Anatomical Study On The Cerebellopontine Angle(CPA) And Petroclival Area By Retrosinmoid Sinus Approach And The Application On The Resection Of Macrocholesteatoma Of The Transmediposterior Cranial Fossa

Background:The labyrinth approach and suboccipital approach have been used to treat the diseases of Cerebellopontine Angle(CPA) ever since. The defect of labyrinth approach is small exposed area and damaging hearing. The insufficient of suboccipital approach is longer distance,more damage,more restraction to cerebullum and brain stem and sometimes sacrificing the part of cerebullum. With the development of medical technique and radiological methods,the retrosigmoid sinus approach(RSSA) has been one of otoneurosurgerical approach and superiority over other approach of treatment the diseases in CPA. Since Jannetta first reported the operation in hemifacial spasm and trigeminal neugalgia by RSSA, this approach had been used to resect the tumour of CPA and as to resect the macrocholesteatoma of the transmediposterior cranial fossa. But it is not reported that the related anatomical study on the cerebellopontine Angle(CPA) and petroclival area.Objective:To observe and survey the anatomical structures in CPA and petroclival area by the retrosigmoid sinus approach. And to study its feasibility , operating methods, application and announcements in resecting the macrocholesteatoma of the transmediposterior cranial fossa. METHOD:It was observed that the design of flap, the structure of nerve and vasculature in CPA and petroclival area and tentorium cerebelli foramen on 3 cadaver heads. The distance from the "D" points of the posterior edge of the sigmoideus sinus to every observed points was measured. In clinic, there have been used to resect the macrocholesteatoma of the transmediposteriorcranial fossa in 8 patients by this approach. Its operating methods,outcome and complication were introduced.RESULTS:The design of flap in this approach is simple and convenient. The correct design will help to fix the bony window. The front-rear diameter of tentorium cerebelli foramen average 4.85cm,the right-left diameter at the intersection of superior edge of petrous bone 3.45cm.The distance from the "D" point of the posterior edge of the the sigmoideus sinus to the posterior clinoid process, intersection of the oculomtor nerve acrossing the superior edge of petrous bone, the exit zone of abducent nerve, the point of abducent nerve entry cerebral dura mater,the entry zone trigmeminal nerve, the posterior edge of trigmeminal impression, the exit zone of facial nerve, the entry zone of vestibulocochlear nerve, the posterior edge of internal acoustic pore, the entry zone of glossopharyngeal-vagus-accessory nerve and the the posterior edge of jugular foramen wre 6.37 cm, 5.92 cm, 4.88 cm, 5.09 cm, 4.31 cm, 4.51 cm, 3.83 cm, 3.70 cm, 3.25 cm, 3.88 cm, 3.22 cm respectively. In the clinic, the macrocholesteatoma of the transmediposterior cranial fossa were completely resected at single-stage by the retrosigmoid sinus approach in 8 patients. After all patients followed up for 2-10 years, all symptoms had vanished. The complications were chemical meningitis in 3 cases and blepharoptosis in 1 patients. They were cured completely in follow-up.CONCLUSION: The operation by retrosigmoid sinus approach is a small incision between the labyrinth approach and suboccipital approach. Its advantages were less damage, shorter distance and more exposed area. Because the pathological feature of cholesteatoma is more tender quality and intact membrane, the macrocholesteatoma of the transmediposterior cranial fossa could been completely resected at single-stage by this approach.