Epidermal Inclusion Cysts With Cranial Bony Erosion Mimicking Dermoid Cysts: A Diagnostic Pitfall - A Series of 4 Patients.

Craniofacial cystic lesions with underlying bony erosion are classically associated with dermoid cysts, while such involvement by epidermal inclusion cysts (EICs) is considered rare. The authors retrospectively reviewed 4 patients (ages 1-31 y) who underwent excision of craniofacial cysts with bony erosion. All lesions occupied deep tissue planes-including the subtemporoparietal fascia, submuscular, or subgaleal spaces-with firm adhesions to the underlying skeleton. Although preoperative imaging suggested dermoid cysts in all cases, final histopathology confirmed EIC. This series demonstrates that cranial bony erosion is not pathognomonic for dermoid cysts; EICs in deep enclosed planes can induce bony remodeling through chronic mechanical pressure. EIC should be included in the differential diagnosis of any craniofacial cystic lesion with bony erosion, and mandatory histopathological examination remains essential for definitive diagnosis.