Parotid intranodal metastasis of Merkel cell carcinoma: a rare case report.

Background: Merkel cell carcinoma is a rare, highly aggressive neuroendocrine skin tumor with a low incidence rate, typically arising on sun-exposed areas. This case report aims to describe an unusual metastatic pattern involving the parotid gland lymph nodes and to discuss treatment strategies, thereby raising awareness of the disease and providing clinical insights.

Case presentation: A 63-year-old female presented with a mass in the left parotid gland region persisting for two months. Clinical examination revealed a firm, well-defined, mobile mass measuring approximately 2.0 × 2.0 cm at the lower posterior pole of the left parotid gland, located behind the left ear. The mass was non-tender, without spontaneous pain, ulceration, redness, or local temperature elevation. The patient had previously undergone excision of an earlobe mass at another hospital without pathological examination. CT imaging demonstrated a space-occupying lesion in the left parotid gland. Under general anesthesia, the superficial lobe of the left parotid gland and the mass were excised. Postoperative paraffin histopathology and immunohistochemistry confirmed Merkel cell carcinoma with lymph node metastasis in the left parotid gland. A PET-CT scan performed 10 days postoperatively revealed no definite primary lesion and no distant metastasis. At present, the patient's systemic and local conditions remain stable.

Conclusion: The diagnosis of Merkel cell carcinoma is challenging due to its rarity and early metastatic tendency, often resulting in misdiagnosis or missed diagnosis. Although imaging studies assist in detecting metastatic lesions, parotid gland lymph node metastases may present with nonspecific features, leading to diagnostic confusion with other parotid diseases. Histopathological examination remains essential, and the complex immunohistochemical profile necessitates the use of multiple markers for accurate diagnosis.