Hyperperfusion syndrome after neck clipping of a ruptured aneurysm on a dolichoectatic middle cerebral artery.

A 40-year-old female presented with sudden onset of severe headache and vomiting due to subarachnoid hemorrhage. Angiography demonstrated a saccular aneurysm on a dolichoectatic left middle cerebral artery (MCA) and delayed filling of the MCA. Magnetic resonance imaging showed a partially thrombosed giant aneurysm on the dolichoectatic MCA. An intentionally delayed operation was performed, during which the neck of the aneurysm was successfully clipped. The patient exhibited aphasia 48 hours after surgery. Single-photon emission computed tomography revealed hyperperfusion in the territory of the left MCA. The patient's blood pressure was maintained normotensively, and her symptoms gradually improved. She returned to work 1 month after surgery. The saccular aneurysm was formed on the dolichoectatic MCA, presumably due to an abnormal arterial wall and hemodynamic stress. The preoperative hypoperfusion might have been caused not only by the giant aneurysm, but also to some degree by the dolichoectatic MCA. After neck clipping, the increase in blood flow might have caused hyperperfusion.