Intradural lipomas of the spinal cord A clinicopathological correlation BRUCE J. AMMERMAN,M.D., JAMES M. HENRY, M.D., LTC, MC, USA, UMBEI~TO DE GIROLAMI, M.D., MA~Oa, MC, USA, AND KENNETH M. EARLE, M.D.
Department of Neurological Surgery, The George Washington University Medical Center, Washington, D.C., and the Neuropathology Branch, Armed Forces Institute of Pathology, Washington, D.C. ~" Nine original cases of intradural spinal cord lipomas have been examined from a clinical and pathological standpoint. These tumors occur more commonly in men in the second to fourth decade and are found most frequently in the thoracic spinal cord. Paraparesis, sensory changes, urinary incontinence, and pain are frequent presenting complaints. Myelography is the diagnostic study of choice. All lipomas in this series were located primarily within the cord; four of these also presented an extramedullary extension. Admixed nerve bundles were present in five cases with associated hypertrophic onion-bulb formations in three. Decompression with biopsy or subtotal resection is the operative procedure of choice. KEY WORDS 9 lipoma 9 spinal cord neoplasm 9 intradural lipoma 9 onion-bulb formation 9 hamartoma
I
NTRADURAL spinal cord lipomas are encountered infrequently by the clinician or pathologist, since they occur in less than 1% of all spinal cord tumors? Although several authors have described their clinical experience with such lesions, complete clinicopathological correlation is available for only a small number of cases. 1'2,4'6 8 This paper presents the clinical and morphological findings based on a review of nine original cases of intradural spinal lipomas, and represents one of the largest available series of completely documented cases.
J. Neurosurg. / Volume44 / March, 1976
S u m m a r y of Cases
Clinical Material Nine cases of intradural spinal cord lipomas were reviewed including seven patients from the files of the Armed Forces Institute of Pathology and two from The George Washington University Medical Center. Only cases with verified intradural lesions were selected. Hematoxylin and eosin stains were employed routinely for microscopic evaluation in each case. One case 331
B. J. Ammerman, et al. TABLE 1 Presenting signs and symptoms in nine patients
Signs and Symptoms
No. of Cases
paraparesis long tract signs sensory changes urinary incontinence pain unilateral extremityweakness impotence
6 4 4 3 3 2 1
bral bodies, or pedicular destruction. No associated developmental defects in the vertebrae were noted. Myelography, performed in seven cases, revealed a complete block to the flow of contrast media in two and defects in the remaining five patients. Cerebrospinal fluid protein levels were recorded in four cases and were uniformly elevated, ranging from 72 to 1660 mg%. Tumor location ranged from T-I to L-I (Table 2); there were no cervical lesions in this series. The most frequent area of involvement was the upper thoracic cord, although the tumor often extended for several segments within the cord. The tumor was located exclusively within the cord in five instances, while four cases were associated with an extramedullary component. The surgical procedures consisted of decompressive laminectomy with biopsy and/or subtotal resection in five patients, and decompressive laminectomy with total excision in two. Operative reports were not available in two cases. The postoperative status of the patient appeared to be related to the extent of surgical removal. Both patients with total excision were paraplegic post-operatively, whereas all patients with sub-total resection or biopsy showed either improvement or minimal deterioration of preoperative status. All patients were followed for at least I year and none demonstrated a recurrence within this time.
