Delayed cerebral pseudoaneurysm following surgical and combined-modality therapy for glioblastoma multiforme: illustrative case.

backgroundPost-radiation therapy and chemotherapy cerebral pseudoaneurysms are rare entities. Within previous tumor treatment areas on nonvascular imaging, they are potentially confused as recurrent tumor. OBSERVATIONS: A 61-year-old man was a long-term survivor of glioblastoma multiforme whose treatment consisted of open biopsy followed by radiotherapy to 60 Gy and systemic carmustine. On surveillance imaging, enlargement of a posttreatment cyst and new enhancing lateral "mural nodule" was first noticed approximately 16 years after initial treatment. Over 12 months, both continued to enlarge. Initially referred to as recurrence, subsequent angiography showed the mural nodule to be an unruptured distal middle cerebral artery pseudoaneurysm within the previous tumor bed. The patient underwent repeat craniotomy for clipping of the aneurysm and biopsy of the cyst wall, which was negative for malignancy. LESSONS: Delayed pseudoaneurysms following radiation therapy and chemotherapy for malignant brain tumors are rare but have been previously reported. Their appearance on cross-sectional imaging can mimic recurrence, and they should be kept in the differential of new, circumscribed enhancement within such treatment areas.