Expansile Anterior Cranial Fossa Intradiploic Epidermoid Cyst: An Endoscopic Endonasal Approach to Resection

Introduction: Epidermoid cysts are uncommon lesions representing ~1% of all intracranial tumors. They are benign, slow-growing lesions with low potential for malignant transformation. Their pathogenesis is derived from ectopic growth of epidermoid tissue in the setting of congenital migration abnormality or post-traumatic seeding. In the intracranial cavity, they are most commonly located at the cerebellopontine angle and parasellar region, and are rarely found in the frontoethmoidal region. Here we report a giant intradiploic frontal epidermoid with resultant tension pneumocephalus, resected through an endonasal approach.

Case Description A 38 year-old Hispanic male presented with right eye pain and swelling. He had one similar episode three months prior that resolved with antibiotics and antihistamines. On examination, he was neurologically intact with right-sided peri-orbital crepitus and maxillary and frontal sinus tenderness bilaterally. Maxillofacial CT was obtained which showed an expansile, frontal lobe lesion with destruction of the frontal sinus and frontal bone as well as pneumocephalus extending into the right orbit. These finding were concerning for intracranial abscess. MRI of the brain was obtained and showed an extra-axial, heterogeneous mass with a large amount of interdigitating gas, concerning for a fungal infection such as Aspergilloma. He underwent an endonasal endoscopic approach to the anterior skull base for exploration of the lesion. Surgical pathology was consistent with epidermoid cyst. He was transferred out of the ICU on post-operative day 1 and was discharged home on post-operative day 4 without neurologic deficit.

Discussion: Surgical resection, including removal of the cyst wall, has long been accepted as definitive treatment for symptomatic epidermoid cysts. Clinical decision making regarding open versus endoscopic approach to frontal sinus and skullbase lesions must consider anterior-posterior and medial-lateral intracranial extension. Here we highlight a case in which posterior extension along the anterior cranial fossa and the expansile nature of this epidermoid cyst facilitated endoscopic, endonasal access to the lesion.