Malignant Merkel cell neoplasm of the eyelid.

Malignant Merkel cell neoplasms of the eyelid are most commonly found in elderly patients. They occur most frequently on the upper eyelid and are seen as large, nontender , red or violaceous masses with intact overlying skin. Differential diagnosis includes lymphoma and oat cell carcinoma. Conventional light microscopic features are usually distinctive, but tissue should be saved for electron microscopy and immunocytochemical studies, since the presence of dense-core neurosecretory granules and perinuclear microfilaments on electron microscopic examination and positive staining for neuron-specific enolase, are strongly suggestive of malignant Merkel cell neoplasm. Because of the diffuse infiltrative growth pattern and early lymphatic spread of this tumor, treatment requires careful examination of regional lymph nodes and wide surgical excision of the tumor with frozen-section control of margins.