Cystic Giant Sacral Schwannoma Mimicking Aneurysmal Bone Cyst : A Case Report and Review of Literatures
A 54-year-old man visited the outpatient clinic complaining tingling sensation and paresthesia of left lower limb for several years. His symptoms have been aggravated during the last several months and there has been no improvement after conservative cares. He had no history of previous trauma or constitutional symptoms. Neurologic examination revealed weakness of dorsiflexion and plantaflexion on the left foot with mild hypesthesia at the left S1 dermatome. Perineal and perianal sensations were also mildly decreased.\nPlain radiograph showed an osteolytic lesion limited to left sacral ala sparing lumbar spine (). Magnetic resonance (MR) imaging of lumbar spine revealed about 5.1×3.4×3.6 cm sized multilocular cystic mass with canal invasion and bone erosion of the left S1 body. The mass showed homogenous hypointense signal on T1-weighted image and hyperintense signal on T2-weighted image. The lesion showed multi-septated cystic rim enhancement after administration of gadolinium contrast, but no definite solid portion was found. The left S1 root was also obliterated, which seemed to be main cause of leg symptoms. No extraspinal component was identified (). Computer tomography (CT) myelography was performed and intraosseous expensile mass involving left sacrum was presented along with left S1 root compression and displacement of the left sacral nerves below. A subtle pathologic fracture involving upper endplate of S1 was also noted ().\nThe initial preoperative diagnosis was ABC, with several radiologic clues such as the location of mass, which was presenting in sacrum and compromising the neural arch, near totally cystic nature and balloon-like expanslile remodeling of bone. Even fluid-fluid level was not revealed in the imaging studies, ABC was strongly suspected.\nWe underwent a grossly-total tumor resection with lumbosacral reconstruction via posterior approach. A well-defined, encapsulated, cystic mass was found in epidural space adherent to nerve sheath displacing sacral nerve roots peripherally. The borders of tumor was carefully identified and dissected to preserve capsule of the cystic component under operating microscope. Once pericapsular dissection was done, en-bloc tumor resection was followed and sacral nerve roots were successfully preserved under spontaneous and evoked electromyography monitoring (). Since more than half of S1 body had been eroded by the tumor, an instrumented stabilization with fixation from L4 to the ilium (iliac screws) was performed ().\nAfter the operation, the patient was completely recovered from the preoperative symptoms without any neurologic deterioration (). Histological examinations confirmed the diagnosis of cystic schwannoma with both Antoni A and Antoni B growth patterns in a fibrillar background (). Verocay bodies were noted, and the tumor cells were reactive to S-100 protein antibody.\nThe patient was discharged at 1 week after the operation without any complications. Outpatient clinic follow-up for 6 month showed no symptom recurrence and the patient was tolerable. Serial follow-up X-rays at 3 and 6 month after surgery showed no implant-related complications.