Clinical manifestations

Presentation and course

Seizure of the posterior neocortex can be recognized by the initial symptom or sign (aura). The subsequent characteristics usually reflect spread patterns, whereas initial symptoms often help identify the region of seizure origin (83). One characteristic that posterior neocortical seizures share is the tendency to have multiple spread patterns (70; 71; 90; 89; 40; 30). This can occur among different patients or among different seizures in the same patient. Therefore, patients with this type of seizure origin can present with stereotyped but different-appearing clinical seizures depending on direction of seizure spread, or, conversely, individual patients can have seizures that are not stereotyped from one to another, strongly suggesting multifocality.

Occipital lobe seizures. Occipital lobe seizures can be divided into subjective and objective manifestations.

Subjective initial signs. Although visual alterations are the hallmark of occipital lobe seizures, they occur only in 47% to 85% of patients (45).

Elementary visual hallucinations. Elementary visual hallucinations occur in several forms (11; 11; 70; 71; 90; 10). Most often, visual hallucinations are multiple spots of light, steady or flashing. A white light with a greenish tinge (phosphene) is commonly described. Descriptions of multicolored or monochromatic light have been reported as well. The visual hallucinations can be central or lateralized. When lateralized, they occur contralateral to the seizure focus. If they appear in the upper quadrant, the seizure discharge is below the calcarine fissure. Symptoms in the inferior quadrant have an analogous anatomical relationship. The visual hallucination may move horizontally, usually from the side contralateral to the seizure focus. Elementary visual hallucinations are the most common aura of occipital lobe epilepsy (45).

Ictal amaurosis. Visual loss at seizure onset is almost as common a symptom of occipital lobe seizure onset as elementary visual hallucinations, but it is not as widely recognized (11; 11; 70; 71; 90; 10; 75; 48). Patients may not complain of visual loss unless specifically questioned (83). Visual loss is usually bilateral, but homonymous hemianopsia contralateral to the seizure discharge can occur. It may be possible that the patient often does not perceive hemi-field deficits. Ictal amaurosis usually consists of a blackout, but whiteouts or diffuse perceptions of color can occur. Ictal amaurosis can be prolonged and represent status epilepticus amauroticus (Ayala 1929; 75).

Complex visual hallucinations. Complex visual hallucinations are less common than elementary visual hallucinations (45). They consist of scenes or people as epileptic aura. They are thought to be associated with seizure onset in the occipital-temporoparietal junction (10). Capgras delusions involving belongings have also been rarely reported (54).

Visual illusions. Micropsia (objects appearing smaller), macropsia (objects appearing larger), metamorphopsia (distortion of images), and achromatopsia (loss of color vision) can also be clinical manifestations of seizures originating in the occipital-temporoparietal junction.

Eye movement sensations. The sensation of eye movement in the absence of detectable movement has been reported as a sign of occipital seizure origin (05; 41; 70; 71; 90). Sometimes this symptom is described as a sensation of the eyes being pulled back in the head. Although this might actually be occurring, detection would require direct examination during the symptom.

Diplopia. Diplopia has rarely been reported as an epileptic manifestation (33), but the localizing value is not known.

Objective initial signs.

Eye deviation. Early deviation of the eyes with or without head deviation is frequently reported in seizures beginning in the occipital lobe (80; 60; 70; 71; 90). Although the literature strongly favors contralateral deviation, there are rare exceptions (70; 71; 90). Electrical stimulation studies in humans and animals have reproduced contralateral deviation.

Epileptic nystagmus. Nystagmus as a manifestation of epileptic discharges has been reported repeatedly (29; 05; 55; 60; 70; 71). There is disagreement, however, of the lateralizing significance of the fast and slow components (47). Lee and colleagues reviewed the literature and noted that in all 33 patients with unilateral horizontal nystagmus, the nystagmus was beating away from the side of ictal discharges (50). Monocular isolated epileptic nystagmus has been rarely described (56).

Blinking or eyelid flutter. Forced blinking or eye fluttering has been observed in up to 50% of patients with occipital lobe seizures (05; 60; 90; 04). Depth electrode studies in 24 patients have confirmed ictal blinking (mostly bilateral) as being localized to mostly occipital and occipital-temporal seizures with less frequent localization from the medial temporal and insulo-opercular (49).

