Trichilemmal Cysts With Divergent Ductal Differentiation: A Series of 4 Cases

The study "Trichilemmal Cysts With Divergent Ductal Differentiation: A Series of 4 Cases" conducted by Khan, Fraga, and Dai in 2020, examined the clinicopathological characteristics of sweat duct differentiation in trichilemmal cysts. The researchers reviewed 411 cases of trichilemmal cyst diagnosed at their institution between 2008 and 2019. They found ductal structures in 4 cases (0.97%), involving 2 male and 2 female patients aged 34-55. The ducts were lined by attenuated epithelial cells and were immunoreactive for polyclonal carcinoembryonic antigen and cytokeratin 7. Ductal differentiation involved a median of 7.5% (range 1%–50%) of the cyst wall. All 4 cases were from the scalp and treated with local excision. No recurrence was identified with a median follow-up period of 1.5 years (range 1–12 years). The study concluded that sweat duct differentiation in trichilemmal cysts is rare but likely under recognized, and suggested it represents a type of divergent cellular differentiation within a clonal neoplasm rather than a retention cyst or hybrid cyst.