Thoracic intramedullary schwannomas are rare spinal cord tumors. Most of these tumors have been reported as a single lesion in the spinal cord. The authors report the first case of intramedullary schwannoma accompanying by extramedullary beads-like daughter masses of the thoracic spine. A 68-year-old male presented with walking disturbance and decreased sensation below T10 dermatome. Imaging workup revealed an intramedullary mass at T6 and T7. T6 and T7 laminectomy and mass removal were performed. Intraoperatively, extramedullary beads-like daughter masses along the nerve roots adjacent to intramedullary mass were identified. Total removal of intramedullary lesion and partial resection of extramedullary masses were done. Histological analysis confirmed the diagnosis of schwannoma. The patient could ambulate independently at postoperative 1 month without any neurological sequelae. The authors experienced a surgical case of intramedullary schwannoma accompanying by extramedullary beads-like same pathologies in the thoracic spine.

Address for reprints : Chun-Kun Park, M.D. Ph.D., Neurosurgery Department, Seoul St. Mary's Hospital, The Catholic University, 505 Banpo-dong Seocho-gu, Seoul 137-040, Korea 
Tel : +82-2-2258-6127, Fax : +82-2-594-4248, E-mail : ckpmd@catholic.ac.kr

INTRODUCTION

   Spinal schwannomas are ones of the most common primary tumors of the spine, but intramedullary schwannomas in non-neurofibromatosis patients have been reported rarely, accounting for less than 1.1% of all schwannomas^{2,3,4,5,6,9,10,15)}. As previously stated, these lesions have appear as intramedullary single lesions or dumbbell intra- and extramedullary ones. 
   The authors report a case of an intramedullary schwannoma accompanied by extramedullary bead-like daughter masses in the thoracic spine.

CASE REPORT

   A 68-year-old male was admitted with a 17-month history of walking disturbance and decreased sensation below the T10 dermatome. He had no traumatic accident and no other previous disorders such as neurofibromatosis, or specific lesions on his skin. Neurological examination revealed that the motor function of both legs was grade 4/5. The sensation of all modalities below the T10 dermatomes was reduced. His bilateral knee and ankle jerks were hyperactive and continuous ankle clonus was observed. Gadolinium-enhanced magnetic resonance imaging (MRI) demonstrated an ill-demarcated, highly enhanced intramedullary ellipsoidal mass at the level from T6-7. A moderate spinal cord edema was also noted at the T3/4-9 level, and syrinx formation was noted above the mass. No abnormal enhancing lesion was present along the nerve root near the mass. The mass (6×7×30 mm) was located at the center of the spinal cord and was preoperatively considered to be intradural and intramedullary (Fig. 1, 2). 
   The operation was done with a standard posterior midline approach. Following skin incision and muscle dissection, T6 and T7 laminectomies were performed. When the dura and arachnoid were opened, an expanded thoracic cord and extramedullary bead-like masses along the adjacent nerve roots were identified (Fig. 3). The bead-like masses were firmly attached to the nerve roots and partially resected. The frozen section findings were consistent with a schwannoma. After the midline myelotomy, a dark brown intradural mass was seen. Frozen section findings of the intramedullary lesion were also defined as a schwannoma. The lesion was dissected off the spinal cord tissue and totally removed. The extramedullary and intramedullary masses were not connected. Intraoperative monitoring using motor-evoked potential was uneventful. After the operation, the patient's sensory and motor deficits gradually improved. A month after the operation, the patient could ambulate with no assistance. 
   Histological analysis confirmed the diagnosis of schwannoma. Immunocytochemical staining for S100 protein and silver was strongly positive, and staining for glial fibrillary acidic protein and epithelial membrane antigen was negative (Fig. 4). 

