## Distinguishing Vestibular Schwannoma from CPA Meningioma ### Anatomic and Imaging Basis **Key Point:** Vestibular schwannomas arise from the vestibular nerve within the internal auditory canal (IAC) and characteristically widen the IAC as they grow. Meningiomas arise from dura and typically do not enlarge the IAC. ### Comparative Table | Feature | Vestibular Schwannoma | CPA Meningioma | |---------|----------------------|----------------| | **Origin** | Vestibular nerve (IAC) | Dura/arachnoid | | **IAC involvement** | Widens IAC (90%) | Does not widen IAC | | **Dural tail** | Absent or minimal | Present (80%) | | **Enhancement** | Homogeneous | Homogeneous | | **T2 signal** | Hyperintense (cystic/edema) | Isointense to hyperintense | | **Location** | Arises within IAC | Arises from dura, lateral to IAC | | **Calcification** | Rare | Common (20–30%) | ### Mechanism **High-Yield:** The **widening of the internal auditory canal** is the most specific discriminator. Vestibular schwannomas originate from the vestibular nerve within the bony confines of the IAC and enlarge it as they grow. Meningiomas, arising from dura lateral to the IAC, do not cause IAC widening. **Mnemonic:** **SCHWANNOMA = CANAL WIDENING** — Schwannomas (nerve sheath tumors) enlarge the canal they arise from; meningiomas (dural tumors) do not. **Clinical Pearl:** On axial CT, measure the IAC diameter at the porus acusticus. A diameter >8 mm (or asymmetry >2 mm) suggests schwannoma. Meningiomas present as masses lateral to a normal-caliber IAC. ### Why This Matters IAC widening is a pathognomonic sign of vestibular schwannoma and guides diagnosis without ambiguity. Meningiomas require different surgical approaches and have different prognoses; accurate preoperative distinction is critical. 
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