Partially Cystic Lumbar Schwannoma with Atypical Histopathologic Features

Spinal schwannomas are benign nerve sheath neoplasms that constitute about 30% of extramedullary spinal cord tumors. They are usually small, well-encapsulated tumors with low mitotic activity and concurrently carry a low risk of recurrence. Here, we report a case of atypical histologic variant of spinal schwannoma that had higher cellular density, nuclear atypia, and lack of encapsulation. To our best knowledge, no such cases of this atypical variant with regards to lumbar spine have been reported in the literature.

A 66-year-old male had an incidental left-sided paraspinal mass discovered while undergoing workup for cholecystitis. On examination, the patient was neurologically intact. Imaging revealed the presence of a contrast-enhanced, partially cystic mass arising from the L3-4 intervertebral foramen and causing left psoas muscle displacement. A minimally invasive left L3-4 posterior extracavitary resection was done. Histopathologic examination revealed a partly unencapsulated tumor with higher than usual cellular density and nuclear atypia, resulting in a diagnosis of "atypical schwannoma." Imaging at 6 months' follow-up showed stable postsurgical changes and residual tumor with no evidence of progression/recurrence.

Atypical schwannoma has higher cellular density and nuclear atypia and lacks encapsulation. A review of the literature suggests an increased risk of recurrence when compared with typical variants, and complete tumor removal should be attempted.