Signs and symptoms of propagation. Occipital seizure foci are uniquely situated to allow multiple possible propagation patterns (01; 70; 71; 45). Occipital lobe seizures can spread above or below the sylvian fissure, medially or laterally, ipsilateral or contralateral to the side of origin.

Several reports have noted that complex visual hallucinations usually follow elementary visual hallucination, suggesting propagation outside of the occipital lobe (55; 60; 11; 90). Complex visual hallucinations may require involvement of both limbic and neocortical structures. Propagation from the occipital lobe to medial temporal structures has been well documented (55; 60; 90). Automatisms indistinguishable from those of typical temporal lobe epilepsy occur (79; 71; 72). Suprasylvian spread results in various focal tonic and clonic motor manifestations (79; 11; 70; 71). Although contralateral propagation with lateralized clinical manifestations is theoretically possible, this has been only partially documented with intracranial recording (79).

The potential for multiple spread patterns holds true among different patients and within individual patients (79). Patients with occipital lobe seizure origin, therefore, do not present with any specific seizure pattern, and some may have several different seizure types, suggesting multifocal disease.

Postictal vomiting and headaches are common with occipital lobe seizures (45; 23). Secondary generalization is frequent (61; 62; 48). Prolonged visual nonconvulsive status epilepticus has been repeatedly reported (06; 45).

Parietal lobe seizures. Similar to occipital lobe seizures, parietal lobe seizures can be divided into subjective and objective manifestations. Although certain symptoms and possibly some signs help identify parietal lobe origin, much of the parietal lobe is silent with respect to clinical seizure manifestations. In addition, some aspects of seizure-induced parietal lobe dysfunction might not be apparent without specific testing, ie, testing of various cortical somatosensory functions.

An example of this is found in the classic monograph Epilepsy and the Functional Anatomy of the Human Brain (65): Patient J. St. had a seizure limited to the parietal lobe recorded during corticography under local anesthesia. Two-point discrimination was impaired during the seizure but returned to normal after the seizure. Such a serendipitous observation would rarely be possible. It would also require that the seizure remain limited to the parietal lobe, which is often not the case.

Subjective manifestations.

Paresthesias. Paresthesias are usually contralateral to the side of seizure onset (89; 18; 40; 72). They consist of localized numbness or a "pins and needles" sensation. Unpleasant crawling sensations have also been described. When localized at onset, they may remain localized or they may exhibit a march similar to focal clonic motor seizures (Jacksonian march). Ipsilateral or bilateral paresthesias suggest involvement of secondary parietal sensory systems (89). Contralateral paresthesias are the most common subjective manifestation of parietal lobe seizure origin, but they probably occur in less than half of the patients with this type of seizure disorder.

Ictal pain. Ictal pain is rare, and when it occurs in isolation misdiagnosis is common (77). Ictal pain is usually a sign of parietal lobe seizure origin (77). The pain usually consists of a burning, unpleasant dysesthesia with lateralization and distribution characteristics similar to those described for paresthesias. Severe, cramping, lateralized abdominal pain has also been equated with parietal lobe seizure origin (77; 64).

Alien hand (La main etrangere). The sensation that a body part, usually a hand, does not belong to the person is another rare parietal lobe seizure symptom (52). This has been documented with intracranial recording and successful surgery (77).

Vertigo. True vertigo is reportedly due to seizure activity in the temporoparietal junction. Although it is a well-established seizure symptom, epileptic vertigo is rare, and the exact neocortical representation has not been documented with precision (76). In a systematic review of epileptic vertigo and dizziness that reviewed 84 studies and 11,354 patients, localized EEG was more frequently temporal, with parietal EEG abnormalities noted only in 11.8% (82).

Sensations of movement. During vertiginous seizures, the environment may appear to move. In addition, the sensation of body part movement without observable movement has been reported as a symptom of parietal lobe seizure activity (65). A case report implicated the precuneus (57). Body image disturbances may also be seen with precuneal epilepsy (91).

Disorders of reading and language. The wide variety of reading, writing, and speech disorders associated with structural damage of the language-dominant parietal lobe might occur transiently as ictal symptoms during limited parietal lobe seizures but, other than nonspecific dysphasic disorders, these have not been selectively demonstrated.

Proprioceptive induced seizures (motor seizures triggered by proprioceptive stimuli of extremities) are a rare manifestation of parietal lobe seizures (92).

