A RARE CASE OF SIXTH CRANIAL NERVE PALSY CASE REPORT

A 14 year old male patient presented with complaints of double vision which was more on right gaze, of 4 days duration and insidious onset. There was no systemic illness. There was no history of head injury or ocular trauma. Ocular examination showed right face turn and right exotropia that was more in dextroversion. Anterior segment of both eyes were within normal limits. Extra ocular movements showed abduction restriction (-3) in Right Eye (fig 1). Left Eye showed n o r m a l e x t ra o c u l a r m o v e m e n t s . F u n d u s examinations of both eyes were within normal limits. Best corrected visual acuity was 66 in both eyes. Diplopia charting (fig2) showed maximal horizontal separation of uncrossed images on dextroversion. Hess charting (fig 3) showed RIGHT LATERAL RECTUS palsy suggestive of right abducent nerve palsy. Colour vision and visual fields were normal. Examinations of other cranial nerves were within normal limits. Higher cerebral and cerebellar functions were normal. Blood investigations and blood pressure were within normal limits. So ischemia and inflammation were ruled out. Hence MRI Brain (plain and contrast) with MR spectroscopy was done. It showed low signals in T2W and bright signals in T2W FLAIR involving medullary vermian, measuring 1.6 x 1.6 cms (fig 4 6) . Posterior fossa showed normal cerebellum. There was no midline shift. Thalamus, basal ganglia and internal capsules were normal. MR Spectroscopy (fig 5) showed elevated choline and reduction of N-acetyl aspartate (NAA) which was suggestive of cerebellar vermian neoplasm more likely to be primitive neuroectodermal tumour (PNET) Medulloblastoma. Patient was referred to neurosurgery for further management. Neurosurgeons advised palliative treatment and observation. MRI Brain repeated after three months showed no increase in size of the tumour. No surgical intervention was advised as the tumour was small and non progressive.