A 45-year-old female presents with a 2-year history of progressive unilateral hearing loss, tinnitus, and unsteadiness. An MRI scan reveals a well-defined tumor located in the cerebellopontine angle (CPA). A surgical resection is performed, and subsequent histopathological examination of the tumor tissue is given below. Based on these histopathological findings, what is the most likely diagnosis?

Explanation

## Correct Answer: A. Schwannoma Schwannoma (acoustic neuroma) is the classic CPA tumor presenting with the triad of progressive unilateral sensorineural hearing loss, tinnitus, and ataxia/unsteadiness. The tumor arises from the Schwann cells of the vestibulocochlear nerve (CN VIII), explaining the audiovestibular symptoms. Histopathologically, schwannomas are characterized by **Antoni A and B regions**: Antoni A areas show densely packed spindle cells with nuclear palisading (Verocay bodies—organized rows of nuclei separated by cell processes), while Antoni B regions contain loosely arranged cells with myxoid stroma. The tumor is benign, well-circumscribed, and encapsulated. The CPA location is pathognomonic—schwannomas account for 80–90% of CPA masses in adults. The progressive nature over 2 years and unilateral presentation further support this diagnosis. Immunohistochemistry shows strong S-100 positivity, confirming neural crest origin. In Indian clinical practice, vestibular schwannomas are managed conservatively (serial imaging) if asymptomatic or small, or surgically via translabyrinthine, retrosigmoid, or middle fossa approaches depending on hearing preservation goals and tumor size. ## Why the other options are wrong **B. Ependymoma** — Ependymomas arise from ependymal cells lining the ventricular system and are rare in the CPA. They typically present in children and young adults with hydrocephalus and intraventricular location. Histologically, they show perivascular rosettes and ependymal rosettes, not Verocay bodies. CPA location is extremely rare for ependymomas, making this a poor fit for the clinical and radiological presentation. **C. Neurofibroma** — Neurofibromas are benign tumors of nerve sheath origin but differ from schwannomas: they are infiltrative (not encapsulated), contain admixed axons, lack Verocay bodies, and show S-100 positivity only in the neurofibromatous component. While neurofibromas can occur in the CPA (especially in NF1), they are far less common than schwannomas. The well-defined, encapsulated appearance on MRI and the histological description of organized Verocay bodies favor schwannoma over neurofibroma. **D. Meningioma** — Meningiomas are the second most common CPA tumor (10–15% of cases) but arise from arachnoid cap cells, not nerve sheath. Histologically, meningiomas show whorled patterns, psammoma bodies, and meningothelial cells—not spindle cells with Verocay bodies. Meningiomas typically present with CN V and VII involvement before CN VIII and are often dural-based. The absence of meningothelial architecture and presence of Verocay bodies exclude meningioma. ## High-Yield Facts - **Schwannoma (acoustic neuroma)** accounts for 80–90% of cerebellopontine angle masses in adults. - **Verocay bodies** (organized nuclear palisades) and **Antoni A/B regions** are pathognomonic histological features of schwannoma. - **CN VIII involvement** (unilateral SNHL + tinnitus + vestibular dysfunction) is the classic clinical triad for vestibular schwannoma. - **S-100 positivity** on immunohistochemistry confirms neural crest origin and distinguishes schwannoma from meningioma. - **Well-circumscribed, encapsulated tumor** on imaging is typical; neurofibromas are infiltrative and lack clear demarcation. - **Retrosigmoid approach** is preferred in India for hearing-preserving surgery; translabyrinthine for large tumors with poor preoperative hearing. ## Mnemonics **CPA Tumors: 8-8-80 Rule** 8% meningioma, 8% other (ependymoma, choroid plexus, etc.), 80% schwannoma. Schwannoma dominates the CPA differential. **Schwannoma Histology: VEIN** **V**erocay bodies, **E**ncapsulated, **I**nfiltration absent, **N**uclear palisading. Distinguishes from neurofibroma (infiltrative, no Verocay bodies). **CN VIII Schwannoma: HTA** **H**earing loss (SNHL), **T**innitus, **A**taxia/Ataxia. The classic triad that should trigger CPA imaging. ## NBE Trap NBE may pair "CPA tumor" with "neurofibroma" to trap students who confuse nerve sheath tumors; however, the histological description of Verocay bodies and encapsulation is specific to schwannoma, not neurofibroma. The well-defined appearance on MRI further excludes the infiltrative nature of neurofibroma. ## Clinical Pearl In Indian tertiary centers, vestibular schwannomas are increasingly diagnosed on MRI before symptom progression. Watchful waiting with serial imaging is standard for small, asymptomatic tumors; surgery is reserved for symptomatic or enlarging lesions. The retrosigmoid approach is preferred when hearing preservation is a goal, especially in younger patients. _Reference: Robbins & Cotran Pathologic Basis of Disease, Ch. 28 (Nervous System); Bailey & Love's Short Practice of Surgery, Ch. 51 (Neurosurgery)_