Computed tomography of the lumbosacral spine:

Transcription

1 THIS ExHIBIT, A 5ELECFION OF THE COMPUTED TOMOGRAPHY AND NEURORADIOLOGY PANELS, WAS DISPLAYED AT THE 67Th SCIENTIFIC ASSEMBLY AND ANNUAL MEETING OF THE RADIOLOGICAL SOCIETY OF NORTH AMERICA, NOVEMBER 15-20, 1981, CHICAGO, ILLINOIS. Computed tomography of the lumbosacral spine: Normal anatomy, anatomic variants and pathologic anatomy Robert H. Dorwart, M.D.* Jack DeGroot, M.D.t Eberhardt K. Sauerland, M.D., Ph.D. Clyde A. Helms, M.D. James B. Vogler, M.D. Here is a meticulously detailed study correlating CTfindings with transaxial cadaver anatomy, and illustrating common variants and pathologic processes affecting the lumbosacral spine. PART I: NORMAL ANATOMY Introduction The first portion of this exhibit presents a correlative study of the normal anatomy of the human lumbosacral spine. Five millimeter axial CT scans of a fresh human cadaver were exposed on a General Electric CT/T 8800TM wide aperture scanner. Exposures were made before and after the injection of the vertebral bodies of L3, L4, L5 and 51 with a mixture of blue latex and AFB, * From the Department of Radiology, Wilford Hall USAF Medical Center, Lackland Texas. t From the Department of Anatomy, University of California, San Francisco, School of Medicine, San Francisco, California. AFB, From the Clinical Investigative Facility, Wilford Hall USAF Medical Center, Lackland Texas. From the Department of Radiology, University of California, San Francisco, School of Medicine, San Francisco, California. II From the Department of Radiology, David Grant USAF Medical Center, Travis AFB, California. Address reprint requests to R. H. Dorwart, M.D., Dept. of Radiology, Wilford Hall USAF Medical Center, Lackland AFB, Texas, Volume 2, Number 4 November 1982 RadioGraphics 459

2 Introduction an iodinated radiographic contrast agent. The technical factors employed were 120 kvp, mas and a 25 cm field of view. The lumbosacral spine of the cadaver was then resected, frozen in dry ice and sectioned transaxially with a fine band saw. Corresponding CT scans and anatomic sections are compared. Also, 1.5 and 5 mm axial scans of the lumbosacral spines of other human cadavers were recorded, and sagittal and coronal computer reformations were generated from these series of contiguous scans using the ARRANGETM program. These reformations are correlated here with photographs of preserved human lumbosacral spines that have been sectioned in the corresponding planes. In the following article, details of skeletal and ligamentous anatomy, the anatomy of lumbar and lumbosacral intervertebral discs and the anatomic relations of the nerves and venous channels of the lumbosacral spine are illustrated. Finally, important features of sacral anatomy are presented. Localization Key f/i Figure 1 Frontal and lateral radiographs of a dried human lumbosacral spine. Lines drawn through these images, correspond to the planes of the transaxial images in Figures 2, 3, 4, 5, 6, and RadioGraphics November 1982 Volume 2, Number 4

3 Dorwart, et at. Level of L Disc Figure 2 Transaxial CT scan at the L3-4 disc level and at the plane of the L3-4 intervertebral foramina. Straight arrow superior articulating process of L4 on the right; curved arrow postenor elements of L3. -jmri SLIJPP1 I LU :i i c52 27 ipr $- : Level of L Facet Joint Figure 3 Transaxial CT scan at the level of the L3-4 facet joint. SP superior articulating process of L4; IP inferior articulating process of L3; LFC ligamentum flavum and facet capsule. The superior articulating process of the more caudal lumbar vertebra is always anterior and lateral to the inferior articulating process of the vertebra above. The ligamentum flavum and facet capsule blend together at facet joints (FJ). I :. Figure 4 Anatomic section at the same level as Figure 3. The correlate of the lucent zone of the facet joints seen on CT scans (Figure 3, FJ) is made up of synovial cavity and articulating cartilage (also see Figure 13). The distance between the cortical surfaces of the superior and inferior articulating processes normally measures 2-4 mm (1). Volume 2, Number 4 November 1982 RadioGraphics 461

