Progressive thrombosis and involution of a pediatric giant middle cerebral artery pseudoaneurysm following superficial temporal artery-to-middle cerebral artery bypass: illustrative case.

backgroundDirect arterial cerebral bypass is commonly performed as part of the definitive treatment strategy for complex aneurysms. While several reports have demonstrated aneurysm thrombosis after direct bypass alone, this report highlights the successful treatment of pediatric giant pseudoaneurysm with direct bypass, leading to thrombosis without requiring additional steps for aneurysm trapping. OBSERVATIONS: A 13-year-old male presented with vomiting and the worst headache of his life. Imaging revealed a partially thrombosed giant right middle cerebral artery (MCA) pseudoaneurysm and right MCA territory hypoperfusion. Superficial temporal artery-to-MCA (STA-MCA) bypass was performed, with planned endovascular trapping for definitive aneurysm treatment in a few months. Angiography 3 months postoperatively demonstrated nearly complete thrombosis of the pseudoaneurysm and a patent bypass; thus, additional treatment was not needed. At the 2-year follow-up, the patient was doing well with an active age-appropriate lifestyle and no aneurysm recurrence. LESSONS: This is the first case report of successful treatment of a pediatric giant MCA pseudoaneurysm with STA-MCA bypass, obviating the need for additional treatment in a planned stepwise strategy. STA-MCA bypass alone may be an alternative for the treatment of certain complex MCA aneurysms in pediatric patients when standard approaches are not straightforward. https://thejns.org/doi/10.3171/CASE2591.