Cranial Nerves

The trigeminal nerve, comprising a small motor root and a larger sensory root, arises from the lateral aspect of the rostral pons. It courses, in an anterior, lateral and slightly superior direction, towards the porus trigeminus at the entrance to Meckel's cave. The IX, X and XI nerves arise in the longitudinal sulcus lateral to the olive. They course through the inferior cerebellopontine cistern to the jugular foramen. The facial nerve arises 2 or 3 mm superior to the rostral rootlets of the glossopharyngeal nerve, from the lateral aspect of the pontomedullary sulcus. The VIII nerve leaves the pontomedullary sulcus about 1 mm lateral to the facial nerve. The nervus intermedius is usually closely applied to the VIII nerve at this point. The VII and VIII nerves then become apposed as they course toward the porus acousticus (internal auditory meatus). The presence of transverse and vertical (Bill's bar) crests of bone within the internal auditory canal enable the surgeon to identify with certainty the location of the facial nerve and the subdivisions of the vestibulo-cochlear nerve. The superior and inferior vestibular nerves occupy the postero-superior and postero-inferior quadrants of the canal, respectively. The antero-superior quadrant is occupied by the facial nerve and nervus intermedius, whilst the cochlear nerve lies antero-inferiorly. Since most acoustic neuromas arise from one of the vestibular nerves, the cochlear and facial nerves are usually displaced anteriorly.

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