Osseous Metaplasia and Mature Bone Formation With Extramedullary Hematopoiesis in Trichilemmal Cyst

The study reviewed 88 cases of trichilemmal cysts (TCs) from Bellaria Hospital, identifying 3 cases (3.4%) of ossifying TCs, which were associated with cyst wall rupture and lacked cartilaginous precursors, suggesting a membranous ossification process. These cases were found predominantly on the scalp and presented as red, keratotic nodules. One case uniquely exhibited extramedullary hematopoiesis (EMH), a finding not previously reported in ossifying TCs. The study concluded that ossification in TCs might be more common than previously thought, often linked to cyst wall rupture and possibly involving dystrophic calcification.