MCQ Neurology Answer 6

The correct answer is A
Explanation

Atherothrombosis of the PCA is relatively uncommon, but when it occurs is generally in the proximal segment of the vessel. Sometimes thrombus may spread by contiguous ascent from the basilar apex.

PCA infarction rarely involves the entire arterial territory; and the variability of the resulting clinical deficits of primary sensory, visual and behavioral fiinction depend upon the degree of damage to the thalamus, occipital and inferomedial temporal lobes respectively.

Blockage of vessels derived from the proximal PCA can cause infarction in sensory and motor nuclei of the thalamus and nearby subthalamic structures. Such is the case when the thalamogeniculate branch is occluded, producing a distinctive syndrome of transient contralateral herniballismus and herniparesis with persistent hemihypesthesia and fleeting but recurrent contralateral pain .

When PCA infarction occurs as the result of occlusion beyond its proximal stem, obtundation and sleep disturbances are not present as reticular activating structures are spared. Herniparesis and third nerve dysfunction are absent because the cerebral peduncle is not injured.

Unilateral infarction of cerebrocortical structures within the occipital cortex manifest as contralateral hemianopia often sparing the macular region due to the dual supply of the occipital pole by PCA and MCA or ACA branches. With incomplete lesions of the primary visual receptive area of the calcarine region of the occipital lobe, the hernianopic loss may be more marked in the contralateral superior fields and less impaired in the inferior fields. With large cortical lesions involving occipital and temporal regions, a variety of behavioral syndromes may be present. Lesions of this type in the dominant hemisphere can produce alexia, anomia and amnesia. These deficits often occur without agraphia. The ability to name colors or recognize nonverbal symbols such as musical notes may be particularly impaired. When the non-dominanthemisphere is involved, spatial disorientation and the anomia for familiar faces (prosopagnosia) can occur.

Bilateral PCA infarcts of the temporal lobes may produce lesions of both hippocampi leading to a permanent severe amnesia termed Korsakoff's state. Bilateral infarction of the occipital lobes can produce Balint's syndrome of disordered volitional eye movements (ocular apraxia), imprecise visually guided eye movements (ocular ataxia), impaired visually guided limb movements (optic ataxia) and the inability to recognize and name multiple concomitantly viewed objects (simultanagnosia).

Category: Neurology MCQs