Surgical approaches to trigonal arteriovenous malformations.

Only about 5% of intracranial arteriovenous malformations (AVM's) are located predominantly within the ventricular system. Between July, 1981, and February, 1986, 15 patients were treated at the authors' institution for AVM's within the ventricular trigone. The mean age of this patient population was 24 years, and two-thirds were female. Intracranial hemorrhage was by far the most frequent presenting symptom and intraventricular hemorrhage occurred in 11 cases, with multiple episodes being documented in five. Arterial supply of the malformations was quite uniform, with the lateral posterior choroidal or posterior temporal branch of the posterior cerebral artery (PCA) being the most frequent source. Venous drainage was similarly stereotypic, with predominant outflow into the galenic system in all but one patient. An interhemispheric surgical approach was used in eight patients, a middle or inferior temporal gyrus incision was performed in six, and a subtemporal route was chosen in a single patient. Operative results suggest that these lesions can be removed with reasonable safety. An interhemispheric approach is recommended if the nidus projects medially from the trigone and is observed medial to the P2-P3 junction of the PCA on angiography. A middle temporal gyrus approach is suggested if the nidus is lateral to the P2-P3 junction, even when the lesion is located in the dominant hemisphere. A subtemporal approach should be reserved for inferiorly projecting AVM's with cortical representation on the fusiform or parahippocampal gyrus in the nondominant hemisphere.