Test Your Knowledge - Optokinetic nystagmus with a parietal lesion
Abnormal OKN, Jerk Nystagmus
Tony Brune, DO, Departments of Neurology, The Johns Hopkins School of Medicine; Daniel R. Gold, D.O. Departments of Neurology, Ophthalmology, Neurosurgery, Otolaryngology - Head & Neck Surgery, The Johns Hopkins School of Medicine
Given the finding seen in the first part of the video, which of the following associated features are most likely? (more than one answer may be correct); A.; Left homonymous visual field defect; B.; Right homonymous visual field defect; C.; Visual neglect and/or extinction; D.; Alexia without agraphia; E.; Left superior "pie in the sky" quadrantanopia; ; ; Answer: Both A and C are correct; ; ; A.; Correct. Poor or absent optokinetic responses to one side may be seen in patients with ipsilateral parietal lesions. While an isolated parietal lesion would cause an inferior quadrantanopia, in this patient, the right parietal and occipital lobes were affected by his anaplastic astrocytoma, which explains his complete left homonymous hemianopia and poor nystagmus when the optokinetic drum was moved to the ipsilesional or right hemisphere (normal optokinetic nystagmus when it is moved to the left). Lesions involving the optic tract, (entire) lateral geniculate nucleus or occipital lobe may cause a complete homonymous hemianopia but with normal bilateral optokinetic responses. ; B.; Incorrect. The visual field loss is contralateral to the side of absent optokinetic response.; C.; Correct. Right parietal lesions can also result in other higher order sensory deficits, including neglect and visual extinction to stimuli presented in the left visual field. Simultanagnosia may also be present usually when parietal lesions are bilateral as in Balint's syndrome.; D.; Incorrect. This patient has a right occipito-parietal lesion resulting in the loss of optokinetic nystagmus when stimuli are directly ipsilesionally, or to the right. A left occipital lesion that involves the splenium of the corpus callosum may result in alexia without agraphia. This is thought to be due to a right homonymous hemianopia from left occipital lobe involvement, and because the splenium is also affected, the visual information from the left hemifield makes it to the right occipital lobe, but this visual information cannot then be relayed to the dominant left hemisphere via the corpus callosum (a disconnection syndrome), so that reading is not possible. ; E.; Incorrect. The loss of unilateral OKN is due to a parietal lesion. "Pie in the sky" or superior quadrantanopic field deficits are often due to lesions involving the optic radiations travelling through the temporal lobe (Meyer's loop), although optic tract lesions (incongruous) or occipital lobe lesions (inferior to the calcarine fissure, congruous) are other causes of mainly superior homonymous visual field defects. ; ; Final Diagnosis: ; Poor optokinetic nystagmus when the optokinetic drum was directed toward (ipsilesional to) a right parieto-occipital anaplastic astrocytoma.
Spencer S. Eccles Health Sciences Library, University of Utah