Apocrine Papillary Hidrocystoma With Mucinous Metaplasia (Goblet Cell Type): A Case Report and Review of the Literature.

Mucinous metaplasia (goblet cell type) is exceptionally rare in the skin. This is the second case of apocrine papillary hidrocystoma with mucinous metaplasia (goblet cell type) and a review of the literature exploring the significance and frequency of mucinous metaplasia with goblet cells in nongenital skin. The patient is an elderly man who presented with a blue-pigmented nodule on the scalp that was clinically suggestive of an atypical nevus. Histologically, the lesion was composed of a simple cyst of cuboidal cells with decapitation secretion and mucinous metaplasia with goblet cells. Papillary formation was identified in the cysts. Most cases of cutaneous mucinous metaplasia have been reported on genital skin, usually after chronic inflammation of the area. This type of mucinous metaplasia is categorized as benign mucinous metaplasia of the genitalia (BMM) and is believed to be unrelated to apocrine glands owing to the different histologic features and absence of apocrine differentiation by immunohistochemistry. Mucinous metaplasia (goblet cell type) has been previously reported in benign adnexal tumors (eccrine acrospiroma/hidroadenoma, mixed tumor, and syringocystadenoma papilliferum) and in malignant tumors (apocrine hidradenocarcinoma and squamous cell carcinoma). To date, mucinous metaplasia has not been identified in the histologically normal apocrine glands.