Neuroradiolngv
Neuroradiology 17, 71-75 (1979)
© by Springer-Verlag 1979
Computed Tomography and Spinal Dysraphism: Clinical and Phantom Studies* J. H. Scatliff, W. D. Bidgood, Jr., K. Killebrew and E. V. Staab Department of Radiology, University of North Carolina School of Medicine, Chapel Hill, USA
Summary. Two cases illustrating the value of CT in the assessment of spinal dysraphic tissue are presented. In one case, the configuration and origins of two osseous diastematomyelic spurs were shown well; in the second case, the CT recognition of a sacral lipoma led to air myelographic confirmation of the tumor and tethered cord. CT phantom studies indicated that dysraphic tissues, such as fat, cartilage, and fibrous tissue, are better identified and quantitated in the spinal canal when surrounded by air. Varying degrees of image degradation occur with water (simulating CSF) or metrizamide.
Key words: Computed tomography - Spinal dysraphism - Diastematomyelia - Air myelogram
Computed tomography now appears to be a useful guide for more definitive neuroradiological procedures in the study of spinal dysraphism [1, 6, 8, 9]. The development of short-time (2-4 s) body scanners has promoted better recognition of diastematomyelic tissues, abnormal cord positions, and intracanalicular tumors. The purpose of this report is to present two clinical examples of the utility of CT scanning in the management of spinal dysraphism. In addition, phantom studies are described which evaluate CT clarification of dysraphic tissues when surrounded by water (CSF), gas, and watersoluble myelographic media.
except for diastematomyelia. There was sensory loss on the dorsum of the left foot but no other sensory or motor changes. There was intermittent enuresis, but a cystometrogram was negative. CT scanning (21./2 min Delta scanner) of the lower spine revealed two midline bone spurs, which divided the canal completely at T~2 and L1 (Fig. i b, c). The canal was moderately widened at this level. The cord appeared to extend to the sacral region. No intracanalicular lipomas were seen. Since the neurological findings were minimal and the gait was normal, periodic clinical observation is now being carried out. Case 2. A woman aged 38 complained of increasing pain in the lower back and both legs. There was a probable small midsacral meningocele at birth which ruptured and left a scarred dimple. At age 9, the patient developed an abnormal gait, and asymmetry of the lower extremities, the right leg was smaller than the left. There had been intermittent urinary and fecal incontinence since childhood. Films of the lumbosacral spine revealed cystic expansion of the sacral canal. This was confirmed by CT (Delta 2010), which also disclosed an intracanalicular lipoma within the cystic area (Fig. 2 a). The lipoma and posterior displacement with tethering of a low cord were brought out by air myelography (Fig. 2b). Partial resection of the lipoma and lysis of congenital cord adhesions was carried out, after which the pain in the back and legs decreased but the urinary retention with incontinence continued.
Case Reports Case 1. The IVP (Fig. i a) of a girl aged ten, who was being treated for juvenile diabetes mellitus and recurrent upper urinary tract infection, was negative * This work was presented at the XI. Symposium Neuroradiologicum in Wiesbaden, June 1978.
