Final answer:
A stroke characterized by contralateral hemiplegia and ipsilateral cranial nerve involvement indicates a lesion in the brainstem where motor and cranial nerve pathways are in close proximity, commonly due to an ischemic event.
Step-by-step explanation:
An occlusion or stroke that is characterized by 'alternate' syndromes, which presents as contralateral hemiplegia and ipsilateral cranial nerve (CN) involvement, typically occurs in the brainstem. This specific location is known as a 'crossed syndrome' because the symptoms affect opposite sides of the body. Lesions in the brainstem can result in this pattern because the motor pathways descend from the cortex, crossing to the opposite side lower in the brainstem or spinal cord, while the cranial nerve nuclei are located at various levels of the brainstem.
For example, a lesion in the lateral medulla (Wallenberg syndrome) would result in contralateral loss of pain and temperature sensation in the body and ipsilateral deficits like Horner's syndrome, ataxia, and dysphagia due to involvement of the descending sympathetic tract, cerebellar connections, and CN IX and X, respectively. Strokes in this region are typically of the ischemic variety, where a blockage or narrowing of the blood vessel disrupts the blood flow.