Objective disorders. The parietal lobes are generally associated with processing sensory information and, as such, would not be expected to produce much in the form of objective ictal behavior (89; 02). Exceptions might be demonstrable disorders of language mentioned previously or curious reactions to unpleasant stimuli, such as severe pain. Inhibitory motor or paralytic seizures can be associated with parietal lobe seizure origin (77). Ictal hemiballism has been associated with seizure onset in the inferior parietal lobule or the parietal operculum (28).

Signs and symptoms of seizure propagation. Posterior propagation from the parietal lobe can result in a patient experiencing elementary visual hallucinations or ictal amaurosis. Anterior spread can produce focal clonic motor activity. Asymmetrical tonic motor activity is often seen with seizures of parietal lobe origin during which there is intracranial recording evidence for and against spread to the supplementary motor area (35; 89; 77). Inhibitory or hemiplegic seizures may occur, but it is not known whether this represents spread beyond the parietal lobe (77; 86). Inferior spread into the temporal lobe has been well documented with intracranial recording (89). It has been suggested that posterior parietal lobe seizure origin is most often associated with spread to the temporal lobes (40). Inferior parietal seizures may be associated with grimacing, expressing itself as both laughter and disgust (53).

Prognosis and complications

Prognosis, of course, depends on the underlying etiology of the seizures. The benign idiopathic occipital lobe epilepsies respond well to medications (59; 75; 26). Symptomatic occipital lobe epilepsy may respond to regular antiseizure medications, but if this is not successful, epilepsy surgery should be considered. Epilepsy surgery is less successful in the posterior neocortex than in other parts of the brain due to the large cortical surface (16). Approximately a 50% seizure-free outcome is reported in most series (70; 90; 61; 40; 72; 04; 10; 20; 16; 46; 81), although surgical success rates above 80% in occipital lobe epilepsy and above 60% in parietal lobe epilepsy have also been reported (81).

Lately, there has been discussion about whether focal childhood epilepsies such as idiopathic childhood epilepsies with occipital paroxysms cause neuropsychological impairment. A study showed that there is impaired object identification in COVE, formerly known as idiopathic childhood occipital epilepsy, possibly related to the amount of epileptiform activity (14; 66). Others found overall decreased performance in visuomotor coordination, memory, and attention in a similar patient population. Drug resistant epilepsy related to posterior cortex epilepsy in a pediatric cohort showed impairment in working memory and processing speed (73).

Clinical vignette

A 54-year-old woman with a longstanding history of depression and anxiety was referred for episodes of “arm cramping” at night. She described those episodes as extremely painful, occurring frequently and with some arm shaking. She also stated that during those episodes she had a feeling such that her arm did not belong to her. The episodes started three years prior to her clinic visit. She had a history of PTSD and abuse. An MRI of her brain was normal and previous interictal EEGs were normal. Because of her long previous psychiatry history, her episodes were thought to be psychogenic. To clarify the diagnosis she was admitted for video EEG. During the first night, an episode was recorded in which the patient reported pain in her right arm. She then had dystonic posturing and severe pain in the right arm. She yelled and screamed as long as the pain lasted. She was completely conscious throughout. The EEG showed a clear rhythmic seizure discharge over the left centroparietal region. The patient became seizure free with carbamazepine.

Biological basis

Localization

By definition, seizures of the posterior neocortex originate in regions of the cerebral cortex behind the rolandic fissure, not including the posterior limits of the temporal lobe. Certain initial signs or symptoms localize the region of origin. For example, elemental visual hallucinations or ictal amaurosis localize to the occipital pole, whereas localized paresthesias would implicate the contralateral primary sensory cortex (90; 89). Visual auras of any type do not localize to a certain subregion of the occipital lobes (10). Even primary elementary hallucinations are not definitely associated with seizure onset in the mesial occipital cortex (13; 45). Bien and colleagues suggested that visual auras can also occur with anteromedial temporal lobe epilepsy (10) and are not entirely specific for occipital lobe epilepsy. Only visual field deficits seem to reliably localize to the medial occipital cortex (13).

Etiology and pathogenesis

The same principles associated with the causes of human epilepsy apply to parietal and occipital lobe seizures. These have been summarized by Engel and include nonspecific predisposing factors, specific epileptogenic disturbances, and precipitating factors (25). The causes are variable and include among others genetic disorders, postanoxic brain injury, neoplastic brain disorders, infections including neurocysticercosis, disorders of cortical development, and immune-mediated inflammatory disorders.

