前大脳動脈水平部 (A1) 脳動脈瘤の検討

Abstract

Proximal anterior cerebral artery aneurysms (A1 An) are rare and occupy 0.88-4% of all cerebral aneurysms. They are characterized by both vascular anomalies and high incidences of multiplicity. We had 288 patients, including some with multiple surgeries, resulting in a total of 339 operations in our hospital from November 1991 through November 1996. Of the 339 operations, 6 cases (1.8%) were of the A1 An type. We outline the characteristics of A1 An, the diagnoses and operations.Patients were 60 years old on average. Two cases suffered from subarachnoid hemorrhage and the remaining 4 had unruptured aneurysms. All A1 An were saccular and occurred at the origin of perforators. The sizes of 6 cases were 3.0mm on average. In 5 of 6 cases, the location of the A1 An was within one-third of the length of Al on the proximal side. Vascular anomaly existed in none of our cases, but in 1 case multiple aneurysms existed. All cases were approached via ipsilateral frontotemporosphenoidal craniotomy. To avoid excess compression of the frontal base, we set up the patient's head in the vertex down position, taking care to avoid kinking of perforators of Al at the clipping.The size of ruptured A1 An in our cases were 3.4mm and 3.5mm, which is smaller than the average 8.2mm size of aneurysms in other regions. Therefore, it can be said that one of the characteristics of A1 An is the high risk of the rupture in spite of its small size.When we diagnose A1 An, it is important to understand its characteristics. We should not miss the vascular anomaly and the other anuerysms. It is also important to avoid compression of the frontal base and kinking of perforators of Al at the operation.Finally we suggest that operation of A1 An should be positively considered unless it is of belowaverage size as there is a high risk of rupture in such cases.