Final answer:
The lesion is likely located at the lateral aspect of the medulla oblongata on the left side, known as Wallenberg's syndrome or lateral medullary syndrome, which can be confirmed with neuroimaging such as an MRI.
Step-by-step explanation:
The lesion is likely located in the brainstem, specifically at the lateral aspect of the medulla oblongata on the left side, known as Wallenberg's syndrome or lateral medullary syndrome. The symptoms described indicate a neurological condition that correlates with Wallenberg's syndrome or lateral medullary syndrome. This syndrome is typically a result of a stroke or vascular lesion in the lateral part of the medulla oblongata within the brainstem.
Hemisensory loss on the left side indicates disruption of sensory pathways, while Horner's syndrome suggests involvement of the sympathetic fibers, which also run through the medulla. The presence of right facial sensory loss can be explained by the involvement of the trigeminal nerve nuclei, which are located in close proximity to where this lesion typically occurs. It is important to use neuroimaging, like magnetic resonance imaging (MRI), to confirm the diagnosis and initiate appropriate treatment.