Fig. 3.

Schematic illustrations showing the relationship between the CMF and the tonsillomedullary segment of the PICA. An aneurysm of the proximal portion of the PICA is located in front of the lower cranial nerves. (A, B) These illustrations show typical type of the caudal loop of the tonsillomedullary segment of the PICA. The caudal loop is located at the lower level of the caudal tip of the tonsil. (A) The OA-PICA bypass was performed without using the trans-CMF approach. (B) An aneurysm is trapped using titanium clips. The transcondylarfossa approach was suitable for trapping of the aneurysm. (C, D) These illustrations show high position of the caudal loop of the PICA. (C) The caudal loop of the tonsillomedullary segment of the PICA, which is located in the upper part of the CMF without a large caudal loop, was exposed after opening the CMF. (D) The OA-PICA bypass and trapping of the aneurysm were performed using the trans-CMF approach.