum, near to the vertebral column, the cross section of the cord was parabola shaped. At T 11 level the cord was band shaped and flat. Case 2
Aged 5 years. The child's thoracolumbar meningomyelocele had been resected and she was paralysed. Probably urinary and faecal incontinence. Radiograph of the spine showed a cleft extending from T 12 to the sacrum. There were wedge-shaped vertebrae with a suspicion of diastematomyelia at L1. CT findings (Fig. 2): intraspinal bony septum at L1, 16 mm long and 8 mm wide. Its X-ray absorption values
of 75 to 121 Delta units1 were significantly lower than the bone absorption values (approx. 300 Delta units). The segment of the spinal cord close to the caudal end of the bony septum was distended with a substance with increased absorption values in some and with low values in other places. At the level of the conus and of the lowly sited cauda equina there was a diagonally running strip of low X-ray absorption. Brain scan showed porencephaly of the anterior horn of the right ventricle. Case 3
Aged 4 years. Clinical condition: resected meningomyelocele with foot deformity and urinary and faecal incontinence. Radiograph of the spine: spina bifida at LlIL2. C T findings (Fig. 3): At L2 intramedullary rounded area of low absorption in the peripheral part (2 o' clock) whi& is limited by an area equivalent to X-ray absorption of calcium. At LlIL2 the cross section of the cord appears ring-shaped as a result of a large, central low density area. At L1 several circular low density areas (not equivalent to cerebro-spinal fluid density!) can be defined peripherally low absorption values in places. No intraspinal septum, no splitting of the cord. The findings indicate a dysraphic dysplasia of the spinal cord associated with fixation. 1 A Delta unit is an arbitrary index of radiation absorption based on a scale of: air = -1000, water = 0, bone = +lo00
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1 Neuropidiatrie
Fig. 2 Transverse section a ) At L5: low lumbar medullary conus with band-shaped zone of low absorption running diagonally. b) Distended cord: cross-section at LllL2, with increased absorption values in some places and low values in others. Bony septum dorsally attached to the vertebral body. c) At L l : intraspinal bony septum 16 rnm long and max. 8 rnm wide, with heterogeneous pattern, significant low absorption of the bone compared with the density of the vertebral body
Case 4
Aged 8 years. Lumbosacral lipoma, about first-sized, with central dimpleshaped skin retraction. Intermittent urinary and faecal incontinence, since 3 years increasing foot deformity like a club foot. Radiograph: Cleft in the lumbar spine extending from L3 to sacrum. C T findings (Fig. 4): Within the vertebral canal posteriorly to the spinal cord absorption values can be measur-
ed which correspond to those for subcutaneous fat
Aged 12 years. No neurological deficit. Radiograph: Midline spur at Th 11. Spina bifida extending from Th 11 to sacmmCT findings (Fig. 5): At Th 11 intraspinal bony septum about 16 mm long and max. 4 mm wide; at Th 11/12 inconspicously shaped, normal absorption values of the cord.
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Fig. 3 Transverse section a) At L2: intramedullary low density area, peripherally (2 o'clock) defined by an area with density of calcium. The vertebral body partly sectioned appears illd,tfined. b) At L1: several circular low-density areas (not corresponding to cerebrospinal density) intramedullary, peripherally definable with increased absorption values in places
Case 6
Aged 12 years (Fig. 6): Congenital scoliosis. Radiograph: Diastematomyelia at L1. Myelographically typical splitting of the cord above and below the bony septum. CT findings (Figs. 6a, 6b): At L5 low lumbar transitional region of conus / cauda. Bony septum at L3 (about 12 mm long and 2 mm wide).
