Forty-five patients with aneurysms of the anterior cerebral artery distal to the 
anterior communicating artery were operated on by a direct approach method in 
the years 1960-1973. The incidence of aneurysms in this location was 4.8% of the 
total 1,000 aneurysms. It is of upmost importance in the treatment of aneurysms 
to insure the parent artery for the purpose of temporary occlusion. This makes 
it easier and safer to approach the aneurysmal neck and to handle possible 
premature aneurysmal rupture. From this technical standpoint, the aneurysms in 
this location were classified into two types, ascending and horizontal. 
Aneurysms of the pericallosal artery between the origin of the anterior 
communicating artery and the knee of the corpus callosum were designated as the 
aneurysms of the ascending portion, whereas the aneurysms of the pericallosal 
artery from the knee of the corpus callosum and beyond were designated as the 
aneurysms of the horizontal portion. Depending on the location of the aneurysm, 
craniotomy was performed at one of two different sites. For aneurysms of the 
ascending portion, bifrontal craniotomy was determined and applied as the safest 
approach. A small parasagittal craniotomy was determined to be sufficient for 
aneurysms of the horizontal portion. Although the total operative mortality was 
4 of 45 cases (9.0%), no mortalities nor morbidities occurred in the last 12 
cases since 1972, when the sites of craniotomies were differenciated.