Cytodiagnosis of Mammary Schwannoma: A Ride on a Swing—A Curious Report of Two Cases

Abstract

Mammary schwannoma is an exceptionally rare benign peripheral nerve sheath tumor, accounting for nearly 2.6% of all benign neurogenic tumors and only 0.2% of all breast tumors. Cytological diagnosis of this entity is exceedingly uncommon, with very few cases reported in literature. We report two rare cases of mammary schwannoma from North India presenting as progressively enlarging, well-circumscribed, firm, and mobile breast lumps. Clinical examination and ultrasonography in both cases suggested fibroadenoma (BI-RADS 2). Fine-needle aspiration cytology (FNAC) yielded richly cellular smears composed of spindle cells with wavy nuclei arranged in fascicles. One case additionally demonstrated characteristic Verocay bodies, providing an important cytological clue toward schwannoma. Based on the triple assessment approach and cytomorphological findings, both lesions were categorized as benign (Category 2) according to the International Academy of Cytology Yokohama System and diagnosed as mammary schwannoma. Subsequent excision specimens showed encapsulated tumors with typical Antoni A and Antoni B areas on histopathology. Diffuse S-100 immunopositivity further confirmed the diagnosis. These cases highlight the importance of considering schwannoma in the differential diagnosis of benign spindle cell lesions of the breast. FNAC, when performed skillfully and interpreted carefully, serves as a simple, minimally invasive, and cost-effective modality for accurate preoperative diagnosis of this exceptionally rare entity. Recognition of Verocay bodies can significantly aid in cytodiagnosis and guide appropriate surgical management.