4 - CMII Dorwart, et at. Level of L4 Pedictes..-i LEOPHILU S 2 HPF Figure 5 Transaxial CT scan at the level of the top of the L4 pedicles. P = pedicles; LF ligamentum flavum; A aorta (aneurysmal). The ligamentum flavum bridges the interlaminar spaces, originating on the ventral surface of the lamina above, and inserting on the dorsal surface of the lamina below. The bony neural canal (lateral recess) begins at this level (unlabelied arrow). p. Level of L4 Body (Midplane) I I L I i H I L Figure 6 Transaxial CT scan at the level of the midplane of the body of L4. Straight arrow lateral recess for the fourth lumbar nerve on the right; curved arrow lucent channel within the dorsal vertebral body for the basivertebrai vein. Note that in sections that nearly parallel the vertebral body end plates, the spinal canal is solid bone circumferentially at a level midway between the superior and inferior end plates (the basivertebral vein can be used as a reference point). Scans at this level are in the plane of the pars interarticularis (P1). Pars interarticularis defects (spondylolysis) will present as abnormal breaks posterolaterally in the bony spinal canal (see Figures 47, 48, 83, and 84). P1 SI -1880MM LUVM1LU : APR 2 - Figure 7 Transaxial scan at the level of the dorsal aspect of the L5-S1 disc. Scans at this level without gantry angulation result in imaging (from front to back) the inferior end plate of L5 (L5), the dorsal aspect of the L5-S1 disc (arrows), and the thecal sac (TS). p. 462 RadioGraphics November 1982 Volume 2, Number 4

5 Dorwart, et at. Localization Key Figures 8 and 9 Anteroposterior and lateral localization views of the human cadaver with intravertebral needles in place. The injection of an iodinated contrast agent and blue latex into these needles resulted in the filling of the epidural paraspinal venous plexuses because of anastomoses between them and the basivertebral veins (see Figure 10). ANTERIOR PLEXUS Schematic: Midplane Lumbar Vertebra of BASIVERTEBRAL VEIN LUMBAR VEIN Figure 10 Schematic cross section through the midplane of a lumbar vertebral body showing details of the spinal and paraspinal veins. Note the anastomoses between the basivertebral vein and the anterior internal vertebral veins, and between the antenor internal vertebral veins and the ascending lumbar veins via the intervertebral veins. (Compare with Figure 4.) (Drawing by E. K. Sauerland, M.D.) Volume 2, Number 4 November 1982 RadioGraphics 463

6 Level of L4.5 Disc LUPHILU :v-18.emm LEUF HILUS APR -. U r ?AP x MM 1338 (tip 17A , ,-- Figures 1 1 and 12 Uninjected and injected transaxial CT scans at the L4-5 disc level. The intervertebral disc (L4-5), which is composed of nucleus pulposus and annulus fibrosis, is homogeneously more opaque than the thecal sac (TS), which is usually round or slightly oval in cross section. Straight arrows epidural veins; curved arrows ascending lumbar veins. The slight concavity in the dorsal margin of the healthy young adult lumbar disc is probably due to the posterior longitudinal ligament as it courses between the posterior vertebral body surfaces in the median and paramedian zones; the epidural veins may also contribute to this appearance of concavity. Figure 13 Corresponding anatomical cross section of L4-5 disc. -., :t 464 RadioGraphics November 1982 Volume 2, Number 4

7 Dorwart, et al. Level of L5-S1 Disc (Dorsal Aspect) Figures 14 and 15 Uninjected and injected transaxial CT scans at the level of the dorsal aspect of the L5-S1 intervertebral disc (arrows, Figure 14). Transaxial scans without gantry angulation result in imaging (from front to back) the inferior end plate of L5 (L5), the dorsal aspect of the L5-S1 disc, the epidural veins (straight arrows, Figure 15), and the thecal sac (TS). The dorsal margin of the lumbosacral disc in a healthy young adult is linear or minimally convex posteriorly (2). Figure 16 Anatomic cross section corresponding to the plane of Figures 14 and 15. Note that the separation of the Si nerve roots from the thecal sac results in a mouse ears configuration. Volume 2, Number 4 November 1982 RadioGraphics 465

8 Dorwart, et at. Level of L5 (Midplane) Figures 17 and 18 Uninjected and injected transaxial CT scans at the level of the midplane of L5. Note the lucent channel for the basivertebral vein (curved arrow) in the midline of the dorsal aspect of the body of L5 and the soft tissue opacities that represent the anterior internal vertebral veins (straight arrows), and the segmental lumbar veins (LV) in Figure 17. All of these structures are opacified following intravertebral injection (Figure 18). NT = needle track for the injection of contrast material. Y -96.WIM C LEOPH I LUS 27APR x. v-i 5;, 1 :7 5-0MM 1 44 tjp i2ii RadioGraphics November 1982 Volume 2, Number 4

