Pigmented apocrine hidrocystoma of the caruncle

To describe the clinical and immunopathologic features of the first convincing apocrine hidrocystoma of the caruncle that happened to be pigmented.

Case report with clinical evaluation, ultrasound biomicroscopy, and paraffin-embedded tissue stained with hematoxylin and eosin, periodic acid-Schiff, and immunohistochemical markers.

Ultrasound biomicroscopy identified a cyst occurring in a 56-year-old white woman. Histopathologically, it was lined by an inner eosinophilic columnar epithelium that was gross cystic disease fluid protein-15-positive and evinced apical decapitation secretion and periodic acid-Schiff-positive, diastase-resistant cytoplasmic granules. Fontana- and MART-1-positive melanin granules were demonstrated. There was an outer layer of smooth muscle actin-positive myoepithelial cells. An adjacent apocrine gland was discovered with identical staining characteristics but without melanin granules.

Classical apocrine gland cysts can exceptionally develop in the caruncle. The light dispersion of cytoplasmic melanin found in the lining cells may have contributed to the cyst's clinical pigmentation, which is otherwise generally regarded as the result of the Tyndall effect, wherein blue wavelengths of light reflect from a colloidal solution of lipofuscin and cell debris.