Osteosarcoma of the skull base presenting as a petrocavernous pseudoaneurysm and masquerading as an intracranial abscess: illustrative case

BACKGROUND: Telangiectatic osteosarcoma (TOS) is a rare and aggressive high-grade malignant neoplasm composed of blood-filled or empty cystic spaces resembling aneurysmal bone cysts. Uncommonly, TOSs can occur in the skull base. OBSERVATIONS: The authors present a case of a TOS that presented as a petrocavernous carotid pseudoaneurysm and then masqueraded as an intracranial abscess. The prognosis for TOSs with intracranial involvement is typically unfavorable and inversely related to the degree of intracranial involvement. LESSONS: Skull-based malignancies should be part of the differential diagnosis for a rapidly progressing lesion. Recovery of polymicrobial organisms during endoscopic sinus surgery should prompt reconsideration of the differential diagnosis. Postinflammatory changes from endovascular coiling have been described and can confound imaging and clinical findings.