(Case 6) was also studied with electron microscopy. Seven of these nine cases of intradural spinal lipomas occurred in males. The average age at time of diagnosis was 37 years, with a range of 2 to 73 years; seven of the patients were first seen between 25 and 50 years of age. Most patients had been symptomatic for about 2 years before seeking medical attention. There was no suggestion of a familial incidence in any of these cases. Presenting signs and symptoms are given in Table 1. Paraparesis ranged from mild to moderate, although no patient was paraplegic at the time of initial examination. Sensory disturbances included sensory levels to pinprick, diminished position and vibratory appreciation, and paresthesias. Urinary incontinence was intermittent and no patient had loss of bowel control. Pain, when present, was generally localized to the involved area of the thoracic or the thoracolumbar spine and Representative Case Reports was not radicular in nature. Two patients treated with differing degrees Complete spine x-ray films were available of surgical extirpation are described. Case 9 in three cases. None revealed changes emphasizes the favorable result which may be associated with mass lesions, such as widen- obtained by decompression and conservative ing of the spinal canal, scalloping of the verte- removal of intradural lipomas of the spinal cord; Case 5 illustrates the severe morbidity associated with a more radical procedure. TABLE 2 Case 9. This 46-year-old woman presented with back pain, occasional numbness of the Level and location of lipomas in nine patients right thigh, and intermittent urinary inconCase tinence for a period of several years. Physical No. Level Location examination revealed no sensory, motor, or intramedullary 1 T2-5 reflex abnormalities. Cystometrogram find2 T3--4 intramedullaryand extramedullary ings were consistent with a neurogenic 3 T-12 intramedullaryand extramedullary bladder. At myelography a defect was noted 4 T-3-L-1 intramedullary at T-11 and, at surgical exploration, a tumor 5 T6-8 intrameduUary extending from T-10 to T-12 was seen. The 6 T4-6 intramedullary 7 T-1 intramedullaryand extramedullary lipoma was located within the cord while an intramedullary 8 T-4 extramedullary extension was noted pos9 T10-12 intramedullaryand extramedullary teriorly. The tumor was subtotally excised as 332
J. Neurosurg. / Volume 44 / March, 1976
I n t r a d u r a l lipornas of t h e spinal c o r d it merged imperceptibly with the spinal cord parenchyma. Postoperatively the patient had no additional neurological deficit. Case 5. This 37-year-old man presented with a 3-year history of impotence and 2 years of progressive paraparesis with numbness of the right leg. A sensory level was noted at T-8 and bilateral Babinski signs were present. Myelography revealed an intramedullary lesion that extended from T-6 to T8. Surgery confirmed the intramedullary location of the tumor and a total excision was performed. Postoperatively the patient was paraplegic and incontinent.
Morphology Gross Appearance. A composite description of gross features made at the time of surgery or pathological examination follows. Lipomas of the spinal cord chaacteristically present as soft, yellow, fusiform tumors which occupy a portion of the spinal cord parenchyma. The intraparenchymal margins are frequently indistinct, and adjacent nerve roots may also be incorporated into the lesion, which may extend for several segments within the cord. Although the pertinent literature indicates that all portions of the cord may be involved, the lesions described in this series were located predominantly in the thoracic cord. Microscopic Examination. Nine specimens of variable size were available for histological examination; one specimen (from Case 6) was also examined with the electron microscope to evaluate the relationship of the lipoma to admixed nerve bundles and related hypertrophic onion-bulb formations. The major portion of each biopsy specimen was composed of large, regular, polygonal, reticulated, optically-empty spaces with delicate cytoplasmic membranes and unremarkable, eccentric nuclei consistent with mature fat. There was no microscopic evidence of immature or poorly-differentiated fat cells, pleomorphism, mitotic activity, or parenchymal invasion, and the histological impression was that of an inert, benign neoplasm or hamartoma (Fig. 1). Five cases contained admixed nerve bundles of variable size which were located predominantly at the periphery of the lesion and which were consistent with entrapped spinal nerve roots (Fig. 2). The nerve bundles in two cases were associated with prominent spindle cells which J. Neurosurg. / Volume44 / March, 1976
FIG. 1. Photomicrograph showing mature fat and entrapped nerve bundles. H & E, X 22. were morphologically consistent with Schwann cells. In three cases, the spindle cells were arranged around the axons in concentric lameUae that resulted in the formation of typical onion-bulb structures (Fig. 3), which have been described as a nonspecific feature associated with a variety of chronic, hypertrophic neuropathies? Eight of the cases contained remnants of a thin but distinct fibrous capsule at the margin of the biopsy, and an equal number contained various degrees of admixed collagen. Two cases showed small microfoci of calcification. Small aggregates of lipid-laden macrophages were occasionally seen in the periphery of the lesions. Vascularity was not abundant in these specimens, and was proportional to the amount of supporting stroma within the
FtG. 2. Photomicrograph showing full section of lesion containing collagen, mature fat, and entrapped, hypertrophic nerve bundles (arrow). H&E, X8. 333
B. J. Ammerman, et al. TABLE 3 Morphological features in nhle cases of intradural lipomas of the spinal cord
Case No.
