A 48-year-old woman from Mumbai is referred to neurosurgery with a 2-year history of progressive right-sided facial pain, initially in the V2 distribution, now spreading to V1 and V3. She also reports gradual onset of numbness over the right cheek and upper lip over the past 6 months. MRI brain with contrast shows a mass at the cerebellopontine angle compressing the trigeminal nerve root entry zone. What is the most likely diagnosis?

Explanation

## Clinical Presentation of Symptomatic Trigeminal Neuralgia **Key Point:** When trigeminal neuralgia is accompanied by **progressive sensory loss** (hypoesthesia, paresthesia) and **progressive worsening** over months to years, a **secondary (symptomatic) cause** must be excluded. The most common structural lesions are schwannomas, meningiomas, and vascular malformations at the cerebellopontine angle (CPA). ## Differential Diagnosis of CPA Lesions Affecting CN V | Lesion | Origin | CN V Involvement | Associated Features | MRI Appearance | | --- | --- | --- | --- | --- | | **Trigeminal schwannoma** | CN V nerve sheath | Pain + progressive sensory loss | Isolated CN V; slow growth | T1 iso/hypointense; T2 hyperintense; enhances | | **Acoustic neuroma** | CN VIII (vestibular) | CN V compression (late) | Hearing loss, tinnitus, vertigo (CN VIII first) | Cerebellopontine angle; enhances | | **Meningioma** | Dura | CN V + other CNs | Broad dural base; may have hyperostosis | Dural tail sign; homogeneous enhancement | | **Epidermoid cyst** | Congenital inclusion | CN V compression (rare) | Non-enhancing; restricted diffusion | T1 hypointense; T2 hyperintense; no enhancement | ## Why This Patient Has Trigeminal Schwannoma 1. **Progressive sensory loss:** Trigeminal schwannomas cause progressive hypoesthesia and paresthesia — a hallmark feature absent in idiopathic TN. 2. **Expanding distribution:** Pain spreading from V2 → V1, V3 over time suggests a growing mass compressing the entire trigeminal nerve, not a functional disorder. 3. **Duration and progression:** 2-year progressive course with sensory changes is typical of a slow-growing nerve sheath tumour. 4. **Imaging finding:** Mass at the trigeminal nerve root entry zone — the exact anatomical location of a trigeminal schwannoma. 5. **Isolated CN V:** Unlike acoustic neuroma (CN VIII first, CN V late), trigeminal schwannoma presents with isolated CN V symptoms. **High-Yield:** Trigeminal schwannomas account for 0.8–1.5% of intracranial tumours and 5–8% of CPA lesions. They typically present with **pain + progressive sensory loss**, distinguishing them from idiopathic TN (pain alone, normal exam). ## Pathophysiology **Clinical Pearl:** Schwannomas arise from the nerve sheath (Schwann cells) and grow slowly, compressing the nerve axons. This causes both irritative symptoms (pain, paresthesia) and progressive loss of function (sensory loss, motor weakness if large). ## Management - **Observation:** Small, asymptomatic lesions may be monitored with serial MRI. - **Microsurgical resection:** Gold standard for symptomatic, enlarging tumours. - **Stereotactic radiosurgery:** Alternative for poor surgical candidates or recurrent disease. **Mnemonic: SCHWANN** — **S**low growth, **C**ranial nerve origin, **H**ypoesthesia (progressive), **W**ell-circumscribed, **A**ccounts for 5–8% of CPA lesions, **N**erve sheath origin, **N**ormal enhancement.