Discussion The nine patients examined by CT for diastematomyelia comprised 7 children, 1 adolescent and 1 adult. Of the 8 patients diastematomyelia, had an intraspinal bony septum ing ventrodorsally max. l6 mm long and 8 mm wide. In 2 girls
'
Fig. 4 Transverse section a t ~ 4 / 5 :posterior to the spinal cord a circular part of intraspinal tissue with absorption values corresponding to density of fatty tissue. No &gnificant absorption pattern of the low-lumbar medullary conus
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Spinal disorders in computed tomography
1 Neuropldiatrie
Fig. > Diastematomyelia with bony septum at T 11, a) Radiograph, b) CT-scan, c ) Inconspicuously shaped cord, with no striking absorption pattern
with bony septum (cases 1 and 2 ) , a meningomyelocele was resected after birth and a ventricular shunt implanted. In one case the meningomyelocele was not operated after birth because of the unfavourable prognosis. In 3 of 7 cases the dia~tematom~elia with bony septum remained symptomless. The following changes could be established by CT: In our cases the bony septums were located around L1 and ran dorso-
ventrally obliquely in a widened spinal canal. The cords on both sides of the septum usually can be distinguished one from another. In one case a gap of about 2 mm width was present near the anterior and posterior end of the bony septum. As C T is highly sensitive to calcium containing deposits, the gap must be a true interruption of the bony septum. Probably it represents an interruption line of the bony septum at the contact points as reported by Hilal as
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well. Hilal finds evidence for an isolated ossification centre of the bony septum that is separate from the remainder vertebral body and arch. With 6 children and 1 adolescent with dia~tematom~elias,and 1 child without spur - or split cord, dysplastic alterations of the spinal cord were revealed by CT. These alterations were characterized by a variable thickness of the spinal cord and were independent of the segment level, usually associated with intramedullary low-density areas, or an inhomogeneous absorption pattern of the cord. Patho-anatomically, the inhomogeneous absorption values of the cord associated with dysraphic myelodysplasia may correspond to gliosis or fibrous replacement of neutral tissue, possibly as a result of focal damage and a nonspecific reaction of embryonic tissue to teratogenic influences. By means of tissue absorption measurements various tissues with X-ray absorption values due to different physical and chemical conditions can be differentiated to a certain degree. The strikingly low radiation absorption of fat tissue figures about -'0° to on the scans is practical value in the diagnosis of intraspinal lipoma. Thus the absorption measuremerits in case 4 produced intraspinal absorption values which corresponded to those of subcutaneous fat tissue. In the same way intraspinal fluid containing cysts may well be defined according to their low X-ray absorption values. These measurements are particularly useful to diagnose intraspinal cysts
Fig. 6 a / Transverse section a t L5 through the low lumbar transitional region of conusl cauda. 6) Bony septum at L3. c) Myelogram and tomography: splitting of the cord from about 3 cm above to about 2 cm below the bony septum
that frequently occur (9), i.e. extradural cystic herniations of the arachnoid and less frequently, cystic teratomas and enterogenous cysts which may be as-
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Fig. 6 c
sociated with spina bifida. Because of the high sensitivity of CT. to calcium a minimally calcified septum can be seen, which cannot be identified on conventional radiographs. In the same way, an intramedullary cleft with its low density can be recognized. Although CT enables to assess intraspinal structures morphologically and quantitively, it has the disadvantage of lower spatial resolution than conven-
tional radiological techniques. Thus the spatial resolution is not sufficient to identify a fixation of the spinal cord in a foetal position, resulting from fibrous bands or attached arachnoid membranes near the bony septum or the low lumbar medullary conus. T o diagnose fixation of the spinal cord due to dural bands or adhesions it is necessary to use myelography, because of its greater capacity for recognizing fine
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Claussen et al.
details. Nevertheless, the dural bands and the adhesions cannot be defined directly on the myelogram. Artefacts can make the identification of findings considerably more difficult: with air myelography a vertical radiolucent line can appear, due to air collection (8) in a deep central anterior fissure, simulating a splitting of the cord; even a sufficiently strong cerebrospinal fluid surface tension between the cord elements and the posterior meninges has been described as the cause of a dorsally fixed cord not revealed by surgery. This fixation was diagnosed by air myelagraphy because of lack of mobility of the spinal cord thought to be shown by radiographs taken during movement from the supine to the prone position. From this, it emerges that the differentiation of diasternatomyelia from pseudodiastematomyelia when applying conventional radiological procedures may cause ~roblemsin interpretation. By locating even a minimally calcified septum or intramedullary cleft with the help of the noninvasive CT, the diagnosis of diastematomyelia is appreciably improved. For early recognition of diastematomyelia and subsequent surgical treatment in children suffering from orthopaedic and neurological symptoms of spinal dysraphism and associated grosser anomalies the following radiological procedure should be carried out: 1. Survey radiograph of the spinal column. 2. If a diastematomyelia cannot be diagnosed definitely by I., then CT should be applied before a myelo-
g-aphy. In particular, the medullary conus must be specially studied in order not to overlook a fixation caused by lipoma or a malformation. Linear tomography with its well-known possibilities for false evidence by striped blurring shades, will hardly be necessary for identifying a calcified intraspinal septum. The mechanical obstruction of the medullary ascent by dural or arachnoid adhesion in the region of the septum or conus requires early diagnosis of diasternatomyelia and prompt operative measures in order to avoid progressive orthopaedic damage and neurological deficits caused by a drag on the spinal cord. Because congenital scoliosis frequently coincides with diastematom~elia,this must first be excluded because measures taken to correct the scoliosis may result in neurological damage, such as paresis of the legs (10). In this context it must be emphasized that a diasternatomyelia can remain symptomless. The asymptomatic cases with a low lumbar fixed conus suggest that the fixation of the cord in diasternatomyelia with subsequent development of symptoms may not only be caused by traction or pressure effects on the cord, but also by other factors including abnormal vascularization, i. e. stenosis of the arterial spinal axes. C T of lumbar and dorsal spines revealed no definite macroscopic dysplastic changes of the cord. Where a diastematomyelia shows spinal cord changes demonstrated by CT, a fixation of the cord seems more likely than in the absence of such changes.
