Introduction
Schwannomas are benign, slow-growing peripheral nerve sheath tumors that arise from Schwann cells. They can occur anywhere in the body but are most frequently seen in the head and neck region, particularly involving the vestibulocochlear nerve (acoustic schwannoma/vestibular schwannoma). Although histology is the gold standard, radiology plays a vital role in diagnosis, surgical planning, and follow-up.
Imaging Features of Schwannoma
CT Findings
- Well-defined, round or oval soft-tissue attenuation mass.
- May show bony remodeling or expansion if arising from skull base or foramina.
- Calcification is rare.
MRI Findings (Modality of choice)
- T1-weighted: Iso- to hypointense relative to muscle.
- T2-weighted: Hyperintense, often with a “target sign” (central low signal with peripheral high signal).
- Contrast enhancement: Intense, usually homogeneous, but may be heterogeneous in larger lesions with cystic degeneration.
- Diffusion: Typically no restricted diffusion (helps differentiate from malignant tumors).
Vestibular Schwannoma (Acoustic Neuroma)
- Expands the internal auditory canal (IAC).
- “Ice-cream cone appearance”: tumor in the IAC (cone) with extension into the cerebellopontine angle cistern (scoop).
- Important to assess relation to brainstem and cranial nerves.
Differential Diagnosis
Radiological mimics include:
- Neurofibroma (fusiform, no capsule, often associated with NF1).
- Meningioma (dural tail sign, calcification, hyperostosis).
- Paraganglioma (salt-and-pepper appearance on MRI).
Role of Radiology in Management
- Pre-operative planning: Defines tumor extent and relation to nerves, vessels, and bone.
- Follow-up: Detects residual or recurrent disease after surgical excision or stereotactic radiosurgery.
- Screening: In patients with neurofibromatosis type 2 (NF2), MRI is crucial for detecting bilateral vestibular schwannomas.
Teaching Points
- Schwannoma = benign, encapsulated, eccentric nerve sheath tumor.
- MRI is the gold standard for diagnosis and follow-up.
- Always differentiate from meningioma and neurofibroma for proper surgical planning.
Conclusion
Schwannomas are benign tumors with classic imaging characteristics that radiologists must recognize. Early and accurate diagnosis helps in preserving nerve function and planning minimally invasive surgical or radiosurgical interventions.