Phantom Studies A phantom was prepared to study the capabilities of CT for resolution of dysraphic tissues. The experimental conditions closely duplicated several potential clinical situations. 0028-3940/79/0017/0071/$01. O0
72
J.H. Scatliff et al.: CT and Spinal Dysraphism
Fig. l a , b and c. a Arrows denote diastematomyelic spurs at T12 and L 1 in an IVP. b Spur at T12 (arrow) arises from posterior elements. e Spur at L1 (arrow)has base on vertebral body. Hemicords (open arrows) are well seen. Minimal spina bifida is also present
Fig.2a and b. CT of sacrum shows expanded canal. Lucency (arrows) is lipoma which was confirmed by CT numbers, b Air myelogram shows lipoma (lower arrow) tethered by anomalous cord (upper arrow)
J. H. Scatliff et al.: CI" and Spinal Dysraphism
73
Fig. 3a, b, e and d. Photomicrograph of chicken breast bone. One septum is bone (arrow). Remaining septa are mixtures of bone, cartilage and fibrous tissue. Lower septum was broken in slide preparation, b Chicken bone has been placed in balloon filled with air, in spinal canal of test vertebra. Air is present in decayed portions of vertebra. Right arrow denotes higher density bone septum. Left arrow shows intermediate density of osseous-cartilagenous septum. L o w e r arrow points to fibrocartilagenous septum of low density. Minimal distortion (narrowed) of septa is present. White dot is a cursor, e Chicken bone has been placed in water to simulate CSF. Bony septum and osseous portion of septum on left have the same density. The thinner fibrocartilagenous septum is of increased density. Septa are less distinct and appear larger. d Chicken bone is in metrizamide (190 mg/ml). Septal densities are similar. Septa are enlarged and distorted. Positioning of dysraphic tissues in vertebral body slightly different in a, b, c
H u m a n t h o r a c i c v e r t e b r a e i m m e r s e d in w a t e r s o a k e d t o w e l s s e r v e d as t h e p r i n c i p a l unit in t h e p h a n t o m . C h i c k e n o r r a t tissues, i n c l u d i n g b o n e , fibr o c a r t i l a g e , o r fat, w e r e p l a c e d in a small, o b l o n g b a l l o o n w h i c h was t h e n s u s p e n d e d in t h e v e r t e b r a l canal. C T a s s e s s m e n t of t h e s e tissues w h e n i n v e s t e d b y air, w a t e r , o r m e t r i z a m i d e ( 1 9 0 m g / m l ) was c a r r i e d out. T h e C T factors, i n c l u d i n g w i n d o w settings a n d c e n t e r s , w e r e m a i n t a i n e d as closely as p o s s i b l e for all c o m p a r i s o n s . Slice t h i c k n e s s was 1 cm, using the Delta 2010 machine. T h e i m a g e s o b t a i n e d i n d i c a t e t h a t air s u r r o u n d i n g s i m u l a t e d d y s r a p h i c tissues p r o d u c e s b e t t e r identific a t i o n of tissue c o m p o n e n t s as w e l l as m o r e e x a c t r e n d i t i o n of t h e d i m e n s i o n s of t h e i n t r a c a n a l i c u l a r material. F i g u r e 3 i l l u s t r a t e s v a r i a t i o n of tissue r e c o g n i t i o n as w e l l as d i s t o r t i o n of tissue size w h e n d i f f e r e n t spinal c a n a l m e d i a w e r e used. T h e b r e a s t b o n e of a
74
J. H. Scatliffet al.: CI"and SpinalDysraphism well determined in water (Fig. 4b). Small soft tissue elements could also be seen with air in the canal but were obscured by water and metrizamide. The nature of the soft tissues appears to be better defined with air. Figure 4 a shows that the fat particle studied in Figure 4 b also has connective tissue. These density differences could not be resolved with adjacent water or metrizamide. The phantom studies also indicated the need for optimum computer settings. It was found that low center settings with constant windows enlarged intracanalicular phantoms 1.3 to 1.5 times. Variation of window settings with constant centers did not lead to similar distortion. If extremes of window settings were used, significant distortion occurred.
