Surgical management of a ruptured cirsoid aneurysm: illustrative case.

backgroundCirsoid aneurysms are rare arteriovenous fistulas involving direct connections between scalp arteries and draining veins, often located within the periosteal or temporal fascia, or beneath the galea. First described by Brecht in 1833, these lesions may be congenital or posttraumatic and can occasionally be associated with intracranial vascular malformations. OBSERVATIONS: A 69-year-old woman with thrombocytopenia developed a large cirsoid aneurysm in the right parieto-occipital subcutaneous region following head trauma. The lesion evolved into a soft tissue hematoma, eventually leading to a spontaneous cutaneous fistula with active, profuse bleeding. An endovascular embolization attempt failed due to complex vascular architecture. Emergency surgical intervention was performed for hematoma evacuation and complete resection of the vascular malformation. LESSONS: This case is unique in combining several high-risk factors rarely reported together: an acutely ruptured cirsoid aneurysm, severe thrombocytopenia, and failed endovascular embolization due to prohibitive vessel tortuosity. A successful outcome was achieved through rapid multidisciplinary coordination-integrating neurosurgical expertise for definitive nidus excision, hematological optimization, and reconstructive planning to preserve scalp integrity. https://thejns.org/doi/10.3171/CASE25508.