The Studies Of The Microsurgical Anatomy Of The Cerebellopontine Angle Associated With The Surgical Management Of Acoustic Neuroma

The relationships among the anerior inferior cerebellar artery, the facialand vestibulocochlear nerve; the labyrinth, the endolymphatic sac and thelandmarks of the posterior wall of the petrous pyramid were studies using *10magnification in 40 cerebellopontine angles(CPAs) from 20 adult cadavers. Thefacial nerve, whose entire course from the brain stem to the entrance of themeatus is 14.58±4.38 (10.52──19.54) mm long,arises in the pontomedullarysulcus 1.98 ±0.099 (1.03──4.46) mm anterior to the point at which thevestibulocochlear nerve join the brain stem at the lateral end of the sulcus,8.15±2.18 (4.54──14.26) mm above the junction of the IX nerve with themedulla. The nervus intermedius is divisible into three parts: (l). A prosimalsegmen that adhere closely to the acoustic nerve, (2) an intennediate segmentlies free between the acoustic nerve and the ot root of the facial nerve,and(3) the distal segment join the motor root of the facial nerve, whose lengthen are6.48 ±4.2l (0──18.85 ) mm, 9.68 ±4.55 (0.85──18.95 ) mm, 5.73 ±2.78(1.4──16.06) mm respectively. In 40 CPAs, there were one rootlet of thenervus intermidus in 22CPAs, tWo in 13 and three in 5 CPAs.The AlCA maiuly originated from the basilar artery as a single (36CPAs90%), duplicate (4 CPAs 10%), from the vertebral artery common with thePICA 3 CPAs (7.5%). The nerve-related arterial trunks were divided into threesegments based on their relationship to the nerves and the meatus: the premeatal,meatal, the postmeatal segments. In relation to the nerves, the premeatalsegment was most commonly anteroinferior, the meatal segment and thepotmeatal segment was inferior. The AICA gave rise to internal auditorywarteries in 39(97.5%)CPAs, recurrent perforating arteries in 36(90%), andsubarcuate arteries in 18 CPAs(45%). There were one to four IAA, zero to threeRPA, and zero to one SA. Drilling of the posterior pyramidal wall may proceedrather safely at a minimum depth of 2.0mm in an area 1 .242cm anterior and0.342cm inferior to the petrosigmoid intersection and petrous ridge, respectvely.It is possible to identify a triangle on the posterior pyramid where certaindrilling guldelines may be given. The apex of this triangle is the petrosigmoidintheection and its base is a line drawn from the most superficial part of thecommon crus to the ampulla of the posterior semicircular canal. the mean depthof the drilling is 0.359l l0.2730cm in itS PO8t6rior POrtion, 0.3087i0.l lcm inity anterior part, and 0.3542l0.26l7cm betwen thOse tWO areas.On the average, the endlymphaic sac was found to be l .3857 t0. l733cmPOSteroSUperior to the XI nerve in thejugular fOramen, l.l685t0.l435cmPOsterior tO the intemal auditOry meatus, and in frOnt of the petr-sigInoidintersection at a POint l .6703 l 0.3509cm, 0. l637i 0.2849cm below the Petrousridge. These anatomy study will help the neuroswneon tO correctly localize thefacial and cochlear nerve and to master the general relationships among thelabghnth. the endolyInPhatic sac and those landInch, resulhng low moraiityand more higher anatondc and hatiOnal Protection of the faCial and cochIearnerve.