Anatomical Study Of The Neurovascular Complex In The Cerebellopontine Angle Region

Objective: In order to afford anatomical material for clinical microvascular decompression, improve operative efficiency, decrease complications, the anatomical structures of the neurovascular complex and some important inside/outside bone structures in the cerebellopontine angle (CPA) region was investigated.Methods: (1)20 adult cadaveric heads fixed in 10% formalin and perfused with red latex in artery and blue latex in vein were used for this study. Cerebrum was cut from the midbrain , the dura covering cerebellum was removed, and the trans-suboccipital retrosigmoid approach to the CPA region was simulated. All stages of the dissection were performed gradually, observed, photographed. (2)Some important bone strutures of the inside and outside of posterior cranial fossa were observed and measured in 20 cadaveric skull specimens of adults which the upper bones were removed.Results: (1)The upper neurovascular complex included trochlear nerve,trigeminal nerve and the superior cerebellar artery(SCA), the anteroinferior cerebellar artery(AICA), the superior petrosal vein, the superior petrosal sinus, and midbrain cerebelomesencephalic fissure, et al. Oculomotor nerve constantly penetrated through between the original parts of the posterior cerebral artery (PCA) and SCA. 80% SCA was single, and often formed loop which directed downward during the course of its journey .The SCA which compressed trigeminal nerve had always loop, the upper side of the trigeminal nerve entering/exiting zone of brainstem was sometimes compressed by the trunk loop and the beginning part of the branch of the SCA. 60% the superior petrosal vein had two branches, 40% of the vein compressed the trigeminal nerve . Trigeminal nerve was probably compressed by a vessel more than one time, what's more, one trigeminal nerve might be compressed by many vessels, and trigeminal nerves of both sides could be compressed in one case. The middle neurovascular complex included abducens , facial , vestibulocochlear nerve, AICA, the posteroinferior cerebellar artery(PICA),and so on. The facial nerve was in front of the vestibulocochlear nerve, and the nerve exiting zone of brainstem situated anteroinferior in the cerebellopontine fissure. 92.50% AICA originated from basilar artery(BA). 57.50% AICA went throughⅦ,Ⅷcranial nerves, 42.50% AICA passed on the surfaces of them. AICA often folded and entered the internal acoustic meatus with a labyrinthine branch. Facial and vestibulocochlear nerves was compressed by 14.28% SCA. The lower neurovascular complex mainly included medulla oblongata, glossopharyngeal, vagus , accessory and hypoglossal nerve, PICA, vertebral artery(VA). PICA is the biggest branch of VA, and 92.50% PICA originated from VA, 10.26% PICA passed over glossopharyngeal nerve, 2.56% PICA ran between the glossopharyngeal and vagus nerves, 66.66%PICA went through spinal accessory nerve, 10.26% PICA lied behind them. 10.26% PICA didn't touch with them, the rest compressed them, glossopharyngeal nerve was compressed by 12.81% PICA. 85% VA situated in front of hypoglossal nerve, and compressed it. In all cases, the VA and BA which compressed cranial nerves were not observed.(2)The point of STP , jugular foramen, internal acoustic pore were important bone landmarks in the internal posterior cranial fossa. The distance of the point of STP to internal acoustic pore: left 32.99±2.72mm, right 37.84±2.58mm, to jugular foramen: left 35.27±3.25mm, right 34.63±3.25mm. Internal acoustic pore was above the jugular foramen nearly 5mm, and the inter entrance of hypoglossal canal was under the jugular foramen about 20mm, what's more, the three parts were in one line. Petroclival region was ahead of the jugular foramen. Mastoid process was a very important bone landmark in the outer posterior cranial fossa, styloid process was interior-anterior of the process, jugular foramen outside hole was interior of styloid process, and outer entrance of carotid canal was anterior of jugular foramen outside hole. Hypoglossal canal and occipital condyle were interior of the foramen.Conclusions: The neurovascular complex in the CPA region was located deeply and had a complicated structure, which was near brainstem, cerebellum and other important organs. A complete structural dissection of this region could benefit the integrity of nerves and improve the success of operation. Trigeminal neuralgia, hemifacial spasm, glossopharyngeal neuralgia and other cranial nerval diseases might not be caused by vascular compression simply, perhaps there were many other factors, or all these factors together led to symptoms. There might be more than one compressive vessel and more than one compressive point and these should not be ignored in operation. The point of STP, internal acoustic pore and jugular foramen were very important landmarks for operative approach in the posterior cranial fossa.