1. 14 Anterior inferior cerebellar artery(AICA) and labyrinth artery, petrosal vein , cranial nerve V, VII, VIII, through the Cerebellopontine cistern.

2. The fossil mammalian groups morganucodonts, triconodonts and multituberculates possess a reduced Alisphenoid and a large anterior process of the petrosal

3. The posterior part of each Alisphenoid forms a triangular process which fits into the angle between the squamosal and the petrosal

4. Neuro angiography and interventions: including aneurysm Coilings, AVM embolizations, carotid stenting, WADA testing for seizures/epilepsy, petrosal sinus sampling for Cushing's Disease, Gammaknife mapping (Cherry Hill location) Possible complications

5. This study confirms that despite a significant extra time needed for proper achievement, the combined petrosal approach is a valuable conservative approach when the petroclival area, ventral brain stem and Basilary trunk are targeted

6. We report six cases of segmental agenesis of the internal carotid a. discovered in adult patients: one case of cervical segmental agenesis (no. 1), one case of cervical and petrosal segmental agenesis (no. 2), two cases of vertical cavernous segmental agenesis (nos. 3 and 4) and two cases of distal segmental agenesis, one unilateral (no. 5) and the other bilateral (no. 6).