Merkel Cell Carcinoma of Eyelid (MCC)

Merkel cell carcinoma (MCC) of the eyelid is a highly aggressive malignant primary cutaneous neuroendocrine tumor. Risk factors include advanced age, male gender, fairskinned, immunocompromise, sun exposure, polyomavirus infection. It usually presents as rapidly progressive violaceous nodule with or without ulceration. Differential diagnosis includes chalazion, cellulitis, capillary hemangioma, squamous cell carcinoma, basal cell carcinoma, sebaceous cell carcinoma. Biopsy is necessary for definitive diagnosis. Sentinel lymph node biopsy (SLNB) is required for detecting nodal metastases. Histopathologically, MCC is a small round blue cell tumor, positive for neuroendocrine markers (CD56, synaptophysin, chromogranin, and INSM1) and for cytokeratin 20. Surgical excision is the mainstay of treatment. Adjuvant radiotherapy is needed for local control, and chemotherapy is used in systemic involvement. MCC has a poor prognosis with relatively high mortality rate, especially in patients with distant metastases. On NECT, the mass is usually hyperdense due to its high cellular density, and enhancement varies depending on the aggressiveness of the tumor. The imaging features on MR also vary according to the literature. Some describe them as inhomogeneous on T1 and T2. These tumors usually enhance following contrast administration; the internal features may depend on the amount of necrosis and cystic degeneration. The hypercellular elements of the lesion will show restriction on DWI. Advanced disease may involve subcutaneous nodular spread and extra-capsular fatty stranding.