bubble_chart Overview

The occipital lobe is relatively small, and tumors occurring solely in the occipital lobe are also rare. Occipital lobe tumors often simultaneously involve the parietal lobe and the posterior part of the temporal lobe. The most common tumors are gliomas, accounting for about 1.46% of intracranial gliomas; meningiomas account for about 0.74% of intracranial meningiomas; other tumors are even rarer. Physiologically, the occipital lobe is the highest-level visual analyzer, known as the "visual center." The main clinical manifestations caused by occipital lobe tumors are visual disturbances.

bubble_chart Clinical Manifestations

1. Depending on the location and extent of tumor growth, patients in the early stages often only experience visual field defects, amblyopia, or color vision loss on the contralateral side of the lesion.

2. When the tumor invades and damages the cuneus above the calcarine fissure of the occipital lobe, complete hemianopia does not occur, but only contralateral inferior quadrantanopia is present. If the lingual gyrus below the calcarine fissure is damaged, only contralateral superior quadrantanopia appears. Larger tumors may cause contralateral homonymous hemianopia. This is because the central visual field is controlled by both occipital lobes, and macular fibers project bilaterally, making them less susceptible to complete impairment. Therefore, in unilateral occipital lobe lesions, the central visual field often remains intact, a phenomenon known as macular sparing. Even with bilateral occipital lobe damage, complete blindness is rare, and the central visual field is usually preserved. Acute damage to one occipital lobe may cause transient total blindness, with the unaffected visual field recovering within hours, leaving contralateral homonymous hemianopia. Clinically, cases of complete blindness due to damage to the fibers between the bilateral occipital lobes and thalamus have been observed, but patients do not perceive their blindness, a condition known as Anton syndrome.

3. Visual seizures are a common symptom of occipital lobe tumors. Destructive lesions may lead to central hemianopia (macular sparing), cortical blindness, or visual agnosia. Irritative lesions may trigger visual seizures, sometimes as an aura of epileptic seizures, first described by Penfield in 1954, manifesting as simple visual hallucinations in the contralateral visual field. About 15–24% of occipital lobe tumors present with visual hallucinations. These hallucinations are typically unformed, such as flashes, bright spots, circles, lines, or colors, often appearing in the contralateral visual field with a floating sensation. Visual hallucinations may occur alone or as an epileptic aura. When epilepsy occurs due to occipital lobe lesions, the head and eyes often turn contralaterally, caused by stimulation of the "gaze center" in the occipital lobe.

4. Tumors in the left occipital lobe (dominant hemisphere) may also cause agnosia and visual distortions. Agnosia refers to the patient's inability to recognize objects based on their shape. The patient is not blind but cannot distinguish familiar people, objects, or colors, a condition often seen in lesions of the lateral left occipital lobe.

bubble_chart Auxiliary Examination

1. Skull Plain Film Skull plain film examination has almost become a routine method for intracranial tumors. The manifestations of occipital lobe tumors on skull plain films mainly depend on the nature and growth rate of the tumor, which may include increased intracranial pressure, skull destruction, or abnormal hyperplasia. This helps determine whether further auxiliary examinations are necessary.

2. Electroencephalogram (EEG) The EEG characteristics of occipital lobe tumors are characterized by localized slow waves, which often appear in the parieto-occipital or posterior temporal regions. Therefore, it is sometimes difficult to distinguish them from parietal lobe tumors, posterior temporal tumors, or temporo-parieto-occipital tumors. However, parietal lobe tumors often cause EEG changes in the posterior frontal or inferior parietal regions, showing more widespread and prominent delta and theta waves. Posterior temporal tumors are generally accompanied by abnormal waves in the anterior temporal region. Temporo-parieto-occipital tumors can cause delta waves of equal severity in the posterior temporal, parietal, inferior parietal, and occipital regions. The background alpha waves in EEGs of occipital lobe tumors are always impaired, with approximately half of cases showing significant suppression or disappearance of alpha waves on the affected side. Thus, the typical EEG pattern of occipital lobe tumors is localized delta waves against a background of desynchronization or significant alpha wave suppression in the occipital region, while asymmetry of fast waves is less common.

3. Ventriculography Due to the small size of the occipital lobe, tumors confined solely to this region are relatively rare. Tumors often compress the occipital horn of the ventricle, causing it to narrow or close. However, this must be distinguished from normal ventricular variations. If it falls within the range of variation, there will be no displacement of the lateral ventricular system. Larger occipital lobe tumors often protrude into the trigone of the lateral ventricle or the posterior part of the third ventricle. Tumors invading the parieto-occipito-temporal region may show filling defects in the body of the lateral ventricle, trigone, or temporal horn, with the third ventricle being pushed forward.

4. Cerebral Angiography The characteristic features of cerebral angiography in occipital lobe tumors are as follows: In the anteroposterior view, the lateral displacement of the anterior cerebral artery is minimal, with little change in its course. In the lateral view, the main trunk and convexity branches of the middle cerebral artery may be pushed forward, partially dispersed, straightened, or elevated. When the posterior cerebral artery is visualized, it may appear thickened, with its terminal branches either separated or compressed. Deep-seated tumors often invade the tentorium cerebelli, so the tentorial notch artery may be visualized and appear tortuous and thickened.

bubble_chart Differentiation

(1) The primary clinical symptom of occipital lobe tumors is changes in visual disturbances, with symptoms gradually progressing from mild to severe. It is important to differentiate these symptoms from visual disturbances caused by lesions at various sites along the visual pathway. However, lesions at different locations along the visual pathway produce distinct clinical manifestations. The typical symptoms of occipital lobe tumors are Anton syndrome and unformed visual hallucinations, which are not seen in lesions of other regions. For example, visual hallucinations in temporal lobe tumors are usually formed and accompanied by other symptoms of temporal lobe lesions. Careful examination can easily distinguish them.

Another symptom of occipital lobe tumors is contralateral homonymous hemianopia. Since the central visual field is governed by both occipital lobes, with widely distributed fibers that are less likely to be entirely affected, unilateral occipital lobe lesions often spare the central visual field, a phenomenon known as macular sparing. This feature helps differentiate it from contralateral homonymous hemianopia caused by compression of the optic radiation by parietal or temporal lobe tumors.

(2) Visual seizures occurring in occipital lobe tumors should be distinguished from visual hallucinations seen in migraine, certain drug poisoning diseases, or schizophrenia. The characteristics of visual seizures caused by occipital lobe tumors include: the hallucinations appear in a relatively fixed location, typically within the contralateral visual field of the lesion; the frequency of seizures gradually increases, and as the seizures become more frequent, other localizing symptoms such as hemianopia, agnosia, and aphasia may appear; the seizures are unrelated to the environment. In contrast, hallucinations in schizophrenia are related to the environment and are accompanied by other psychiatric symptoms. Additionally, visual seizures caused by tumors are often accompanied by head and eye deviation toward the side opposite the lesion. Migraine and certain drug poisoning diseases do not produce the characteristic visual hallucinations seen in tumors, making them easier to differentiate.