Discussion
Fig. 4a and b. a Fat segment in balloon has been surrounded by
air. Cursor shows connectivetissue in fat. Margins of fat are well defined with air. b The same fat segment (cursor over fat) surrounded by water is less well defined chicken, with three septa, (Fig. 3 a) proved to be a good test object. One septun was bone, the other two were fibrocartilagenous. When air outlined this structure, CT numbers were sufficiently different to distinguish bone and fibrocartilage (Fig. 3b). When water or metrizamide were used as contrast media, the CT numbers changed, and fibrocartilage could not be differentiated from bone (Fig. 3c, d). The margins of the breast bone were also reduced in sharpness, and the object was distorted and enlarged, especially when metrizamide was used. Air around the intracanalicular phantoms defined the margins of soft tissues to good advantage. The edges of the piece of fat in Figure 4 a are well shown in air. The exact cross-sectional size of the fat is less
The goal of radiological examination of spinal dysraphism is to define lesions that may be dealt with surgically. The majority of neurosurgical opinion holds that release of a spinal cord tethered by lipomas, dural bands, or diastematomyelic spurs may arrest crippling motor or neurological abnormalities. The radiological examinations now performed include plain films, air myelography with tomograms, or oil myelography. Most recently, water-soluble contrast agents have been used, and these can reveal a low tethered cord [3]. The use of CT to study spinal dysraphism adds a new anatomical plane of information. Transverse CT imaging, as shown in our cases, can demonstrate important spinal canal abnormalities. The information gained can then be used to obtain maximum information from noxious radiological procedures. The latter, on the other hand, may be put aside if large, non-resectable intraspinal defects are found by CT. The phantom studies are interesting from several standpoints. The results, although preliminary, indicate that dysraphic tissues commonly seen (bone, fibrocartilage, fat) can be discerned with CT. This has been noted by others [8, 9] in patients. The phantom studies show, however, that CT recognition of different intracanalicular tissues is decreased by surrounding water or water-soluble contrast material while air maintains good definition. The wider range of CT numbers between air and tissues of fat and water density or bone apparently promotes this effect. It also appears that some distortion and magnification, particularly of bone, occurs when CT is used, and CSF (water) or water-soluble agents encompass the material being scanned. Magnification or minification also can be caused by corn-
J. H. Scatliffet al.: CT and Spinal Dysraphism puter settings, and this factor must be kept in mind when analyzing intracanalicular lesions. It appears, and as observed by others [5], that low-center settings cause the greatest degree of bone magnification. O u r work with p h a n t o m s would suggest that C T evaluation of the dysraphic spine m a y be a valuable step at the time of air myelography. Cord tethering in the lumbar or sacral region, when indicated by air myelography, could be confirmed with CT. With sufficient intraspinal air or oxygen, the patient could be transported in the p r o n e position to the CT room. Evaluation in this and the supine and decubitus positions could bring out cord fixation with certainty. In addition, the true nature of tissue tethering or splitting the cord would appear to be resolved m o r e clearly with air and CT. It is h o p e d that this combination of studies m a y p r o v e sufficient for planning the treatment of spinal dysraphism. The possibility of arachnoiditis caused by water-soluble myelographic agents, although seemingly r e m o t e [2, 4, 7], could be set aside.
75 2. Hansen, E.B., Fahrenkrug, A., Praestholm, J.: The late meningeal effects of myelographic contrast media with special reference to metrizamide. Br. J. Radiol. 51, 321-327 (1978) 3. Harwood-Nash, D. C., Fitz, C. R., Resjo, M., Chuang, S.: Congenital and cord lesions in children and computed tomographic metrizamide myelography. Neuroradiology 16, 69-70 (1978) 4. Haughton, V.M., Ho, K. C., Larson, S. J., Unger, G.F., Correa-Paz, F.: Comparison of arachnoiditis produced by megIumine iocarmate and metrizamide myelography in an animal model. Am. J. Roentgenol. 131, 129-132 (1978) 5. Koehler, P. R., Anderson, R. E., Baxter, B., Sorenson, J.: The effect of computed tomography viewer controls on anatomical measurements. Presented at 26th Annual Meeting, Association of University Radiologists, San Antonio, Texas, May 1978 6. Lee, B. C. P., Kazam, E., Newman, A. D.: Computed tomography of the spine and spinal cord. Radiology 128, 95-102 (1978) 7. Skalpe, I. O.: Adhesive arachnoiditis following lumbar myelography with water-soluble contrast agents: A clinical report with special reference to metrizamide. Radiology 121, 647-652 (1976) 8. Weinstein, M.A., Rothner, A.D., Duchesneau, P., Dohn, D. F.: Computed tomography in diastematomyelia. Radiology 117, 609-611 (1975) 9. Wolpert, S. M., Scott, R. M., Carter, B. L.: Computed tomography in spinal dysraphism. Surg. Neurol. 8, 199-206 (1977) Received. 2 August 1978
References 1. Hammerschlag, B. S, Wolpert, S. M., Carter, B. L.: Computed tomography of the spinal canal. Radiology 121, 361-367 (1976)
Dr. J. H. Scatliff Department of Radiology U. N. C. School of Medicine Chapel Hill, NC 27514, USA
Note added in proof: Further p h a n t o m work indicates that the image of small intraspinal tissue elements undergoes greater degradation due to partial volume averaging with water (CSF) or metrizamide and less so with air.