9 Level of L5-S1 Intervertebral Foramina Figures 19 and 20 Uninjected and injected transaxial CT scans at the level of the L5-S1 intervertebral foramina. Anastomoses between the segmental lumbar vein (LV) and the veins draining the soft tissues dorsal to the spine (unlabelled arrow) are visualized, as are the anterior internal vertebral veins. Volume 2, Number 4 November 1982 RadioGraphics 467

10 Level of L2 Body (Midplane) V -73.0MM ,, LEOPHILUS 2? APR Figures 21 and 22 Uninjected and injected transaxial CT scans at the level of the midplane of the body of L2 demonstrating a prominent segmental lumbar vein (straight arrow) on the right. Such prominent anastomoses between the ascending lumbar veins and the inferior vena cava are most frequently seen at the L2 and L3 levels (3). 468 RadioGraphics November 1982 Volume 2, Number 4

11 Dorwart, et at #{149}1 Midsagittal Reformation 5* C I( PUN PIT ID PHT tim FREDERICK ssp 3 8TH 5.0 SCHN DTE 3-1G80 T MM Al DEGREES DEGREES THKNS: 1 PIXELS Figure 23 Midsagittal computer reformation of a series of scans exposed prior to the injection of a contrast medium. Note the lucency in the dorsal aspect of each vertebral body midway between the superior and inferior end plates (straight arrows) that corresponds to the channel for the basivertebral vein. These lucencies should not be mistaken for lytic lesions or fracture lines T I 22 4 * C FREDERICK ): 3 5TH: DATE: 3/16/80 Figure 24 Midsagittal computer reformation of a series of scans following the injection of a contrast medium. The basivertebral veins are now opacified. 1: (1.3,24.1)MM Al: 90.0 DEGREES A2 0.0 DEGREES THKNS: 2 PIXELS Parasagittal Reformation 22 4 * * Figure 25 Right parasagittal computer reformation in the plane of the anterior internal vertebral veins. This demonstrates the 1: longitudinal rid: #{216}#{216}#{216}#{216}#{216}#{216} course of these veins along the dorsal margins r.nm: FREDERICK of the vertebrae and discs (straight arrows). : 3 STH 5.0 DATE: 3/16/ ,,AH - T: (_ )MM : Al: DEGREES A2: 0.0 DEGREES THKNS: 1 PIXELS Volume 2, Number 4 November 1982 RadioGraphics 469

12 Localization Key /1 Figure 26 Anteroposterior and lateral views of the lumbosacral spine with the levels of Figures 27, 28, 29, 30 and 31 indicated. 470 RadioGraphics November 1982 Volume 2, Number 4

13 Course 5th Lumbar Nerves of Figure 27 Figure 28 Figures 27, 28, 29, 30 and 31 This series of scans traces the course of the 5th lumbar nerves from their origins as nerve roots (R5) from the thecal sac (Figures 27 and 28) through the dorsal ganglia (D5) on Figure 29, to their ventral rami (N5) on Figures 30 and 31. Figure 29 Figure 30 ; I1 Figure 31 Figure 32 Anatomic cross section corresponding to the level of Figure 28. Note the symmetrical appearance of the epidural fat surrounding the nerves within the lateral recesses. Volume 2, Number 4 November 1982 RadioGraphics 471

14 Dorwart, et at. Course of 5th Lumbar Nerves Figure 33 Coronal computer reformation demonstrating the course of the 5th lumbar nerves (straight arrows). Figure 34 Corresponding anatomic section demonstrating the left 4th and 5th lumbar nerves. The dorsal ganglia are well visualized. :;J IA i 1 Schematic: Formation of Sciatic and Posterior Cutaneous Nerves :4. *, 5- p_ - \\ Figure 35 Schematic drawing depicting the formation of the sciatic and posterior cutaneous nerves of the thigh from the lumbosacral plexus. Note that in this view (from behind), the ventral rami of the 4th and 5th lumbar nerves unite just cranial to the lateral part of the sacrum on each side to form the lumbosacral trunk. This trunk courses anterior to the lateral part of the sacrum and is joined by fibers from Si at the level of the first anterior sacral foramen to form the sciatic nerve. (Drawing by E. K. Sauerland, M.D.) 472 RadioGraphics November 1982 Volume 2, Number 4