Pathophysiology

The underlying pathophysiology for any type of focal seizure is a disturbance of excitation and inhibition on a neuronal level that finally leads to hypersynchronization and propagation of seizure activity.

The tendency toward multiple spread patterns, although not unique, is characteristic of seizures of the posterior neocortex. The same is not true of mesial temporal lobe seizures or most frontal neocortical seizures. The pathophysiology of this characteristic, although not known, almost certainly reflects the rich connectivity of these regions. Disorders of neural development, neoplasms, posttraumatic encephalomalacia, and vascular malformations are the pathological substrate for posterior neocortical seizures (20).

Epidemiology

There are scant studies specifically addressing the epidemiology of parietal and occipital lobe seizures. The general principles are addressed by Tellez-Zenteno, who reviewed the epidemiology of temporal lobe seizures (84). Focal seizures, including parietal and occipital lobe seizures, are estimated to represent 60% of patients with epilepsy. The prevalence of epilepsy ranges from 4 cases per 1000 in developed countries to 57 cases per 1000 persons in developing countries, especially those afflicted by neurocysticercosis. The median incidence of epilepsy in developed countries ranges from 25 to 50 per 100,000 person-years and is as high as 115 per 100,000 person-years in the developing countries. The incidence is highest in early adulthood in the developing world, whereas it is highest in children and the elderly in developed countries.

Prevention

Seizure precautions are the same as in any other seizure disorders. The general principles of prevention that are applicable to focal epilepsy are relevant to parietal and occipital lobe seizures. Prevention strategies are also dependent on the etiology, which commonly includes structural abnormalities.

Differential diagnosis

Confusing conditions

Because seizures originating in the posterior neocortex can have multiple spread patterns, they can mimic other types of seizures such as lateral temporal, mesial temporal, or frontal lobe seizures (01; 70; 72; 90; 89; 88). The overall seizure pattern can, therefore, be misleading. Occipital lobe seizures can often masquerade as temporal lobe seizures. In a retrospective case-control series, visual symptoms were present in only 8 of 19 occipital lobe seizure patients, and occipital spikes were found in only one third (03).

Seizures originating in the parietal lobe seem to be particularly prone to be devoid of localizing information. In two studies of parietal lobe seizures, only half of the patients had clinical findings suggesting parietal lobe seizure origin (89; 18). All patients in both studies had parietal lesions on MRI that served to identify the region of seizure origin. Differential diagnosis includes nonepileptic psychogenic seizures with visual complaints or somatosensory complaints. As occipital lobe seizures are frequently followed by postictal headache, migraine is often considered an alternative diagnosis. Occipital epilepsy and migraine can be indistinguishable, unless the patient has generalized tonic-clonic convulsions or seizures with loss of consciousness (21). As pure sensory parietal seizures can present with prolonged paresthesias, those seizures are often mistaken as transient ischemic attacks. Video/EEG monitoring should be utilized to clarify the differential diagnosis.

Associated and underlying disorders

Self-limited childhood epilepsies with occipital lobe spike (COVE type and SeLEAS). Occipital lobe seizures can occur in the benign idiopathic childhood epilepsies with occipital lobe spikes (34). Two types of benign idiopathic occipital epilepsy have been described (Table 1): a syndrome with early onset (SeLEAS: formerly known as Panayiotopoulos type or benign childhood seizures susceptibility syndrome) and a late-onset form (COVE syndrome: formerly known as Gastaut type). It has been discussed whether in Panayiotopoulos type the seizures onset zone is truly in the occipital lobe or whether the epileptogenic zone is more widespread in this particular syndrome (63). Genetically, both syndromes show a complex pattern of inheritance (83).

SeLAS (self-limited epilepsy with autonomic seizures) has a mean onset age of 4.7 years. Seizures mainly consist of gaze deviation, ictal vomiting, and autonomic symptoms. Nonconvulsive prolonged episodes are common. EEG shows typical posterior paroxysmal epileptiform activity. Seizures may remit spontaneously after one to two years (26).

COVE (childhood occipital visual epilepsy) manifests between the ages of 7 and 9 years, and seizures are mainly characterized by visual hallucinations, ictal amaurosis, and postictal headaches. Status epilepticus is rare. Seizures readily respond to antiepileptic medications. MRI is normal (17).

