Filum terminale schwannoma with new onset of severe low back pain and radiculopathy: illustrative case

Abstract

Background: Schwannomas are CNS WHO grade 1 benign peripheral nerve sheath tumors. They can occur anywhere in the body where there are peripheral nerves, but they are most common in the vestibular system. To the authors' knowledge, there has been only one previous report of their presentation in the filum terminale.

Observations: The author present the case of a 36-year-old man who presented to the emergency department with acute-on-chronic right low back pain and shooting pain to his right groin with radiation to his knee. He was found to have an L1-2 intradural extramedullary lesion on MRI abutting the conus. His preoperative neurological examination was otherwise unremarkable, and he was promptly taken for L1-2 laminectomy and resection of the lesion. Final pathological diagnosis was intradural extramedullary cellular schwannoma, CNS WHO grade 1, of the filum terminale. Postoperative MRI demonstrated gross-total resection. The patient had new urinary fullness and constipation, which resolved by the 2-month follow-up, and otherwise recovered well with resolution of his back and leg pain.

Lessons: This case illustrates a rare presentation of an intradural extramedullary cellular schwannoma at the filum terminale, emphasizing the importance of a broad differential diagnosis. Resection of these neoplasms offers a definitive and safe treatment. https://thejns.org/doi/10.3171/CASE25333.

Keywords: filum terminale schwannoma; lumbar spine tumor; nerve sheath tumor; spine surgery.

FIG. 1.

T2-weighted axial (A) and sagittal (B) MR images of the lumbar spine without intravenous contrast at presentation. T1-weighted postcontrast axial (C) and sagittal (D) MR images of the lumbar spine at presentation. Imaging demonstrates a contrast-enhancing, heterogeneous cystic, and solid-appearing 3.4 × 1.3 × 1.5–cm intradural lesion centered at approximately the L1–2 disc space. The lesion is immediately below the conus medullaris (which terminates at the upper aspect of L1) and displaces the cauda equina nerve roots. The cauda equina nerve roots in the remaining lumbar spine appear unremarkable without other lesions.

FIG. 2.

Intraoperative microscope images. A: A large cystic-appearing heterogeneously composed intradural extramedullary lesion exposed within the cauda equina. B and C:Rostral (B; arrow directed toward rostral filum terminale) and caudal (C; arrow directed toward caudal filum terminale) views of the debulked tumor, exposing the origin of the tumor from the filum terminale with clear rostral and caudal connections to the ventral aspect of the tumor. D: The operative bed after gross-total resection of the lesion without any obvious residual tumor.

FIG. 3.

Pathological features of this cellular schwannoma. A: Hematoxylin and eosin (H&E) section of the neoplasm demonstrating that it is moderately densely cellular and entirely composed of compact tissue, also known as Antoni A tissue, that consists of spindle cells with mildly plump nuclei arranged in interweaving fascicles. Mitotic activity is not evident. B: Immunohistochemical stain for S100 protein demonstrating diffuse brown labeling of the neoplasm, which supports its identity as a peripheral nerve sheath tumor. C: In this area of the H&E section, the attenuated peripheral nerve is located at the periphery of the tumor. The peripheral nerve tissue has a minimally more pink color than the tumor, and some dots that are visible in this area are axons in cross-section. The capsule is identified by arrows. D: Immunohistochemical analysis for neurofilament protein highlighting the axons, which are stained brown, in the attenuated peripheral nerve that is located in the subcapsular region of the neoplasm. Original magnification ×200 (A–D).

FIG. 4.

Two-month postoperative T2-weighted axial (A) and sagittal (B) MR images of the lumbar spine without intravenous contrast. Two-month postoperative T1-weighted postcontrast axial (C) and sagittal (D) MR images of the lumbar spine. The images demonstrate interval L1–2 posterior laminectomy and resection of the prior intradural mass with evolving postprocedural changes. Slight associated clumping of the cauda equina nerve roots with nodular areas of enhancement in the region of the cauda equina represent evolving postprocedural changes. Appearance of gross-total resection.