A parotid mass with a misleading cytology
A 48-year-old woman has a 2.2 cm mobile, painless mass in the tail of the right parotid. Fine-needle aspiration is reported as 'benign salivary epithelium, consistent with pleomorphic adenoma.' She is scheduled for superficial parotidectomy. At surgery, the mass is well circumscribed but the facial nerve is draped over it; frozen section is requested. The frozen section shows a biphasic tumor with tubules and a prominent lymphoid stroma; the surgeon asks whether to proceed with parotidectomy or stop.
1. How should the frozen-section findings alter the surgical plan, and what is the pitfall in the original cytology?
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The frozen section description - biphasic tubules within a lymphoid stroma - suggests Warthin tumor (papillary cystadenoma lymphomatosum), not pleomorphic adenoma. Warthin tumors are benign and, when well circumscribed, can be managed by local excision/enucleation with a margin rather than superficial parotidectomy, sparing facial nerve dissection where feasible.
The pitfall: FNA of Warthin tumor often yields oncocytic/benign-appearing epithelium and lymphocytes, and can be misread as pleomorphic adenoma or 'benign salivary epithelium.' The judgment is to treat the frozen section as decisive for the architectural diagnosis and avoid unnecessary nerve dissection, while confirming on permanent sections.
2. What would you do if the permanent sections instead showed a tumor with perineural invasion and a cribriform architecture?
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That combination raises adenoid cystic carcinoma (cribriform 'Swiss cheese' pattern, perineural invasion). Management changes to:
- Wider resection with margin control, given perineural spread.
- Consideration of postoperative radiotherapy, particularly for perineural invasion, close margins, or higher-grade features.
- Imaging of the nerve pathway (MRI along cranial nerve VII) and longer follow-up, because late recurrence and distant metastasis are characteristic.
Key judgment: perineural invasion is a management-changing finding even when the tumor looks well circumscribed grossly; it should trigger both wider margins and adjuvant therapy planning.