to preserve all blood vessels passing over the surface of the tumor. Many of the arteries looping over the tumor will supply the brain-stem. The trigeminal nerve and superior pet-rosal vein can usually be identified superiorly. Lintine strips are eased into the plane around the tumor capsule to protect the brainstem. Inferiorly, the lower cranial nerves and posterior inferior cerebellar artery are protected from the tumor. Care must be taken in larger tumors not to over-retract either the neuraxis or the tumor. In such tumors, early attention to CSF drainage helps, but exposure of the tumor margins must be performed in an incremental fashion. The surface of the tumor is diathermied to reduce vascularity during this phase of exposure. The canalicular and anterior aspects of the tumor are left undisturbed at this point.
The tumor surface is then incised and the tumor debulked from within using an ultrasonic aspirator. Care is taken not to perforate the tumor during this maneuver. After debulking the tumor, further exposure of the capsule can be made taking care to protect the brainstem structures. Sequential exposure and debulking can then be performed. The brainstem end of the facial nerve requires exposure. Essential landmarks are the choroid plexus of the Foramen of Luschka, the line of the glossopha-ryngeal nerve and the pontomedullary sulcus. Once the facial nerve has been identified the cochlear and vestibular nerves are sacrificed at the brainstem end. The tumor is then rolled laterally towards the internal auditory canal. The position of the facial nerve is carefully observed. The tumor is then dissected from the facial nerve using microscissors under a modestly irrigated operating field. The tumor may be adherent to the dural margins of the porus acousticus. The ring of dura enveloping the tumor needs to be opened at both shoulders of the tumor. The facial nerve is often very thin and splayed at this point. At times, the facial nerve can be followed from lateral to medial, gently retracting the tumor into the CPA whilst dissecting the tumor from the nerve. Eventually, the tumor will be removed. After ensuring resection is complete, hemostasis is secured, using irrigation and application of a monolayer of oxidized cellulose patches to the brainstem.
The principal objective during closure of the wound is to ensure that CSF leakage cannot occur. The eustachian tube and middle ear are sealed with small pieces of fat and fibrin glue (Tisseel, Immuno IG, Vienna, Austria). A patch of fascia lata (2 x 2.5 cm), secured with fibrin glue, is then placed over the drilled surface of the petrous bone to cover the middle ear. Three finger-sized strips of fat are then placed just into the CPA and anchored superficially with fibrin glue. The mastoid air cells are sealed with bone wax. The pericranium is then closed. The galea, reinforced with a fascia lata patch, is sutured. Finally, the scalp is closed in two layers.
To minimize the risk of CSF leak, we recommend daily lumbar punctures, reducing the CSF pressure to +5 cm on the first three postoperative days. These are performed in preference to leaving a lumbar drain in situ to encourage early ambulation. The post-operative hospital stay is variable, but is around 5 or 6 days in healthy ambulant patients.
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