Fat
Nerve Bundles
Onion Bulbs
1 2 3 4 5 6 7 8 9
mature mature mature mature mature mature mature mature mature
prominent moderate minimal none minimal prominent none none none
prominent none none none minimal prominent none none none
SpindleCells Capsule Collagen Calcification Lipid-laden (SchwannCells) Macrophages prominent minimal none none moderate prominent none none none
lesions. There was no pattern of angiolipoma among these cases (Table 3). Ultrastructure
Formalin-fixed tumor tissue was minced, osmicated, dehydrated in a series of graded alcohols, and embedded in Epon 812. Thick sections of 1 # were stained with toluidine blue and examined with the light microscope. The tissue consisted mostly of fat cells in which lay stellate-shaped aggregates of spindle-shaped cells. In one instance these
present present present present present present present none present
prominent none minimal minimal prominent moderate moderate moderate prominent
none none none none none microfoci none none microfoci
none none none present none none none none none
cells appeared to form a whorl around a round, finely-stippled structure that measured approximately 8 # in diameter. Selected blocks were trimmed, thin sections were cut in the silver range with the LKB ultramicrotome, stained with uranyl acetate and lead citrate, and examined with the Siemens and Hitachi electron microscopes. Tissue preservation was quite poor as evidenced by rupture of plasma membranes, disintegration of cytoplasmic organdies, and wide separation of cells by spaces filled with granular and filamentous electron-dense material. Two general categories of cells could be identified. The predominant cell type was characterized by abundant intracytoplasmic round bodies which contained osmiophilic granular material with variable packing density. A second cell was found admixed which had an elongated nucleus, scanty cytoplasm, no evidence of the intracytoplasmic bodies described above, and a prominent basement membrane (Fig. 4). The ultrastructure of this cell is consistent with that of a Schwann cell.
Discussion
FIG. 3. Photomicrograph of hypertrophic onionbulb formations. H & E, • 180. 33,t
Nine original cases of intradural spinal cord lipomas have been presented with clinicopathological correlation. This lesion occurs more c o m m o n l y in men, as characterized by the 3:1 ratio in this series; other authors have noted a similar preponderance. 8'8 Most patients in this series were symptomatic for about 2 years prior to diagnosis and presented during the second, third, and fourth decades of life. Presenting complaints included paraparesis, sensory disturbances, urinary incontinence, and pain. Myelography is the diagnostic study of J. Neurosurg. / Volume 44 / March, 1976
Intradural lipomas of the spinal cord
FIG. 4. Electron micrograph of Schwann cell in hypertrophic onion-bulb formations illustrating basement membrane (arrows). Uranyl acetate and lead citrate, • 48,600.
choice for localization of this lesion. Cerebrospinal fluid protein was consistently elevated. Although the tumors in this series ranged in location from T-1 to L-1 and usually involved multiple segments, they were most frequently noted in the upper thoracic cord. Of the nine intradural lipomas, five were solely intramedullary whereas four also had an extramedullary component, Although some of these lesions appeared to be associated with cleavage planes at surgery and were encapsulated microscopically, complete surgical enucleation was difficult and was associated with severe morbidity. These tumors were characterized by a bland, monotonous histological pattern consisting of mature fat cells with admixed collagen and occasional microfoci of calcification. Five specimens contained admixed nerve bundles which were located predominantly at the margin; three of these cases contained concentric lamellae of Schwann cells around the nerves, with formation of onion-bulb structures. Admixed collagen with scattered fibroblast nuclei was present in eight specimens and was not restricted to the cases containing nerve bundles and Schwann cells. The nerve bundles were located predominantly at the periphery of the specimens suggesting secondary entrapment of adjacent nerve root structures by the anlage of the lipoma. The benign and noninvasive histological characteristics of the tumors support this interpretation. The associated hypertrophic onion-bulb formations probably represent degenerative and regenerative J. Neurosurg. / Volume44 / March, 1976
phenomena associated with compression of the entrapped nerves and Schwann cell proliferation. The lipomatous component of the tumors consisted of mature fat with no evidence of invasiveness or malignancy. Symptoms caused by the presence of such tumors may be related to the extent of the lipoma anlage and chronic compression of the cord. In our opinion, these tumors seem to be of hamartomatous origin. As it may be difficult to determine at surgery which lipomas have admixed nerve elements, a more prudent approach, including decompression and biopsy or subtotal removal, is indicated. Several hypotheses regarding the genesis of intradural spinal cord lipomas have been proposed; none, however, is entirely satisfactory. Some authors have postulated that these lesions are due to a developmental error with resultant inclusions of embryonic rests of fat cells during the formation of the neural tube whereas others feel that connective tissue metaplasia may lead to deposition of fat within the dura. ~ Although the true etiology has yet to be elucidated, many characteristics of these tumors suggest that they are of a hamartomatous origin. Although the hamartomatous anlage is presumably present at birth, the Slow growth potential of such lesions often results in formation of a symptomatic mass lesion much later in life, as noted in this series; similar late onset of symptoms is also associated with other hamartomatous lesions of the central nervous system. 335
B. J. Ammerman, et al. Acknowledgments The authors wish to thank Drs. H. H. Ammerman, F. Jannotta, and D. R. Smith for their help in preparing this manuscript.
