Abstract
Abstract: :
Purpose: Brain tumors account for 25% of all tumors in childhood, of which posterior fossa tumors are the most common. This study examines the oculomotor and vestibulo–ocular findings in patients treated surgically for these tumors. Methods: 8 patients (mean age = 10 years) with posterior fossa tumors (5 with medulloblastoma, 2 with cerebellar astrocytoma, and 1 with ependymoma) were studied following surgery. Patients had quantitative eye movement recordings using binocular video–oculography to evaluate gaze holding, conjugate eye movements (saccades, smooth pursuit, full field OKN, and vertical axis VOR in the dark), and accommodative vergence. All patients had pre– and post–operative MRIs. Results: All patients had a spontaneous nystagmus in the dark (mean = 5°/s), 4 were purely horizontal. 4 patients had a gaze holding nystagmus with 15°. eccentric fixations in the light. Smooth pursuit gains during horizontal tracking (±10° sinusoids, peak velocity of 10, 20 and 30 deg/s) were < 0.5 with numerous saccadic intrusions in 7 of 8 patients. Saccades were uniformly dysmetric, and typically hypermetric. Average horizontal OKN gains were 0.39, 0.28, and 0.24 for a 15, 30 and 45°/s constant velocity stimulus (0.1 cycles/°). Vertical OKN was asymmetric, with upward directed stimuli eliciting lower gains than downward directed stimuli at each stimulus velocity (0.36 vs. 0.55, 0.24 vs. 0.30, 0.06 vs. 0.20 at 15, 30 and 45°/s respectively). Sinusoidal vertical axis VOR gain ranged from 0.7 to 1.2 at 0.3 Hz. Accommodative vergence was elicited with a Snellen target that was advanced along the midline. Vergence gains were normal in all patients tested. MRI confirmed that the patients had tumors that were fully resected. The resections primarily compromised rostral midline cerebellar structures. Conclusions: Patients display a wide range of oculomotor and vestibulo–ocular following resection of posterior fossa tumors . Severity of the abnormalities is correlated with the involvement of known oculomotor regions within the cerebellum. A prospective study has been initiated to quantify eye movements pre– and post–operatively in such patients.
Keywords: eye movements • oncology • ocular motor control