Microsurgical Anatomy Of The Space Around Internal Acoustic Canal In Posterior Cranial Fossa Via Keyhole Approach And The Clinical Applications

Objective: Microsurgical technique around internal acoustic canal has become increasingly aggressive recently. We observed more detailed microanatomic material by endoscope via suboccipital retrosigmoid approach. It was the figuration basement of operation.Materials and Methods: Thirty adult cadavers head soaked in formalin were studied with microscope , endoscope via suboccipital-retrosigmoid approach. We observed the major structure of this region; measured the distant between star spot and the important operative corridor marks; depicted the angle between the approach and the sagittal plane. Results: (1) The longitudinal incision was 3. 5+0. 5cm long , which superior extremity was star spot. The skull window was located posterolateral to star spot , which is 2. 50. 5cm in diameter. (2) The operative corridor is between the subdura and epiarachnoed space , which was located posterior to petrous bone, anterolateral to cerebella, anterior to flocculus. And the angle between the approach and sagittal plane was 45+2.5 . (3) Although thepathway was narrow , the views of operation field was greater than before, which can reach abduens nerve superiorly, jugular foramen inferiorly.Conclusion:(1) The "keyhole" technique is selected individually depend on conditions of the imaging examination as well as the lesion of the patient. It is a minimally invasive technique and can reduce the operative trauma. (2) The major factors for correctly reaching the lesion is to approach according to certain anatomic marks but not the approaching angle and depth. (3) The approach is in the epiarachnoid space and the arachnoid should be kept intact to protecting brain debri covering the visual field. (4) The marks of road mapping for this approach include star spot, sigmoid sinus, anterior inferior cerebellar artery, trigeminal nerve, superior cerebellar artery, abducent nerve, cranial nerve IX, X, XI, posterior inferior cerebellar artery. (5) It is important the pathway of road mapping for this approach need to be kept in mind , and that master perfectly this technique.