15 Level of L1 Figure 36 Transaxial CT scan of a human cadaver through the level of Li after the intrathecal injection of 95% ethanol. The lower level of the conus medullaris is depicted. Note the radial distribution of the ventral and dorsal lumbar and sacral roots around the conus. <: -90 0MM. MYTH POt 1I JUN -. Figure 37 Normal intrathecal anatomy at a level corresponding to Figure 36, shown on a CT reconstruction (REvIEwIM) of a metrizamide myelogram of a patient being evaluated for lumbar spinal stenosis. Level of L3 Figure 38 A transaxial CT reconstruction (REvIEwTM) myelogram at L3 (same patient as in Figure 37). Note the separation of the nerve roots and their arrangement about the filum terminate internum (straight arrow). Volume 2, Number 4 November 1982 RadioGraphics 473

16 Level of S1 (Superior Aspect) Figures 39 and 40 Uninjected and injected transaxial CT scans through the upper part of Si exposed with the gantry in a vertical position. Because of the normal sacrovertebral angulation, part of the lumbosacral disc (L-S) is seen anteriorly. Note the paired lucent channels for the basivertebral veins (straight arrows) that opacify after the injection of a contrast medium (Figure 40). Epidural fat is abundant.. -.s l-...;r Figure 41 Anatomic section corresponding to the plane of Figures 39 and 40. J RadioGraphics November 1982 Volume 2, Number 4

17 Level of S1-2 Figure 42 Injected transaxial CT scan at the 51-2 level. The 52 nerve roots (R2) as they emerge create a mouse ears configuration of the thecal sac. Epidural fat is abundant. The dorsal ganglia of Si (Di) are prominent. An oblique basivertebral venous channel (BV) coursing to the left Si foramen is opacified. The lucent channel for such a vein might be misinterpreted as a fracture line. The lumbosacral trunk is outlined by fat and is situated anterior to the lateral part of the sacrum (L4 5). The first dorsal sacral foramina (DF) are seen. Figure 43 Anatomic section corresponding to the plane of Figure 42. An Si-2 disc remnant is seen just ventral to the thecal sac and the sacral canal. Volume 2, Number 4 November i982 RadioGraphics 475

18 Level of 1st Anterior Sacral Foramina r i,#{231}- k.,. Figure 44 An injected transaxial CT scan at the level of the first anterior sacral foramina. The Si ventral rami are positioned anteriorly, close to the lumbosacral trunk (curved arrow). Some epidural veins opacified with the contrast agent and air (straight arrows) are seen anterior to the thecal sac within the sacral canal. Figure 45 Anatomic section corresponding to the plane of Figure 44. Note the vestigial 51-2 disc. Fatty marrow within the lateral parts of the sacrum accounts for the lucent appearance seen on CT scan (asterisk, Figure 44). Figure 46 Injected transaxial CT scan at the 52 level. The lumbosacral trunk and fibers from the Si ventral ramus have joined to form the sciatic nerve (SC). Within the sacral canal, the dorsal ganglia of 52 (D2) and 53 nerve roots (R3) and opacified epidural veins (curved arrows) can be seen in abundant epidural fat. 476 RadioGraphics November 1982 Volume 2, Number 4

19 Dorwart, et at. PART II: NORMAL VARIANTS Introduction In this section, examples of normal anatomic variants that may mimic or be misinterpreted as evidence of pathologic processes are presented. All of the CT scans were performed on a GE CT/T 8800 wide aperture scanner, using 120 kvp, 5 mm thick scans and 25 cm field of view. The mas, in most cases, was 506. Unless otherwise indicated, all scans were obtained in the transaxial plane and no intravenous or intrathecal contrast agents were employed. Spondylolysis t,._ #,. \ Figure 47 Spondylolysis (pars interarticularis defects) without spondylolisthesis. At the mid L5 level, irregular curvilinear defects in the pars interarticularis of L5 are seen bilaterally (arrows). I -.5 Figure 48 Oblique plain film of the lumbosacral spine, same case as Figure 47, showing the break in the Scottie dog s neck (arrow). Volume 2, Number 4 November 1982 RadioGraphics 477