DISCUSSION

   Conti et al.⁴⁾ analyzed the literature from 1931 to 2002 and found only about 50 reported cases of non-neurofibroma related intramedullary schwannomas. Most of these lesions have been reported as single intramedullary lesions, and more rarely as dumbbell intra- and extramedullary ones. The present case of an intramedullary schwannoma is accompanied by bead-shaped multiple small schwannomas arising on the adjacent nerve roots, which are separated from each other. 
   Schwannomas originate from the Schwann cells. Schwann cells are absent in the central nervous system, thus it can explain the rarity of intramedullary schwannomas. The pathogenesis of intramedullary schwannoma is still not clear, and various hypotheses have been proposed. The postulated pathogeneses of these tumors' origin include Schwann cells along the intramedullary perivascular nervous plexus^7,14,16), focal intramedullary proliferation of Schwann cells in reaction to chronic disease or trauma^1,11), ectopic Schwann cells originating from migrating neural crest cells^8,12,17,18), and Schwann cells related to aberrant intramedullary myelin fibers¹¹⁾. Also, Schwann cells in the posterior nerve root at the root entry zone are assumed to be one of pathogeneses of intramedullary tumors^13,19). A tumor arising from Schwann cells in this "critical area," where the nerve root loses its sheath, could enter the subpial area in the spinal cord and appear as an intramedullary mass. The schwannomas in the present case consisted of an intramedullary large one and extramedullary bead-like small ones on the adjacent nerve roots. Although the masses were separated from each other, the pathogenesis of all masses would be the same in a single patient. These findings could support the hypothesis that intramedullary schwannomas originate from Schwann cells in the posterior nerve root at the root entry zone. 
   Complete surgical excision is the treatment of choice for spinal schwannomas, including intramedullary ones. In the present case, however, the authors could not completely remove all tumors. Although it was a simple matter to totally excise the intramedullary mass, there was no option but to partially resect the extramedullary bead-like masses because of their tight attachment to the nerve roots. The authors plan to follow this patient in the short term and treat him with radiotherapy if his tumors increase in size or recur.

CONCLUSION

   The authors experienced a surgical case of an intramedullary schwannoma accompanied by extramedullary bead-like masses of the same pathology in the thoracic spine. The present case could be helpful for understanding intramedullary schwannomas' pathogenesis. 

1. Adelman LS, Aronson SM : Intramedullary nerve fiber and Schwann cell proliferation within the spinal cord (schwannosis). Neurology 22 : 726-731, 1972

2. Brown KM, Dean A, Sharr MM : Thoracic intramedullary schwannoma. Neuropathol Appl Neurobiol 28 : 421-424, 2002

3. Char G, Cross JN : Intramedullary schwannoma of the spinal cord. West Indian Med J 36 : 35-38, 1987

4. Conti P, Pansini G, Mouchaty H, Capuano C, Conti R : Spinal neurinomas : retrospective analysis and long-term outcome of 179 consecutively operated cases and review of the literature. Surg Neurol 61 : 34-43; discussion 44, 2004

5. Drapkin AJ : Intramedullary schwannoma. J Neurosurg 75 : 834-835, 1991

6. Duong H, Tampieri D, Melancon D, Salazar A, Robert F, Alwatban J : Intramedullary schwannoma. Can Assoc Radiol J 46 : 179-182, 1995

7. Feigin I, Ogata J : Schwann cells and peripheral myelin within human central nervous tissues: the mesenchymal character of Schwann cells. J Neuropathol Exp Neurol 30 : 603-612, 1971

8. Herregodts P, Vloeberghs M, Schmedding E, Goossens A, Stadnik T, D'Haens J : Solitary dorsal intramedullary schwannoma. Case report. J Neurosurg 74 : 816-820, 1991

9. Kang JK, Song JU : Intramedullary spinal schwannoma. J Neurol Neurosurg Psychiatry 46 : 1154-1155, 1983

10. Kodama Y, Terae S, Hida K, Chu BC, Kaneko K, Miyasaka K : Intramedullary schwannoma of the spinal cord : report of two cases. Neuroradiology 43 : 567-571, 2001

11. Koeppen AH, Ordinario AT, Barron KD : Aberrant intramedullary peripheral nerve fibers. Arch Neurol 18 : 567-573, 1968

12. Marchese MJ, McDonald JV : Intramedullary melanotic schwannoma of the cervical spinal cord : report of a case. Surg Neurol 33 : 353-355, 1990

13. Mason TH, Keigher HA : Intramedullary spinal neurilemmoma: case report. J Neurosurg 29 : 414-416, 1968

14. Riggs HE, Clary WU : A case of intramedullary sheath cell tumor of the spinal cord; consideration of vascular nerves as a source of origin. J Neuropathol Exp Neurol 16 : 332-336, 1957

15. Ross DA, Edwards MS, Wilson CB : Intramedullary neurilemomas of the spinal cord : report of two cases and review of the literature. Neurosurgery 19 : 458-464, 1986

16. Shalit MN, Sandbank U : Cervical intramedullary schwannoma. Surg Neurol 16 : 61-64, 1981

17. Solomon RA, Handler MS, Sedelli RV, Stein BM : Intramedullary melanotic schwannoma of the cervicomedullary junction. Neurosurgery 20 : 36-38, 1987

18. Vailati G, Occhiogrosso M, Troccoli V : Intramedullary thoracic schwannoma. Surg Neurol 11 : 60-62, 1979

19. Wood WG, Rothman LM, Nussbaum BE : Intramedullary neurilemoma of the cervical spinal cord. Case report. J Neurosurg 42 : 465-468, 1975