SEIZURE SEMIOLOGY TWEETORIAL
#Epilepsy #Neurotwitter #Seizure #Semiology
🧵1/ What is a visual aura?
Visual auras consist of brief, stereotypical, visual hallucinations of static, flashing or moving lights in different shapes and colors, complex hallucinations and illusions.
2/ Visual auras can be classified into many types- simple visual hallucinations, complex visual hallucinations, visual illusions and ictal amaurosis. #Seizure #Semiology #Neurotwitter
3/ Simple visual hallucinations are typically described as flashing lights of different shapes-circles, stars, halo, lines, spots etc. These may or may not be colored. They may or may not move. These always lateralize to the contralateral hemisphere. #Neurotwitter
4/ Simple visual hallucinations have a very high localizing value to the occipital lobe. In Penfield & Kristiansen, 11 patients had visual sensation as the initial seizure manifestation. In all patients, the epileptogenic lesion was in the occipital lobe.
5/ The symptomatogenic zone of simple visual hallucinations includes primary and secondary visual areas in the occipital lobe- BA 17, 18 and 19. Functional areas of the visual cortex are classified as V1-V5 and don't necessarily agree with Brodmann areas.
6/ It is generally agreed that static simple visual hallucinations originate from V1 (which is mostly located on the mesial occipital surface; pericalcarine cortex; BA 17) whereas moving simple hallucinations localize to V2 and V3.
7/ First reports of visual hallucinations secondary to cortical stimulation came from Krause in 1924 and Foerster in 1936. This was followed by the pioneering work of W. Penfield & H. Jasper. They only found simple visual auras in occipital lobe stimulations.
8/ Complex visual hallucinations consist of formed images, which may appear as animals, people or scenes. These are believed to reflect activation of a wide visual association cortex. They can be elicited from mesial parietal, lateral and basal occipitotemporal regions.
9/ Visual illusionary auras (micropsia, macropsia, metamorphopsia, teleopsia, pelopsia, palinopsia) reflect misperceptions of real external visual stimuli. They are often clubbed under 'psychic auras' & don't have a discrete localization, but are seen with temporal lobe seizures.
10/ Ictal amaurosis is a negative manifestation of a seizure discharge affecting the visual cortex. The temporary blindness can be bilateral or restricted to one hemifield or one quadrant.
11/ The first case of occipital lobe epilepsy with visual aura was reported by Gowers in 1879. His patient described a brilliant image of a "gold serpent" with his seizures. This was further elaborated by Gordon Holmes and Penfield with his colleagues.
12/ Multiple studies of patients with occipital lobe epilepsies has shown that majority of the patients have a visual hallucination as the initial manifestation of the seizure.
13/ In a series of 42 patients with refractory occipital lobe epilepsy from @TheNeuro_MNI between 1930 and 1991, 73% had visual auras, majority of which were simple hallucinations, whereas 12 patients had ictal blindness.
14/ Conclusion- The simple visual hallucinations have a very high localizing value to the occipital lobe. When these are lateralized, the seizure onset zone is contralateral. Identification of visual auras can significantly aid in localizing the EZ to the occipital lobe.
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