Midline dermoid cyst resulting in frontal bone erosion.

A dermoid cyst is a thin-walled benign tumor formed by the entrapment of ectodermal tissue during embryologic development, resulting in the inclusion of epithelium and adnexal elements within the tumor. Dermoids are not unique to a single anatomic location but are often isolated to the skin and subcutaneous tissue. They may occur intracranially or intra-abdominally, oftentimes associated with the ovary. If presenting as a midline mass of the skull, preoperative imaging with computed tomography and/or magnetic resonance imaging is necessary to evaluate for possible intracranial extension, given the altered embryologic development behind the formation of these cysts. Differential diagnosis of a midline frontonasal mass includes epidermoid or dermoid cyst, encephalocele, glioma, and sinus pericranii. The management of suspected dermoid cysts includes complete surgical excision, which may require a combined intracranial and extracranial approach. We present a 2-year-old boy who presented to our institution with a congenital midline scalp mass separate from the anterior fontanelle with complete underlying bony erosion to the sagittal sinus demonstrated on preoperative imaging, who required early surgical excision and reconstruction of the bony defect.