Because most of the occipital lobe is involved in visual function, occipital lobe seizures are frequently preceded by a visual aura. Visual auras include ictal amaurosis or hemianopsia, elementary or complex visual hallucinations, and visual illusions (85,94).
Ictal amaurosis describes ictal blindness and is uncommon. It may be preceded by ictal hemianopsia. If hemianopsia occurs, it has lateralizing significance to the contralateral occipital lobe. Ictal amaurosis lasts seconds to minutes and may be the sole manifestation of an occipital lobe seizure (95). It can be described by the patient as a whiteout or blackout. There may be initial blurring (96). Ictal blindness has been associated with the visual association cortex rather than with the primary visual cortex (97). Elementary visual hallucinations are images of shapes, colors, patterns, or waves that may have a flickering component (6,98). These can occur in one hemifield and, if so, they lateralize to the contralateral hemisphere. Elementary visual hallucinations are associated with the primary visual cortex. It has been shown that if elementary visual hallucinations are stationary they originate in area 17. If movement of the phosgens is present, they may originate in area 18 or 19 (6,99).
Complex visual hallucinations include a variety of images, which includes scenes, persons, animals, and material items. The images are usual uniform and stereotyped but patients with variable hallucinations are reported (100). Formed and complex visual hallucinations suggest involvement of visual association cortex.
Visual illusions include macropsia, micropsia, metamorphopsia, and pallinopsia. Patients with macropsia perceive an object bigger than its actual size. Patients with micropsia perceive an object smaller than the actual size. Metamorphopsia presents as distortions of form, size, or color. Pallinopsia is a visual preservation of an image long after the cessation of the visual stimulus (101). Visual illusions are thought to orginate in the visual association cortex, therefore the tem-poroparietal junction may also be involved. Distortions of body image have been described with parietal lobe seizure onset (47); however, this most likely is a disturbance of self perception rather than a visual illusion.
In occipital lobe seizures, a pulling or moving sensation in the eyes has been reported without detectable movements (94,102). Penfield observed eye fluttering with stimulation of the occipital lobe (6). Bilateral rapid eye blinking as a manifestation of occipital lobe seizures was confirmed with intracranial studies (94,103).
Ictal nystagmus is a rare seizure manifestation and has been associated with occipital seizure onset. Horizontal nystagmus has been reported in several patients with epileptic involvement of the cortical saccade region, and lateralization of the slow phase to the contralateral side has been demonstrated (104).
In a previous study, contralateral eye deviation was observed in thirteen of twenty-five patients with occip-tal seizures onset; however, ipsilateral eye-deviation was observed in three (94). Eye deviation was also fre quently observed in children with occipital lobe seizures (105). Ajmone-Marsan proposed three propagation patterns of occipital lobe epilepsy: mesial suprasylvian, lateral suprasylvian, and infrasylvian (4). In mesial suprasylvian spread, bilateral or unilateral tonic posturing may be observed due to the involvement of the SMA. Lateral suprasylvian spread results in clonic motor activity due to the involvement of the motor cortex, and infrasylvian spread may resemble a temporal lobe seizure. Ajmone-Marsan's description of spread patterns was later confirmed by intracranial EEG studies (94,106-109). Often patients are amnestic for the initial aura or symptoms; therefore, occipital lobe seizures can be mistaken easily as seizure either of temporal or frontal origin.
Seizures originating in the occipital lobe occur most commonly in benign childhood epilepsy with occipital paroxysms (110). Seizures begin with visual symptoms (as described earlier) and may progress to head turning, eye-deviation, vomiting, and hemiconvulsions following the described electrical propagation patterns.
Benign childhood epilepsy with occipital paroxysms manifests itself in childhood and is characterized by mainly nocturnal seizures.
Occipital lobe seizures may also be caused by lesions or cortical dysplasias, but are more difficult to recognize if they do not clearly present with visual symptoms.
Migraine is associated with visual scotoma that may resemble the elementary visual hallucinations as seen in occipital lobe seizures. It has been suggested that epileptic visual hallucinations are colored and migraine scotoma are black and white (111). However, because occipital epilepsy can be accompanied by vomiting and headaches, clinical distinction between epilepsy and migraine can be difficult without additional testing (refer to Chapter 9).
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