20 Dorwart, et at. Conjoined Nerve Roots Figure 49 Figures 49 and 50 Conjoined origin of nerve roots from the thecal sac. Note the asymmetric soft tissue density obliterating epidural fat within the left lateral recess of L5 (Figure 49, arrow). Compare this appearance with Figures 28 and 32. A scan at the level of the L5-Si intervertebral foramina shows that there are two nerve roots that have originated from the thecal sac on the left (Figure 50, L5, Si). Figure RadioGraphics November i982 Volume 2, Number 4

21 Nerve Conjoined Roots p Figure 51 Oblique reformation in the plane of origin of the left L5 and Si nerves from the thecal sac. The plane of reformation is shown on transaxial scans at the level of the lateral recess (left image) and intervertebral foramina (right image) by white dotted lines. -.5,, - _5: 5- Figures 52 and 53 Magnified view of the left oblique reformatted image (Figure 52) shows two nerve roots (L5,S1) origmating from the left L5 lateral recess. On the right (Figure 53), L5 originates from the L5 lateral recess, Si originating separately at a lower level, as demonstrated on the magnified right oblique computer reformation. Routine and CT myelographic confirmations were obtained in this case and are reported elsewhere (4). Volume 2, Number 4 November i982 RadioGraphics 479

22 Spina Occutta Bifida.\ A. S L -I J 4 Figure 54 Spina bifida occulta; hypoplastic left lamina at L5. At the upper L5 level, the thecal sac is distorted, and there is no epidural fat on the left. Figure 55 At the level of the L5-Si intervertebral foramina, the thecal sac is distorted, probably secondary to the hypoplastic lamina on the left. Nonjuncture of the lamina in the midline is consistent with occult spina bifida. (The patient had never had low back surgery.) Figure 56 An anteroposterior radiograph of the lumbosacral spine of the same patient shows the anomalies described in Figure 55. I 480 RadioGraphics November 1982 Volume 2, Number 4

23 Hemisacralization of L5 -F,: 5 S -,*-... :2:;. _5 t T. 5.;, _p#{149} Figure 57 Hemisacralization of L5 on the left. At the level of the L5-Si intervertebral foramina, the transverse process of L5 on the left is markedly enlarged. There is residual Pantopaque#{174} from a previous myelogram within the thecal sac. Figure 58 At the upper Si level, the lateral part of Si on the left is enlarged and sclerotic. The enlarged transverse process of L5 was shown on a contiguous series of CT scans to be fused with the left Si lateral part. This entire structure forms a pseudoarticulation with the ilium. Figure 59 Corresponding anteroposterior radiograph of the lumbosacral spine demonstrating hemisacralization of L5 on the left. Volume 2, Number 4 November i982 RadioGraphics 481

24 Introduction PART III: PATHOLOGY Pertinent examples of pathologic anatomy of the lumbosacral spine as demonstrated by CT, are now presented. A GE CT/T 8800 scanner was again employed, and the technical factors were as described in Part II. Unless indicated, no intrathecal or intravenous contrast agent was employed. The cases presented have been confirmed surgically and/or histologically. Bulging Annutus Fibrosis Figure 60 Figures 60 and 61 Bulging annulus fibrosis at L4-5 and L5-Si, respectively. Note the uniformly symmetrical bulging of the disc beyond the lateral margins of the end plate ( midriff bulge ). The ventral margin of the thecal sac is flattened, and is actually convex posteriorly. The epidural fat anterolateral to the thecal sac is obliterated bilaterally, as is the fat normally interposed between the back of the disc and the cortical margin of the superior articulating process. Figure RadioGraphics November 1982 Volume 2, Number 4

25 ._5 Dorwart, et al. Facet Arthropathy Joint Figure 62 L4-5 facet joint arthropathy. Gas is present within the left L4-5 facet joint (arrow). This is a frequent finding of uncertain pathologic significance (1). S 5.J1 Figure 63 A transaxial CT scan at the same level with window and level adjusted for optimal demonstration of bone detail, shows hypertrophy of the superior articulating process of L5. Volume 2, Number 4 November 1982 RadioCraphics 483

26 Herniated Nucleus Pulposus Figure 64 Herniated nucleus pulposus at L4-5. Note the asymmetrically placed epidural soft tissue mass, obliterating the left anterolateral epidural fat. The thecal sac is correspondingly distorted. This appearance is nonspecific and is consistent with an epidural mass of any origin. Depending on the clinical setting, an epidural mass may be caused by a herniated nucleus pulposus, neoplasm, abscess, or hematoma. Figure 65 Herniated nucleus pulposus at L5-Si on the left. There is a soft tissue mass in the anterolateral epidural fat, obliterating the outline of the left Si nerve. 484 RadioCraphics November i982 Volume 2, Number 4