Neuroradiology 17, 71-75 (1979)
© by Springer-Verlag 1979
Computed Tomography and Spinal Dysraphism: Clinical and Phantom Studies* J. H. Scatliff, W. D. Bidgood, Jr., K. Killebrew and E. V. Staab Department of Radiology, University of North Carolina School of Medicine, Chapel Hill, USA
Summary. Two cases illustrating the value of CT in the assessment of spinal dysraphic tissue are presented. In one case, the configuration and origins of two osseous diastematomyelic spurs were shown well; in the second case, the CT recognition of a sacral lipoma led to air myelographic confirmation of the tumor and tethered cord. CT phantom studies indicated that dysraphic tissues, such as fat, cartilage, and fibrous tissue, are better identified and quantitated in the spinal canal when surrounded by air. Varying degrees of image degradation occur with water (simulating CSF) or metrizamide.
Key words: Computed tomography - Spinal dysraphism - Diastematomyelia - Air myelogram
Computed tomography now appears to be a useful guide for more definitive neuroradiological procedures in the study of spinal dysraphism [1, 6, 8, 9]. The development of short-time (2-4 s) body scanners has promoted better recognition of diastematomyelic tissues, abnormal cord positions, and intracanalicular tumors. The purpose of this report is to present two clinical examples of the utility of CT scanning in the management of spinal dysraphism. In addition, phantom studies are described which evaluate CT clarification of dysraphic tissues when surrounded by water (CSF), gas, and watersoluble myelographic media.
except for diastematomyelia. There was sensory loss on the dorsum of the left foot but no other sensory or motor changes. There was intermittent enuresis, but a cystometrogram was negative. CT scanning (21./2 min Delta scanner) of the lower spine revealed two midline bone spurs, which divided the canal completely at T~2 and L1 (Fig. i b, c). The canal was moderately widened at this level. The cord appeared to extend to the sacral region. No intracanalicular lipomas were seen. Since the neurological findings were minimal and the gait was normal, periodic clinical observation is now being carried out. Case 2. A woman aged 38 complained of increasing pain in the lower back and both legs. There was a probable small midsacral meningocele at birth which ruptured and left a scarred dimple. At age 9, the patient developed an abnormal gait, and asymmetry of the lower extremities, the right leg was smaller than the left. There had been intermittent urinary and fecal incontinence since childhood. Films of the lumbosacral spine revealed cystic expansion of the sacral canal. This was confirmed by CT (Delta 2010), which also disclosed an intracanalicular lipoma within the cystic area (Fig. 2 a). The lipoma and posterior displacement with tethering of a low cord were brought out by air myelography (Fig. 2b). Partial resection of the lipoma and lysis of congenital cord adhesions was carried out, after which the pain in the back and legs decreased but the urinary retention with incontinence continued.
Case Reports Case 1. The IVP (Fig. i a) of a girl aged ten, who was being treated for juvenile diabetes mellitus and recurrent upper urinary tract infection, was negative * This work was presented at the XI. Symposium Neuroradiologicum in Wiesbaden, June 1978.
