Heterotopic Intracranial Skin Presenting as Chronic Draining Sinus After Remote Craniotomy

Background Craniotomies for trauma are associated with a significant risk of wound complications. We report a case in which a chronic nonhealing draining sinus was caused by an ectopic epidermal lining deep to the craniotomy bone flap, adherent to the underlying dura. Case Description A 61-year-old man was examined for a 3-year-old, nonhealing scalp wound resulting after a traumatic brain injury. His initial surgery consisted of an intracranial hematoma evacuation through a temporoparietal craniotomy; this was complicated by wound dehiscence and a chronic sinus draining clear fluid that did not resolve with antimicrobial therapy. Intraoperatively, a layer of hair-bearing skin adherent to the dura was found deep to the entirety of the previous bone flap. There was no dura tear or overt cerebrospinal fluid leak. This necessitated removal of the skin over the dura as well as the overlying bone flap. The resultant defect was reconstructed with a titanium mesh and hydroxyapatite cranioplasty, with a scalp rotation flap for coverage of the cutaneous defect. Pathology confirmed skin with intact adnexal structures. Conclusion This case demonstrates that it is possible for hair-bearing skin to grow directly on dura, deep to an intact craniotomy bone flap. With a chronic draining sinus in the absence of computed tomography and magnetic resonance imaging findings, this should be part of the differential diagnosis.