27 Dorwart, et at. Nucleus Herniated Pulposus Figure 66 Focally dominant protrusion of disc material at L5-Si on the left. This case demonstrates the difficulty occasionally encountered in distinguishing a bulging annulus fibrosis from a herniated nucleus pulposus. The annulus fibrosis does appear to be bulging slightly, but there is a focally dominant bulge into the left anterolateral epidural space (arrow). Note that the left Si nerve is displaced slightly posteriorly. Such an appearance, in the proper clinical setting, may be termed a focal protrusion of disc material. Either a bulging annulus fibrosis or a herniated nucleus pulposus may be found at surgery (5). Figure 67 Central herniated nucleus pulposus at the L5-Si interspace. This epidural mass is so focally dominant in the median and paramedian epidural space that a diagnosis of herniated nucleus pulposus should be favored. Approximately 5-8% of posterior herniated discs do occur in the midline (6). Figure 68 Calcified herniated nucleus pulposus at the L5-Si interspace. There is a focally dominant mass in the right anterolateral epidural space, containing opacities whose CT numbers are typical of calcifications (arrows). The right Si nerve is not seen, the right anterolateral fat is obliterated, and the thecal sac is minimally distorted. Differentiating calcified degenerated disc material from osteophytes (spondylosis) may be difficult (5). Volume 2, Number 4 November 1982 RadioGraphics 485

28 Dorwart, et at. Herniated Nucleus Pulposus _5*e,.. _5.1 - Figures 69 and 70 Herniated nucleus pulposus at the level of L5-Si and conjoined origin of Si and 52. This transaxial CT scan at the L5-Si level shows a large, focally dominant epidural mass in the midline extending to the left (arrow). In Figure 70, this mass is highlighted by using the blink mode of the digital display console as described by Helms et al. Figure 71 In this transaxial CT scan at the Si level, an apparent epidural mass is seen in the lateral recess on the left. This might be misinterpreted as a migrated disc fragment. (Same patient as Figures 69 and 70.) 486 RadioGraphics November i982 Volume 2, Number 4

29 Herniated Nucleus Pulposis j;, -I :* - - Figure 72 This myelogram shows the origins of Si and 52 nerves from the thecal sac on the left to be conjoined (arrows). By carefully examining the contiguous series of transaxial scans, the distinction between the herniated flucleus pulposus and the conjoined origin of the nerve roots was recognized before myelography in this case. Myelography is complementary to CT in such a setting, however, and may be necessary to confirm or negate impressions based on the interpretation of CT scans. (Same patient as Figures 69, 70 and 7i.) _ #{149}5_5 Figure 73 Far lateral herniated nucleus pulposus at the L3-4 interspace. This patient complained of pain in the left leg; a metrizamide myelogram was negative. Subsequently, computed tomography showed this focally dominant soft tissue mass extending from the posterolateral aspect of the L3-4 intervertebral disc. The left L3 ventral ramus is posteriorly displaced (arrow). This sort of pathologic process cannot be adequately evaluated by conventional myelography; it is readily demonstrated by computed tomography, however. 5..;.., Volume 2, Number 4 November 1982 RadioGraphics 487

30 Dorwart, et at. Recurrent Herniated Nucleus Pulposus Figure 74 Figures 74 and 75 Recurrent herniated nucleus pulposus at the L4-5 interspace in a patient with a history of previous disc resection. Scans at the L4-5 disc level and the mid L5 level, respectively, show an epidural mass on the left. The size of this mass and its markedly asymmetric distribution favors the diagnosis of recurrent herniated nucleus pulposus. More important, its CT attenuation values were similar to those of other identifiable L4-5 disc material (arrows, Figure 74). Figure RadioGraphics November i982 Volume 2, Number 4

31 Dorwart, et at. Recurrent Herniated Nucleus Pulposus Figure 76 Postoperative fibrosis in the right L5-S1 intervertebral foramen. The soft tissue density in the right foramen (arrows) is a nonspecific finding; but in a patient with a history of previous disc resection, is consistent with recurrent or residual disc material and fibrosis (4). Figure 77 Recurrent herniated nucleus pulposus at the L5-Si interspace. A transaxial CT scan at the level of the L5-Si intervertebral foramina is shown. The diagnosis of recurrent HNP is supported by the gas (arrow) in the left L5-Si intervertebral foramen-a herniated vacuum disc. Volume 2, Number 4 November 1982 RadioGraphics 489