Phantom Studies A phantom was prepared to study the capabilities of CT for resolution of dysraphic tissues. The experimental conditions closely duplicated several potential clinical situations. 0028-3940/79/0017/0071/$01. O0
72
J.H. Scatliff et al.: CT and Spinal Dysraphism
Fig. l a , b and c. a Arrows denote diastematomyelic spurs at T12 and L 1 in an IVP. b Spur at T12 (arrow) arises from posterior elements. e Spur at L1 (arrow)has base on vertebral body. Hemicords (open arrows) are well seen. Minimal spina bifida is also present
Fig.2a and b. CT of sacrum shows expanded canal. Lucency (arrows) is lipoma which was confirmed by CT numbers, b Air myelogram shows lipoma (lower arrow) tethered by anomalous cord (upper arrow)
J. H. Scatliff et al.: CI" and Spinal Dysraphism
73
Fig. 3a, b, e and d. Photomicrograph of chicken breast bone. One septum is bone (arrow). Remaining septa are mixtures of bone, cartilage and fibrous tissue. Lower septum was broken in slide preparation, b Chicken bone has been placed in balloon filled with air, in spinal canal of test vertebra. Air is present in decayed portions of vertebra. Right arrow denotes higher density bone septum. Left arrow shows intermediate density of osseous-cartilagenous septum. L o w e r arrow points to fibrocartilagenous septum of low density. Minimal distortion (narrowed) of septa is present. White dot is a cursor, e Chicken bone has been placed in water to simulate CSF. Bony septum and osseous portion of septum on left have the same density. The thinner fibrocartilagenous septum is of increased density. Septa are less distinct and appear larger. d Chicken bone is in metrizamide (190 mg/ml). Septal densities are similar. Septa are enlarged and distorted. Positioning of dysraphic tissues in vertebral body slightly different in a, b, c
H u m a n t h o r a c i c v e r t e b r a e i m m e r s e d in w a t e r s o a k e d t o w e l s s e r v e d as t h e p r i n c i p a l unit in t h e p h a n t o m . C h i c k e n o r r a t tissues, i n c l u d i n g b o n e , fibr o c a r t i l a g e , o r fat, w e r e p l a c e d in a small, o b l o n g b a l l o o n w h i c h was t h e n s u s p e n d e d in t h e v e r t e b r a l canal. C T a s s e s s m e n t of t h e s e tissues w h e n i n v e s t e d b y air, w a t e r , o r m e t r i z a m i d e ( 1 9 0 m g / m l ) was c a r r i e d out. T h e C T factors, i n c l u d i n g w i n d o w settings a n d c e n t e r s , w e r e m a i n t a i n e d as closely as p o s s i b l e for all c o m p a r i s o n s . Slice t h i c k n e s s was 1 cm, using the Delta 2010 machine. T h e i m a g e s o b t a i n e d i n d i c a t e t h a t air s u r r o u n d i n g s i m u l a t e d d y s r a p h i c tissues p r o d u c e s b e t t e r identific a t i o n of tissue c o m p o n e n t s as w e l l as m o r e e x a c t r e n d i t i o n of t h e d i m e n s i o n s of t h e i n t r a c a n a l i c u l a r material. F i g u r e 3 i l l u s t r a t e s v a r i a t i o n of tissue r e c o g n i t i o n as w e l l as d i s t o r t i o n of tissue size w h e n d i f f e r e n t spinal c a n a l m e d i a w e r e used. T h e b r e a s t b o n e of a
74
J. H. Scatliffet al.: CI"and SpinalDysraphism well determined in water (Fig. 4b). Small soft tissue elements could also be seen with air in the canal but were obscured by water and metrizamide. The nature of the soft tissues appears to be better defined with air. Figure 4 a shows that the fat particle studied in Figure 4 b also has connective tissue. These density differences could not be resolved with adjacent water or metrizamide. The phantom studies also indicated the need for optimum computer settings. It was found that low center settings with constant windows enlarged intracanalicular phantoms 1.3 to 1.5 times. Variation of window settings with constant centers did not lead to similar distortion. If extremes of window settings were used, significant distortion occurred.
