Traumatic pseudoaneurysm of a distal middle cerebral artery branch with findings suggestive of an interdural location: illustrative case.

backgroundTraumatic intracranial pseudoaneurysms are rare, and those located between the dural layers (interdural space) are exceptionally uncommon. The authors describe a delayed pseudoaneurysm arising from a distal middle cerebral artery branch, with multimodal findings most consistent with an interdural location. OBSERVATIONS: A 56-year-old man sustained a fall-related head injury with right frontal contusion, frontal bone fracture, and superior orbital wall fractures. Initial 3D CT angiography (3D-CTA) showed no vascular abnormality; however, follow-up 3D-CTA on day 20 revealed a de novo 4-mm pseudoaneurysm of the lateral orbitofrontal artery (LOFA) adjacent to the fracture. During surgical trapping, the parent LOFA was observed to enter and exit the dural layer proximally and distally, respectively, and the lesion was resected en bloc with the adherent dura. Histopathological analysis confirmed the lesion as a pseudoaneurysm, and the interdural location was inferred from the integration of intraoperative anatomical findings and gross specimen continuity with the dura. LESSONS: This case suggests that traumatic pseudoaneurysms from intracranial arteries may rarely develop in an interdural location and may present with a delayed onset. Repeat vascular imaging may be considered for selected high-risk fractures anatomically adjacent to intracranial arterial pathways, even when the initial CTA findings are negative. https://thejns.org/doi/10.3171/CASE26393.