32 Dorwart, et al. Spinal Stenosis Figure 78 Developmental and degenerative spinal stenosis. At the mid L3 level, the sagittal dimension of the bony canal is decreased. As a result, the thecal sac in cross section appears as a flat oval, its transverse diameter greatly exceeding its anteroposterior diameter. The thecal sac is usually round or only slightly oval, its transverse dimension being only slightly greater than its sagittal dimension. Figure 79 At the L4-5 disc level, there is severe stenosis of the thecal sac caused by bulging of the annulus fibrosis, by facet joint and ligamentum flavum hypertrophy, and by developmentally small dimensions. Figure 80 At the mid L5 level, the spinal canal has a trefoil cross sectional appearance. 490 RadioGraphics November i982 Volume 2, Number 4

33 Spondylotysis with Lateral Recess Stenosis Figure 81 Spondylolysis, without spondylolisthesis, resulting in lateral recess stenosis. A metrizamide myelogram demonstrates non-filling of the right L5 nerve root sheath in this 20 year old man who experienced the abrupt onset of a right L5 radiculopathy after falling down steps. Figure 82 A transaxial CT scan at the level of the L4-5 disc shows a minimal annulus fibrosis bulge. Figure 83 A transaxial CT scan at the level of the L5 lateral recess shows narrowing of the right L5 lateral recess (arrow) caused by developmental stricture and a small bone fragment (an osteophyte was seen at surgery). Volume 2, Number 4 November i982 RadioGraphics 491

34 Spondytolysis with Lateral Recess Stenosis Figure 84 A transaxial CT scan at the level of the superior aspect of the L5-Si facets, shows that the facet joints and pars defects are continuous with one another at an acute angulation. Figure 85 An oblique view from a myelogram of the same patient shows that the break in the Scottie dog s neck (straight arrow) joins the facet joint space (curved arrow). I 492 RadioGraphics November i982 Volume 2, Number 4

35 Dorwart, et at. Metastasis Sacral Figure 86 A transaxial CT scan at the level of Si shows breast carcinoma metastatic to the lateral part of the sacrum on the right. The CT attenuation value of the lesion is greater than that of the corresponding point in the lateral part of the sacrum on the left (straight arrow). This is because the normal fatty marrow, which is often present at these sites (see Figures 39, 40, 4i, 44, and 45), is replaced by metastatic tissue of greater attenuation. Note the entrapment of the right Si dorsal ganglion (Di) and the anterior displacement of the lumbosacral trunk (L4,5) on the right by the tumor mass. Figure 87 Malignant melanoma metastatic to the sacral canal and the lateral part of the sacrum on the right at the level of Si. Again, note the increased attenuation of the lateral part of the sacrum on the abnormal right side (straight arrow) compared to a corresponding point in the normal left side (curved arrow). The epidural fat of the sacral canal is completely replaced by the tumor mass, and normal details of the thecal sac, nerves and epidural veins are obliterated (compare with Figure 46). Volume 2, Number 4 November 1982 RadioCraphics 493

36 Epidural Metastasis 4: ) :4 i 5q, L 1 #{163} Figure 88 Breast carcinoma metastatic to the epidural space of L5 and to the multifidus muscle on the right. At the mid L5 level, there is abnormal soft tissue extending as a continuous mass from the epidural space in the right lateral recess, through the intervertebral foramen and into the paraspinal soft tissues dorsal to the spine. (Case courtesy of Dr. John Mani, Ralph K. Davies Medical Center, San Francisco, California.).k I , I- - 4 ri i LL51 5!_ #{149} Figure 89 At the Si level, note the spread of tumor into the right lateral recess of Si (straight arrow) via the first dorsal sacral foramen on the right. (Same patient as Figure 88.) 494 RadioGraphics November i982 Volume 2, Number 4

