Final answer:
A tumor in the thoracic cavity can cause Horner's syndrome by disrupting the sympathetic nerve pathway that controls the eyelids, pupil size, and sweating. The tumor might compress or damage the sympathetic chain in the thoracic region, leading to ptosis, miosis, and anhidrosis on the affected side of the face.
Step-by-step explanation:
Horner's syndrome is characterized by a triad of symptoms: ptosis (dropping of the upper eyelid), miosis (pupillary constriction), and anhidrosis (decreased sweating) on the affected side of the face. These symptoms are a result of disruption to the sympathetic nerves supplying the eye and face, which can be caused by a thoracic cavity tumor.
The sympathetic nervous system pathways originate in the hypothalamus and descend through the brainstem and spinal cord to the thoracic region. A tumor in the thoracic cavity could compress or damage parts of this pathway, affecting the nerves that control the eyelids, pupil size, and sweating. Specifically, a tumor may impact the sympathetic chain that passes through the top of the lungs and over the rib at the base of the neck (the stellate ganglion) before reaching the face and eyes.
Therefore, a tumor within the thoracic cavity has the potential to disrupt normal autonomic function in the eye and facial region, leading to the characteristic symptoms of Horner's syndrome. The condition hence underscores the interconnectedness of the body's systems, with local abnormalities having widespread autonomic effects.