Evaluation of the retrosigmoid approach for fourth nerve neuroma excision

ABSTRACT

Schwannomas originating from the trochlear nerve without neurofibromatosis are extremely rare. Thirty four cases have previously been reported in the literature, and only 25 cases were pathologically diagnosed, five of them had a large cystic component and a smaller solid portion. Complex skull base approaches have been usually applied for their removal. The aim was to report two cases of trochlear schwannomas operated in the international neuroscience institute in Hannover, Germany. This is a retrospective report on two cases of trochlear schwannomas operated in the international neuroscience institute in Hannover, Germany, first case was a 62 years old female patient who presented to us complaining of, decreased hearing on the right ear and decreased sensation over the right side of the face, with vertigo gait instability for more than one year. The magentic resonance imaging examination revealed an intensely enhancing well circumscribed 3 cm large extra axial lesion, compressing the brain stem at the lower midbrain and upper pons level. Second case was a 49 years old female with long history of trigeminal neuralgia attacks, with a failed medical treatment for such problem. Lately one year ago she started to complain of hearing difficulty on the left ear, with decreased of the trigeminal pain with decreased sensation on the left side of the face which was attributed to the trigeminal ganglion block done one year ago Magnetic resonance imaging revealed a 2.5 cm left sided extra axial lesion compressing the brain stem at the lower midbrain and upper pontine level. Total resection was performed via a retrosigmoid craniotomy appraoach. In the two cases the trochlear nerve was fanned out and unified with the tumor. The tumor was diagnosed as a schwannoma. The Retrosigmoid approach is a safe surgical approach for removal of the trochlear schwannomas in comparison to the other surgical approaches. Total tumor removal without additional morbidity can be achieved through that approach, especially for lesions in the middle incisural space can be safely removed via the retrosigmoid approach. The gradual development of trochlear nerve palsy is well compensated for by other extraocular muscles. Normal vision is not impaired or returns soon postoperatively