37 Dorwart, et at. a Paraspinat Nocardiat Abscess Figure 90 Left paraspinal abscess at L4-5 and acquired degenerative spinal stenosis, 8 years after L4-5 disc resection. At the L4-5 interspace, there is a poorly defined inflammatory mass in the multifidus muscle and in the paraspinal space on the left. 4 Figure 91 This transaxial CT scan represents a slightly lower level (upper part of the body of L5). The window setting and level have been adjusted to record bone detail optimally. Irregular bone destruction and sclerosis and acquired spinal stenosis caused by degenerative hyperostosis are seen. Note the osteophyte projecting into the canal from the right L4-5 facet joint. Figure 92 Paraspinal, bilateral psoas and retroperitoneal abscesses in a 20 year old man with primary dissemmated nocardiosis. (The patient s immune status was normal.) At L2-3, the inflammatory mass involves the retroperitoneum, psoas muscles and the anterior epidural space in continuity (Pantopaque#{174} in the thecal sac is compressed posteriorly). Volume 2, Number 4 November i982 RadioGraphics 495

38 Dorwart, et at. Intradural Ependymoma; Adhesive Arachnoiditis : - 2. I. Figure 93 This transaxial CT scan at the level of L4 shows an intradural ependymoma and adhesive arachnoiditis resulting from subarachnoid hemorrhage. This scan was recorded after a metrizamide myelogram (REvIEw reconstruction), and shows the typical appearance of an intradural neoplasm.,-:.-, r-...5::..1._ ,v +E -: 1 1 I1I-4i - - ; -. :.. :.- Figure 94 This transaxial CT scan at the level of L3 was made after a metrizamide myelogram. Note the abnormal clumping of nerve roots-a finding consistent with arachnoiditis resulting from subarachnoid hemorrhage. (Compare with Figure 38.) 5 TA -5 5 _ -#{149}: : #{149}: C, ri ri ::..,,,. :.-. :, :. : #{149}.L p 4 i #{149}..5., id.:-:_,. #{149}. 496 RadioGraphics November i982 Volume 2, Number 4

39 Subdural Contrast Agent Figures 95 and 96 Anteroposterior and lateral views of a metrizamide myelogram in a patient with sacral metastases from breast carcinoma. Most of the contrast agent has been injected into the subdural space. Figure 97 This transaxial CT scan at the level of L2 was obtained for supplemental evaluation of the conus medullaris after the metrizamide myelogram. Note the distribution of the subdural contrast agent in this scan. Volume 2, Number 4 November 1982 RadioGraphics 497

40 Neurinoma Figure 98 This 38 year old woman had a history of left hip pain of 8 year s duration. An anteroposterior view from a metrizamide myelogram demonstrates right lateral displacement and abnormal tapering of the most caudal portion of the thecal sac, as well as a lytic defect in the upper sacrum. Figure 99 A transaxial, enhanced CT scan at the Si level demonstrates a mass lesion with its epicenter in the sacral canal. A small bud of tissue invades the Si body (arrow) : :k5 Figures 100 and 101 Contiguous scans through the upper sacral canal and the second ventral sacral foramina show that the mass lesion is continuous with that in the upper sacral canal and grows out of the left 52 foramen (arrow, Figure iol). This appearance and clinical history resulted in a specific preoperative CT diagnosis of neurinoma. 498 RadioGraphics November i982 Volume 2, Number 4

41 Lipomeningocele; Tethered Cord Figure 102 Lipomeningocele with tethered cord. A transaxial CT scan through the upper half of L5 demonstrates dysraphism and a meningocele. An intrathecal mass is seen; its CT attenuation values are consistent with fat (arrow). This permits a definitive diagnosis of lipoma. The soft tissue shadow within the lipoma represents the tethered cord. (Case courtesy of Dr. John Mani, Ralph K. Davies Medical Center, San Francisco, California.) 1. Carrera GF, Haughton VM, Syvertson A, Williams AL. Computed tomography of the lumbar facet joints. Radiology 1980; 134: Haughton VM, Syvertson A, Williams AL. Soft-tissue anatomy within the spinal canal as seen on computed tomography. Radiology 1980; 134: Theron J, Monet J. Spinal Phlebography. Springer-Verlag, New York, 1978, pp Helms CA, Dorwart RH, Gray M. The CT appearance of conjoined nerve roots and differentiation from a herniated nucleus pulposus. Radiology 1982; 144: Haughton VM, Eldevik OP. Magnaes B, Amundsen P. A prospective comparison of computed tomography and myelography in the diagnosis of herniated lumbar disks. Radiology 1982; 142: Williams AL, Haughton VM, Syvertson A. Computed tomography in the diagnosis of herniated nucleus pulposus. Radiology 1980; 135: References Volume 2, Number 4 November 1982 RadioGraphics 499