References 1. Drapkin A J: High cervical intradural lipoma. J Neurosurg 41:699-704, 1974 2. Ehni G, Love JG: Intraspinal lipomas. Report of cases, review of the literature, and clinical and pathologic study. Arch Neurol Psychiatry 53:1-28, 1945 3. Guiffr6 R: Intradural spinal lipomas. Review of the literature (99 cases) and report of an additional case. Acta Neurochir 14:69-95, 1966 4. Pani KC, Chopra JS, Kak VK: Intramedullary lipoma of the spinal cord. Neurochirurgica (Stuttg) 15:33-35, 1972 5. Rubinstein LJ: Tumors of the central nervous system, in Atlas of Tumor Pathology. Washington, DC, Armed Forces Institute of Pathology, 1972, pp 56-74
336
6. Steinke CR: Spinal tumors: statistics on a series of 330 collected cases. J Nerv Meat Dis 47:418-426, 1918 7. Taniguchi T, Mufson JA: Intradural lipoma of the spinal cord. Report of a case. J Neurosurg 7:584-586, 1950 8. Thomas JE, Miller RH: Lipomatous tumors of the spinal canal. A study of their clinical range. Mayo Clin Proc 48:393-400, 1973 9. Webster H deF, SchrSder JM, Asbury AK, et al: The role of Schwann cells in the formation of "onion bulbs" found in chronic neuropathies. J Neuropathol Exp Neurol 26:276-279, 1967 The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. Address reprint requests to: Kenneth M. Earle, M.D., Department of Neuropathology, Armed Forces Institute of Pathology, Washington, D.C. 20306.
J. Neurosurg. / Volume 44 / March, 1976
Department of Neurological Surgery, The George Washington University Medical Center, Washington, D.C., and the Neuropathology Branch, Armed Forces Institute of Pathology, Washington, D.C. ~" Nine original cases of intradural spinal cord lipomas have been examined from a clinical and pathological standpoint. These tumors occur more commonly in men in the second to fourth decade and are found most frequently in the thoracic spinal cord. Paraparesis, sensory changes, urinary incontinence, and pain are frequent presenting complaints. Myelography is the diagnostic study of choice. All lipomas in this series were located primarily within the cord; four of these also presented an extramedullary extension. Admixed nerve bundles were present in five cases with associated hypertrophic onion-bulb formations in three. Decompression with biopsy or subtotal resection is the operative procedure of choice. KEY WORDS 9 lipoma 9 spinal cord neoplasm 9 intradural lipoma 9 onion-bulb formation 9 hamartoma
I
NTRADURAL spinal cord lipomas are encountered infrequently by the clinician or pathologist, since they occur in less than 1% of all spinal cord tumors? Although several authors have described their clinical experience with such lesions, complete clinicopathological correlation is available for only a small number of cases. 1'2,4'6 8 This paper presents the clinical and morphological findings based on a review of nine original cases of intradural spinal lipomas, and represents one of the largest available series of completely documented cases.
