Schwannoma¶
Definition¶
Schwannoma (neurilemmoma) is a benign nerve sheath tumor arising from Schwann cells. It is the most common intradural extramedullary spinal tumor and the most common spinal nerve sheath tumor overall. Schwannomas typically arise from a single nerve root fascicle and can be separated from the parent nerve at surgery, unlike neurofibromas which are intertwined with nerve fibers.
Imaging Findings¶
MRI¶
- Location — Intradural extramedullary mass, typically arising from a dorsal sensory nerve root. Most common in the lumbar and cervical spine.
- T1-weighted — Isointense to slightly hypointense relative to the cord
- T2-weighted — Hyperintense, often heterogeneous. Cystic changes, hemorrhage, and the "target sign" (peripheral high signal with central low signal) may be present.
- Enhancement — Intense, often homogeneous enhancement. Larger tumors may show heterogeneous enhancement with non-enhancing cystic/necrotic areas.
- CSF cap — CSF visible between the tumor and the cord, confirming extramedullary location
- Dumbbell morphology — May extend through the neural foramen into the paravertebral space (see Dumbbell Lesions)
- Foraminal widening — Smooth expansion of the neural foramen
CT¶
- Isodense to slightly hyperdense mass in the spinal canal
- Foraminal widening and smooth bony remodeling
- CT myelography can demonstrate the intradural mass as a filling defect
Clinical Pearl
The key MRI features distinguishing schwannoma from meningioma (the two most common intradural extramedullary tumors): Schwannomas arise from a nerve root (eccentric, may extend through the foramen as a dumbbell), are T2-hyperintense, and may be cystic. Meningiomas are dura-based (broad dural attachment), have a "dural tail" sign, and are more common in the thoracic spine in middle-aged women.
Multiple Schwannomas¶
Multiple spinal schwannomas should raise concern for schwannomatosis or neurofibromatosis type 2 (NF2). NF2 is associated with bilateral vestibular schwannomas, multiple spinal schwannomas, and meningiomas.
Management¶
- Surgical excision with nerve-sparing technique (schwannomas can be separated from the parent nerve)
- Recurrence is rare after complete excision
- Stereotactic radiosurgery for surgically inaccessible lesions
Key Points¶
- Most common intradural extramedullary spinal tumor
- Arises from Schwann cells of the dorsal sensory nerve root
- T2-hyperintense, avidly enhancing, may have cystic components
- Dumbbell extension through the neural foramen is characteristic
- Can be separated from the parent nerve at surgery (unlike neurofibroma)
- Multiple schwannomas suggest NF2 or schwannomatosis
References¶
- Koeller KK, Shih RY. Intradural extramedullary spinal neoplasms: radiologic-pathologic correlation. RadioGraphics. 2019;39(2):468-490. doi:10.1148/rg.2019180200.
- Davis DD, Kane SM. Neurilemmoma. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK560827/
- Lee JH, Kim HS, Yoon YC, Cha MJ, Lee SH, Kim ES. Differentiating between spinal schwannomas and meningiomas using MRI: a focus on cystic change. PLoS One. 2020;15(5):e0233623. doi:10.1371/journal.pone.0233623.
- Takashima H, Takebayashi T, Yoshimoto M, Onodera M, Terashima Y, Iesato N, et al. Differentiating spinal intradural-extramedullary schwannoma from meningioma using MRI T2 weighted images. Br J Radiol. 2018;91(1092):20180262. doi:10.1259/bjr.20180262.
- Koontz NA, Wiens AL, Agarwal A, Hingtgen CM, Emerson RE, Mosier KM. Schwannomatosis: the overlooked neurofibromatosis? AJR Am J Roentgenol. 2013;200(6):W646-W653. doi:10.2214/AJR.12.8577.
- Evans DG. NF2-related schwannomatosis. In: Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 1998 [updated 2023 Apr 20]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1201/
- Gaillard F, et al. Spinal schwannoma. Radiopaedia.org. Available from: https://radiopaedia.org/articles/spinal-schwannoma