Table 1. Clinical Characteristics of Syndromes with Occipital Lobe Seizures

Symptomatic occipital lobe epilepsy. Symptomatic occipital lobe epilepsy is associated with abnormal pathology in the occipital lobes. This includes tumors, gliosis, vascular malformations, and malformations of cortical development. Age of onset and prognosis is variable due to the underlying etiology (Table 1).

Other systemic diseases associated with occipital lobe seizures. Occipital lobe seizures occur in celiac diseases with occipital lobe calcifications (31; 09) and Sturge-Weber variant (22). Posterior reversible encephalopathy syndrome (PRES) due to hypertension or immunosuppression can be the cause of occipital lobe seizures (51).

Overlap of occipital lobe epilepsy with photosensitive genetic generalized epilepsy. Variants have been observed in patients with retinoid related orphan receptor beta genetic variants with patients exhibiting both generalized photosensitive seizures and occipital lobe seizures. The median age of onset of these patients is 3.5 years, with many suffering from intellectual disability (68). POLE (photosensitive occipital lobe epilepsy formerly known as idiopathic photosensitive occipital lobe epilepsy) is a syndrome that should be suspected in patients with seizures with occipital semiology, photosensitivity, and normal MRI (36).

No recognized diseases or syndromes are associated exclusively with parietal lobe seizures, and parietal lobe epilepsy is generally thought to be symptomatic in origin.

Diagnostic workup

If, after a thorough history and examination, focal epilepsy of any type is suspected, a high-resolution, if possible, 3T MRI should be obtained early in the course of the evaluation to search for a structural cause of the seizures. As parietal lobe seizures are difficult to diagnose and may imitate other focal epilepsies, MRI may be the only diagnostic test to suggest the parietal lobe as the site of seizure onset (67). Interictal EEG is usually performed to assess for epileptiform activity. EEG may show occipital or parietal spikes, but can be misleading and localize to the posterior temporal lobes or other cortical areas (67). Ictal EEG can show occipital or parietal rhythmic epileptiform activity.

Even prolonged monitoring is often not informative in patients with posterior neocortical seizure origin due to false localization on scalp EEG (11; 89; 18; 32). If a detected structural lesion is considered benign or if the MRI is normal, further diagnostic workup is not required, and medical management should be initiated or continued. If medications fail to control seizures and surgical intervention is being considered, the diagnostic evaluation becomes more extensive (43).

Detection of a single, well-circumscribed epileptogenic lesion greatly simplifies the presurgical evaluation, and epilepsy surgery will be more successful compared to patients with nonlesional epilepsy (87). Prolonged video-EEG monitoring, ictal SPECT, FDG-PET, additional high-resolution MRI, MRI-PET fusion, magnetoencephalography, and intracranial EEG studies are essential to localize the seizure onset zone for later resection (69). Multilobar resections of the posterior neocortex also have a good success rate (74). The neuropsychological profiles of parietal and occipital lobe epilepsy are not well defined, though some studies have shown visuoconstruction and verbal and executive deficits (85).

Management

No antiseizure drugs preferentially work on the posterior neocortex. Any of the approved antiseizure medications are effective; however, not all are approved as initial therapy or monotherapy. Antiseizure medications should be chosen based on the side effect profile and comorbidities of the patient. Reproductive and psychosocial factors are other considerations.

If seizures do not respond to medical treatment, resective surgery should be considered and referral to a comprehensive surgical epilepsy center initiated even if no clear lesion on MRI can be identified (43).

Success rate of surgical intervention is variable (70; 89; 81). In a review and metaanalysis of 27 published case series involving occipital and posterior quadrant epilepsy surgery, an Engel class I outcome was observed in 65% of patients (38). Vagal nerve stimulation is another effective adjunctive treatment (44). Responsive neurostimulation may be another effective alternative and has been available since 2013 with a median reduction of seizures of 53% at two years (39). There are also some studies exploring the use of targeting with neurostimulation the pulvinar nucleus in patients with posterior epilepsies (15). Total and partial posterior quadrant disconnection has also been performed in select patients (58).

Special considerations

Pregnancy

Consideration is similar to any other patients with focal seizures and includes the risk of teratogenesis from antiseizure drugs (07).

Anesthesia

Anesthetic considerations are similar to any other patients with focal seizures and are dependent on underlying etiology. Direct cortical stimulations to localize the motor strip during surgical resection of lesions in proximity to primary somatosensory cortex with parietal lobe seizures may necessitate the avoidance of muscle relaxants (19).