J. Neurosurg. / Volume44 / March, 1976
S u m m a r y of Cases
Clinical Material Nine cases of intradural spinal cord lipomas were reviewed including seven patients from the files of the Armed Forces Institute of Pathology and two from The George Washington University Medical Center. Only cases with verified intradural lesions were selected. Hematoxylin and eosin stains were employed routinely for microscopic evaluation in each case. One case 331
B. J. Ammerman, et al. TABLE 1 Presenting signs and symptoms in nine patients
Signs and Symptoms
No. of Cases
paraparesis long tract signs sensory changes urinary incontinence pain unilateral extremityweakness impotence
6 4 4 3 3 2 1
bral bodies, or pedicular destruction. No associated developmental defects in the vertebrae were noted. Myelography, performed in seven cases, revealed a complete block to the flow of contrast media in two and defects in the remaining five patients. Cerebrospinal fluid protein levels were recorded in four cases and were uniformly elevated, ranging from 72 to 1660 mg%. Tumor location ranged from T-I to L-I (Table 2); there were no cervical lesions in this series. The most frequent area of involvement was the upper thoracic cord, although the tumor often extended for several segments within the cord. The tumor was located exclusively within the cord in five instances, while four cases were associated with an extramedullary component. The surgical procedures consisted of decompressive laminectomy with biopsy and/or subtotal resection in five patients, and decompressive laminectomy with total excision in two. Operative reports were not available in two cases. The postoperative status of the patient appeared to be related to the extent of surgical removal. Both patients with total excision were paraplegic post-operatively, whereas all patients with sub-total resection or biopsy showed either improvement or minimal deterioration of preoperative status. All patients were followed for at least I year and none demonstrated a recurrence within this time.
(Case 6) was also studied with electron microscopy. Seven of these nine cases of intradural spinal lipomas occurred in males. The average age at time of diagnosis was 37 years, with a range of 2 to 73 years; seven of the patients were first seen between 25 and 50 years of age. Most patients had been symptomatic for about 2 years before seeking medical attention. There was no suggestion of a familial incidence in any of these cases. Presenting signs and symptoms are given in Table 1. Paraparesis ranged from mild to moderate, although no patient was paraplegic at the time of initial examination. Sensory disturbances included sensory levels to pinprick, diminished position and vibratory appreciation, and paresthesias. Urinary incontinence was intermittent and no patient had loss of bowel control. Pain, when present, was generally localized to the involved area of the thoracic or the thoracolumbar spine and Representative Case Reports was not radicular in nature. Two patients treated with differing degrees Complete spine x-ray films were available of surgical extirpation are described. Case 9 in three cases. None revealed changes emphasizes the favorable result which may be associated with mass lesions, such as widen- obtained by decompression and conservative ing of the spinal canal, scalloping of the verte- removal of intradural lipomas of the spinal cord; Case 5 illustrates the severe morbidity associated with a more radical procedure. TABLE 2 Case 9. This 46-year-old woman presented with back pain, occasional numbness of the Level and location of lipomas in nine patients right thigh, and intermittent urinary inconCase tinence for a period of several years. Physical No. Level Location examination revealed no sensory, motor, or intramedullary 1 T2-5 reflex abnormalities. Cystometrogram find2 T3--4 intramedullaryand extramedullary ings were consistent with a neurogenic 3 T-12 intramedullaryand extramedullary bladder. At myelography a defect was noted 4 T-3-L-1 intramedullary at T-11 and, at surgical exploration, a tumor 5 T6-8 intrameduUary extending from T-10 to T-12 was seen. The 6 T4-6 intramedullary 7 T-1 intramedullaryand extramedullary lipoma was located within the cord while an intramedullary 8 T-4 extramedullary extension was noted pos9 T10-12 intramedullaryand extramedullary teriorly. The tumor was subtotally excised as 332
J. Neurosurg. / Volume 44 / March, 1976
I n t r a d u r a l lipornas of t h e spinal c o r d it merged imperceptibly with the spinal cord parenchyma. Postoperatively the patient had no additional neurological deficit. Case 5. This 37-year-old man presented with a 3-year history of impotence and 2 years of progressive paraparesis with numbness of the right leg. A sensory level was noted at T-8 and bilateral Babinski signs were present. Myelography revealed an intramedullary lesion that extended from T-6 to T8. Surgery confirmed the intramedullary location of the tumor and a total excision was performed. Postoperatively the patient was paraplegic and incontinent.
