Retrosigmoid Approach to Ventrolateral Pontine AVM

Abstract

There are a number of different surgical approaches to pontine lesions, such as the anterior transpetrosal (Kawase's) approach, lateral (presigmoid) approach, and rhomboid fossa approach. The anterior transpetrosal approach is only suitable for exophytic lesions and the rhomboid fossa approach is problematic because of the possible damage to neural structures in its path. Yoshitusugu Oiwa et al reported on the removal of a pontine lesion through the presigmoid approach in which the lateral surface of the pons is approached through a small window without any additional neurologic deficit. The authors report on the successful removal of a pontine AVM (intra-axial) situated on the rostral part of the pons (lateral pontine surface) between the CN V and VII-VIII complex through a conventional retrosigmoid approach using a small lateral incision. The patient complained of sudden-onset headache and right-sided hemiparesis; brain CT showed hematoma on the left ventrolateral pons. There was sudden decreased consciousness on the fifth day of admission and follow-up showed rebleeding on the site. After transfemoral cerebral angiography and brain MRI, the hematoma and lesion were removed via a left-sided retrosigmoid approach. The lesion was confirmed as a pontine AVM. The patient recovered consciousness on the fifth postoperative day and showed signs of dense right-sided hemiparesis, diplopia, central-type facial palsy (left), and hearing loss. Exams at 15 months postoperatively showed full recovery of diplopia with near normal recovery of hemiparesis and facial palsy, but the hearing deficit was not improved. The important neural structures of the pons are (1) the corticospinal tract in the ventral pons, (2) reticular formation in the central pons, and (3) most of the nucleus in the dorsal part of the pons (rhomboid fossa). The middle cerebellar peduncle is in the lateral pons but a small incision on the peduncle results in only transient aggravation of cerebellar ataxia, so a surgical approach through the lateral pontine surface is feasible, which makes the conventional retrosigmoid approach a excellent choice in that area.