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Spinal disorders in computed tomography
Zusammenfassung
Es wurden 9 Patienten (8 Madchen, 1 Junge) mit dysrhaphischen Storungen der Wirbelsaule und rontgenologisch in 6 Fallen nicht eindeutig nachweisbarer Diastematomyelie computertomographisch untersucht. I n 8 Fdlen - ausschliel3lich Madchen - liei3 sich im Computertomogramm 7mal eindeutig ein kalzifiziertes, intras~inalesKnochenseptum und einma1 eine Zweiteilung des Ruckenmarkes ohne erkennbares Septum nachweisen. Bei allen Patienten mit klinischer Symptomatik konnten dysplastische, von der Segmenthohe unabhangige Markveranderungen, wie Kaliberschwankungen und ein heterogenes Absorptionsmuster der Medulla, nachgewiesen werden. Drei Madchen rnit klinisch symptomloser Diastematomyelie zeigten computertomographisch kein auffalliges Absorptionsmuster des Ruckenmarkes. Asymptomatische Diastematomyelien weisen darauf hin, dai3 die gewohnlich begleitenden orthopadischen und ne~rolo~ischen Storungen ursachlich nicht allein auf eine mechanische Behinderung des Ascensus medullae zuriickgefuhrt werden konnen, sondern durch eine komplexe Atiologie einschliei3lich medullarer Vaskularisationsstorungen bedingt sind. Eine durale bzw. subarachnoidale Fixation des Riickenmarkes 1Zi3t sich computertomographisch direkt nicht nachweisen. Nur bei computertomographischen Hinweisen auf einen tiefstehenden Conus medullaris, Markdysplasien, intraspinale Lipome, Zysten
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oder Fisteln ist mit groi3er Wahrscheinlichkeit ein mechanisch behinderter Ascensus medullae mit Zugbeanspruchung der nervalen Strukturen anzunehmen. Die methodisch adaquate Aufgabe der C~m~utertomographie in der Diagnostik der Diastematomyelie und Markdysplasie besteht nach unseren bisherigen Erfahrungen bei Beriicksichtigung der herkommlichen radiologischen Untersuchungsmethoden darin, bei rontgenologischem Verdacht auf eine Diastematomyelie auch ein minimal kalzifiziertes Septum definitiv nachzuweisen, eine medullare Zweiteilung ohne Knochenseptum und begleitende grobere Anomalien auszuschliei3en sowie als nicht invasive Methode zur friihzeitigen diagnostischen Sicherung der Diastematomyelie und zum Ausschlufl differentialdiagnostischen einer Pseudodiastematomyelie beizutragen.
References Di Chiro, G., Axelbaum, S. P., Schellinger, D. et al.: Computerized axial tomography in syringomyelia. N. Engl. J. Med. 292: 13-16 (1975). Weinstein, M. A., Rothner, A. D., Duschesneau, P., Dohn, D. F.: Computed tomography in diastematomyelia. Radiology 117: 609-611 (1975). Herren, R. Y., Eduards, J. E.: Dystomyclia (duplication of the spinal cord). Arch. Path. 30: 1203-1214 (1940). Hilal, S. K., Marton, D., Pollack, E.: Diastematomyelia in Children. Radiology 112: 609-621 (1974). James, C. C. M., Lassman, L. P.: Spinal Dysraphism. New York: Appleton-Century-Crofts 1972. Winter, R. B., Haven, J. J., Moe, J. H. et al.: Diastematomyelia and congenital spine
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9. Rand, R. W., Rand, C. W.: Epidermoids, dermoids and dermal sinuses. Extradural spinal cysts. In: Intraspinal Tumors of Childhood, 348-381 and 425-446, by R. W. and C. W. Rand, ThomasISpringfield, Ill. 10. Vandresse, J. H. and Cornelis, G.: Report of eight Observations. Neuroradiology 10: 87-93 (1975).
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deformities. J. Bone Joint Surgery 56: 2739 (1974). 7. Neuhauser, E. B. D., Wittenborg, M. H., Dehlinger, K.: Diastematomyelia: transfixation of the cord or cauda eauina with congenital anomalies of the spine. Radiology 54: 659-664 (1950). 8. Scatliff, J. H., Till, K., Hoare, R. D.: Incomplete, false and true Diastematomyelia. Radiology 116: 349-354 (1975).
