Aims: Saccular aneurysms are commonly located on the bifurcation of the middle cerebral artery. This place is the bifurcation of the temporal and frontal branches arising from the main trunk.

Material and Methods: The M1-M2 junction of the middle cerebral artery may have prominent angulations in the cases with middle cerebral artery aneurysms. The reason of these angulations is the attachment of the aneurysm dome to the arachnoid mater and/or other vascular structures. The attachment of the aneurysm dome to the arachnoid mater around the Sylvian cistern may change the course of the branches originating from a point after the aneurysm dome.

Results: These changes show that the progression of aneurysm dome is a dynamic process. During this process the dome of the aneurysm may continue growing and attach to the surrounding structures. During the surgical treatment of these cases, the dissection of the arachnoid mater over the Sylvian cistern should be done carefully.

Conclusion: The dissection process should be continued until aneurysm dome is completely dissected,and mobilized. If this process could not be achieved, then the blood flow of already distortional vessel may be negatively affected.

Keywords: Middle cerebral artery, aneurysm, aneurysm dome, Sylvian cistern