19th February 2024

A 78-year-old male with known hypertension presents to the acute medical department with vertigo and unsteadiness while walking. His wife reports a new hoarseness in his voice.

A 78-year-old male with known hypertension presents to the acute medical department with vertigo and unsteadiness while walking. His wife reports a new hoarseness in his voice. He denies any weakness at present. On examination, nystagmus on the left gaze was noted. Dysarthria was also noted. A left-sided ptosis was noted, and his pupil appeared constricted and smaller than his right pupil. 

Pain and temperature sensation was reduced along the left side of the face. When sitting, he appeared to lean towards his left side. Power examination of his extremities was normal, but he also appeared to have reduced pain and temperature sensation along the right side. An ischaemic stroke was found to be the underlying cause of his symptoms.

Which of the following areas of the brain has likely been affected?