Morphology Gross Appearance. A composite description of gross features made at the time of surgery or pathological examination follows. Lipomas of the spinal cord chaacteristically present as soft, yellow, fusiform tumors which occupy a portion of the spinal cord parenchyma. The intraparenchymal margins are frequently indistinct, and adjacent nerve roots may also be incorporated into the lesion, which may extend for several segments within the cord. Although the pertinent literature indicates that all portions of the cord may be involved, the lesions described in this series were located predominantly in the thoracic cord. Microscopic Examination. Nine specimens of variable size were available for histological examination; one specimen (from Case 6) was also examined with the electron microscope to evaluate the relationship of the lipoma to admixed nerve bundles and related hypertrophic onion-bulb formations. The major portion of each biopsy specimen was composed of large, regular, polygonal, reticulated, optically-empty spaces with delicate cytoplasmic membranes and unremarkable, eccentric nuclei consistent with mature fat. There was no microscopic evidence of immature or poorly-differentiated fat cells, pleomorphism, mitotic activity, or parenchymal invasion, and the histological impression was that of an inert, benign neoplasm or hamartoma (Fig. 1). Five cases contained admixed nerve bundles of variable size which were located predominantly at the periphery of the lesion and which were consistent with entrapped spinal nerve roots (Fig. 2). The nerve bundles in two cases were associated with prominent spindle cells which J. Neurosurg. / Volume44 / March, 1976
FIG. 1. Photomicrograph showing mature fat and entrapped nerve bundles. H & E, X 22. were morphologically consistent with Schwann cells. In three cases, the spindle cells were arranged around the axons in concentric lameUae that resulted in the formation of typical onion-bulb structures (Fig. 3), which have been described as a nonspecific feature associated with a variety of chronic, hypertrophic neuropathies? Eight of the cases contained remnants of a thin but distinct fibrous capsule at the margin of the biopsy, and an equal number contained various degrees of admixed collagen. Two cases showed small microfoci of calcification. Small aggregates of lipid-laden macrophages were occasionally seen in the periphery of the lesions. Vascularity was not abundant in these specimens, and was proportional to the amount of supporting stroma within the
FtG. 2. Photomicrograph showing full section of lesion containing collagen, mature fat, and entrapped, hypertrophic nerve bundles (arrow). H&E, X8. 333
B. J. Ammerman, et al. TABLE 3 Morphological features in nhle cases of intradural lipomas of the spinal cord
Case No.
Fat
Nerve Bundles
Onion Bulbs
1 2 3 4 5 6 7 8 9
mature mature mature mature mature mature mature mature mature
prominent moderate minimal none minimal prominent none none none
prominent none none none minimal prominent none none none
SpindleCells Capsule Collagen Calcification Lipid-laden (SchwannCells) Macrophages prominent minimal none none moderate prominent none none none
lesions. There was no pattern of angiolipoma among these cases (Table 3). Ultrastructure
Formalin-fixed tumor tissue was minced, osmicated, dehydrated in a series of graded alcohols, and embedded in Epon 812. Thick sections of 1 # were stained with toluidine blue and examined with the light microscope. The tissue consisted mostly of fat cells in which lay stellate-shaped aggregates of spindle-shaped cells. In one instance these
present present present present present present present none present
prominent none minimal minimal prominent moderate moderate moderate prominent
none none none none none microfoci none none microfoci
none none none present none none none none none
cells appeared to form a whorl around a round, finely-stippled structure that measured approximately 8 # in diameter. Selected blocks were trimmed, thin sections were cut in the silver range with the LKB ultramicrotome, stained with uranyl acetate and lead citrate, and examined with the Siemens and Hitachi electron microscopes. Tissue preservation was quite poor as evidenced by rupture of plasma membranes, disintegration of cytoplasmic organdies, and wide separation of cells by spaces filled with granular and filamentous electron-dense material. Two general categories of cells could be identified. The predominant cell type was characterized by abundant intracytoplasmic round bodies which contained osmiophilic granular material with variable packing density. A second cell was found admixed which had an elongated nucleus, scanty cytoplasm, no evidence of the intracytoplasmic bodies described above, and a prominent basement membrane (Fig. 4). The ultrastructure of this cell is consistent with that of a Schwann cell.
Discussion
FIG. 3. Photomicrograph of hypertrophic onionbulb formations. H & E, • 180. 33,t
Nine original cases of intradural spinal cord lipomas have been presented with clinicopathological correlation. This lesion occurs more c o m m o n l y in men, as characterized by the 3:1 ratio in this series; other authors have noted a similar preponderance. 8'8 Most patients in this series were symptomatic for about 2 years prior to diagnosis and presented during the second, third, and fourth decades of life. Presenting complaints included paraparesis, sensory disturbances, urinary incontinence, and pain. Myelography is the diagnostic study of J. Neurosurg. / Volume 44 / March, 1976
Intradural lipomas of the spinal cord
FIG. 4. Electron micrograph of Schwann cell in hypertrophic onion-bulb formations illustrating basement membrane (arrows). Uranyl acetate and lead citrate, • 48,600.
