Unruptured distal anterior cerebral artery branch pseudoaneurysm in the setting of intracranial pressure monitor placement: illustrative case.

backgroundIntracranial pressure monitors (IPMs) are commonly placed in patients with severe traumatic brain injury to diagnose and guide treatment for intracranial hypertension. Complications of IPM placement include infection, hemorrhage, and malposition. While rare case reports describe ruptured iatrogenic pseudoaneurysms associated with IPM, the incidence and implications of unruptured pseudoaneurysms are poorly understood. OBSERVATIONS: A 19-year-old female sustained a severe traumatic brain injury, leading to IPM placement. After a prolonged hospital course, delayed noninvasive imaging to characterize potential cerebrovascular injury raised concern for a carotid-cavernous fistula. Digital subtraction angiography (DSA) ruled out this pathology but revealed an unruptured distal right anterior cerebral artery pseudoaneurysm at the site of the previously placed IPM, which was later successfully treated with endovascular embolization after short-interval repeat DSA. LESSONS: While pseudoaneurysm formation is a rarely described complication of ICM placement, they are associated with a high rate of rupture (60%) and, subsequently, high mortality (20%). Thus, a high index of suspicion of potential pseudoaneurysm rupture should be maintained in the setting of a delayed rapid decline in neurological examination or delayed intraparenchymal hemorrhage after IPM placement. Urgent evaluation using CT angiography and/or catheter angiography should be considered in addition to standard noncontrast imaging. https://thejns.org/doi/10.3171/CASE251022.