Discussion
Fig. 4a and b. a Fat segment in balloon has been surrounded by
air. Cursor shows connectivetissue in fat. Margins of fat are well defined with air. b The same fat segment (cursor over fat) surrounded by water is less well defined chicken, with three septa, (Fig. 3 a) proved to be a good test object. One septun was bone, the other two were fibrocartilagenous. When air outlined this structure, CT numbers were sufficiently different to distinguish bone and fibrocartilage (Fig. 3b). When water or metrizamide were used as contrast media, the CT numbers changed, and fibrocartilage could not be differentiated from bone (Fig. 3c, d). The margins of the breast bone were also reduced in sharpness, and the object was distorted and enlarged, especially when metrizamide was used. Air around the intracanalicular phantoms defined the margins of soft tissues to good advantage. The edges of the piece of fat in Figure 4 a are well shown in air. The exact cross-sectional size of the fat is less
The goal of radiological examination of spinal dysraphism is to define lesions that may be dealt with surgically. The majority of neurosurgical opinion holds that release of a spinal cord tethered by lipomas, dural bands, or diastematomyelic spurs may arrest crippling motor or neurological abnormalities. The radiological examinations now performed include plain films, air myelography with tomograms, or oil myelography. Most recently, water-soluble contrast agents have been used, and these can reveal a low tethered cord [3]. The use of CT to study spinal dysraphism adds a new anatomical plane of information. Transverse CT imaging, as shown in our cases, can demonstrate important spinal canal abnormalities. The information gained can then be used to obtain maximum information from noxious radiological procedures. The latter, on the other hand, may be put aside if large, non-resectable intraspinal defects are found by CT. The phantom studies are interesting from several standpoints. The results, although preliminary, indicate that dysraphic tissues commonly seen (bone, fibrocartilage, fat) can be discerned with CT. This has been noted by others [8, 9] in patients. The phantom studies show, however, that CT recognition of different intracanalicular tissues is decreased by surrounding water or water-soluble contrast material while air maintains good definition. The wider range of CT numbers between air and tissues of fat and water density or bone apparently promotes this effect. It also appears that some distortion and magnification, particularly of bone, occurs when CT is used, and CSF (water) or water-soluble agents encompass the material being scanned. Magnification or minification also can be caused by corn-
J. H. Scatliffet al.: CT and Spinal Dysraphism puter settings, and this factor must be kept in mind when analyzing intracanalicular lesions. It appears, and as observed by others [5], that low-center settings cause the greatest degree of bone magnification. O u r work with p h a n t o m s would suggest that C T evaluation of the dysraphic spine m a y be a valuable step at the time of air myelography. Cord tethering in the lumbar or sacral region, when indicated by air myelography, could be confirmed with CT. With sufficient intraspinal air or oxygen, the patient could be transported in the p r o n e position to the CT room. Evaluation in this and the supine and decubitus positions could bring out cord fixation with certainty. In addition, the true nature of tissue tethering or splitting the cord would appear to be resolved m o r e clearly with air and CT. It is h o p e d that this combination of studies m a y p r o v e sufficient for planning the treatment of spinal dysraphism. The possibility of arachnoiditis caused by water-soluble myelographic agents, although seemingly r e m o t e [2, 4, 7], could be set aside.
75 2. Hansen, E.B., Fahrenkrug, A., Praestholm, J.: The late meningeal effects of myelographic contrast media with special reference to metrizamide. Br. J. Radiol. 51, 321-327 (1978) 3. Harwood-Nash, D. C., Fitz, C. R., Resjo, M., Chuang, S.: Congenital and cord lesions in children and computed tomographic metrizamide myelography. Neuroradiology 16, 69-70 (1978) 4. Haughton, V.M., Ho, K. C., Larson, S. J., Unger, G.F., Correa-Paz, F.: Comparison of arachnoiditis produced by megIumine iocarmate and metrizamide myelography in an animal model. Am. J. Roentgenol. 131, 129-132 (1978) 5. Koehler, P. R., Anderson, R. E., Baxter, B., Sorenson, J.: The effect of computed tomography viewer controls on anatomical measurements. Presented at 26th Annual Meeting, Association of University Radiologists, San Antonio, Texas, May 1978 6. Lee, B. C. P., Kazam, E., Newman, A. D.: Computed tomography of the spine and spinal cord. Radiology 128, 95-102 (1978) 7. Skalpe, I. O.: Adhesive arachnoiditis following lumbar myelography with water-soluble contrast agents: A clinical report with special reference to metrizamide. Radiology 121, 647-652 (1976) 8. Weinstein, M.A., Rothner, A.D., Duchesneau, P., Dohn, D. F.: Computed tomography in diastematomyelia. Radiology 117, 609-611 (1975) 9. Wolpert, S. M., Scott, R. M., Carter, B. L.: Computed tomography in spinal dysraphism. Surg. Neurol. 8, 199-206 (1977) Received. 2 August 1978
References 1. Hammerschlag, B. S, Wolpert, S. M., Carter, B. L.: Computed tomography of the spinal canal. Radiology 121, 361-367 (1976)
Dr. J. H. Scatliff Department of Radiology U. N. C. School of Medicine Chapel Hill, NC 27514, USA
Note added in proof: Further p h a n t o m work indicates that the image of small intraspinal tissue elements undergoes greater degradation due to partial volume averaging with water (CSF) or metrizamide and less so with air.