choice for localization of this lesion. Cerebrospinal fluid protein was consistently elevated. Although the tumors in this series ranged in location from T-1 to L-1 and usually involved multiple segments, they were most frequently noted in the upper thoracic cord. Of the nine intradural lipomas, five were solely intramedullary whereas four also had an extramedullary component, Although some of these lesions appeared to be associated with cleavage planes at surgery and were encapsulated microscopically, complete surgical enucleation was difficult and was associated with severe morbidity. These tumors were characterized by a bland, monotonous histological pattern consisting of mature fat cells with admixed collagen and occasional microfoci of calcification. Five specimens contained admixed nerve bundles which were located predominantly at the margin; three of these cases contained concentric lamellae of Schwann cells around the nerves, with formation of onion-bulb structures. Admixed collagen with scattered fibroblast nuclei was present in eight specimens and was not restricted to the cases containing nerve bundles and Schwann cells. The nerve bundles were located predominantly at the periphery of the specimens suggesting secondary entrapment of adjacent nerve root structures by the anlage of the lipoma. The benign and noninvasive histological characteristics of the tumors support this interpretation. The associated hypertrophic onion-bulb formations probably represent degenerative and regenerative J. Neurosurg. / Volume44 / March, 1976
phenomena associated with compression of the entrapped nerves and Schwann cell proliferation. The lipomatous component of the tumors consisted of mature fat with no evidence of invasiveness or malignancy. Symptoms caused by the presence of such tumors may be related to the extent of the lipoma anlage and chronic compression of the cord. In our opinion, these tumors seem to be of hamartomatous origin. As it may be difficult to determine at surgery which lipomas have admixed nerve elements, a more prudent approach, including decompression and biopsy or subtotal removal, is indicated. Several hypotheses regarding the genesis of intradural spinal cord lipomas have been proposed; none, however, is entirely satisfactory. Some authors have postulated that these lesions are due to a developmental error with resultant inclusions of embryonic rests of fat cells during the formation of the neural tube whereas others feel that connective tissue metaplasia may lead to deposition of fat within the dura. ~ Although the true etiology has yet to be elucidated, many characteristics of these tumors suggest that they are of a hamartomatous origin. Although the hamartomatous anlage is presumably present at birth, the Slow growth potential of such lesions often results in formation of a symptomatic mass lesion much later in life, as noted in this series; similar late onset of symptoms is also associated with other hamartomatous lesions of the central nervous system. 335
B. J. Ammerman, et al. Acknowledgments The authors wish to thank Drs. H. H. Ammerman, F. Jannotta, and D. R. Smith for their help in preparing this manuscript.
References 1. Drapkin A J: High cervical intradural lipoma. J Neurosurg 41:699-704, 1974 2. Ehni G, Love JG: Intraspinal lipomas. Report of cases, review of the literature, and clinical and pathologic study. Arch Neurol Psychiatry 53:1-28, 1945 3. Guiffr6 R: Intradural spinal lipomas. Review of the literature (99 cases) and report of an additional case. Acta Neurochir 14:69-95, 1966 4. Pani KC, Chopra JS, Kak VK: Intramedullary lipoma of the spinal cord. Neurochirurgica (Stuttg) 15:33-35, 1972 5. Rubinstein LJ: Tumors of the central nervous system, in Atlas of Tumor Pathology. Washington, DC, Armed Forces Institute of Pathology, 1972, pp 56-74
336
6. Steinke CR: Spinal tumors: statistics on a series of 330 collected cases. J Nerv Meat Dis 47:418-426, 1918 7. Taniguchi T, Mufson JA: Intradural lipoma of the spinal cord. Report of a case. J Neurosurg 7:584-586, 1950 8. Thomas JE, Miller RH: Lipomatous tumors of the spinal canal. A study of their clinical range. Mayo Clin Proc 48:393-400, 1973 9. Webster H deF, SchrSder JM, Asbury AK, et al: The role of Schwann cells in the formation of "onion bulbs" found in chronic neuropathies. J Neuropathol Exp Neurol 26:276-279, 1967 The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. Address reprint requests to: Kenneth M. Earle, M.D., Department of Neuropathology, Armed Forces Institute of Pathology, Washington, D.C. 20306.
J. Neurosurg. / Volume 44 / March, 1976
