Ciliated and Mucinous Adenomatous Syringometaplasia: The Missing Link of the "Ciliated Eccrine Metaplasia" Theory in the Histogenesis of Cutaneous Eccrine Ciliated Cyst?

A variety of metaplastic changes has been reported in eccrine ducts and glands with squamous and mucinous syringometaplasia representing the most common histopathologic patterns. In the current case, a previously unreported variant of syringometaplasia was described in a female newborn with a 2-cm occipital cutaneous defect consistent with cutis aplasia. Over a more than 1-year period of local treatment, an enlarging plaque associated with local alopecia developed at the site of the original ulcerated area. A local excision demonstrated a superficial hypertrophic scar associated with a complete loss of hair follicles. In addition, there was a proliferation of eccrine glands and ducts lined by cuboidal epithelial cells arranged in a linear distribution beneath the scar area. Focal anastomosing of the proliferative ducts was identified. In few dilated ducts, the epithelial lining was composed of an inner layer of columnar cells with well-formed apical cilia and intracytoplasmic mucin and an outer layer of myoepithelial cells. The mucinous and ciliated cells were positive for epithelial membranous antigen and carcinoembryonic antigen, but negative for estrogen receptors, progesterone receptors, and thyroid transcription factor-1. Because this variant of eccrine metaplasia has not hitherto been reported in the literature, the term ciliated and mucinous adenomatous syringometaplasia was proposed for this unusual histologic finding. Mucinous and ciliated adenomatous syringometaplasia not only expands the spectrum of metaplastic changes in sweat gland units, but also might represent the missing link in the histogenesis of a subset of cutaneous ciliated cysts.