A usually alert 80 year old man
lost consciousness. Upon awakening he complained of double vision and a tremor
in his left arm. Mental status was good and speech was articulate and
appropriate. The right eye had a dilated pupil and a lateral strabismus. On
attempted lateral gaze to the left, the right eye would not proceed across the
midline. Although vision was normal the right pupil did not constrict in either
the direct or consensual pupillary light reflexes. Hearing was normal as were CN
5-12. Pain and temperature sensation from the body and face were normal
bilaterally. There was diminished vibratory sense and muscle strength on the
left. The left arm showed an intention tremor, dysmetria and occasional
involuntary movements.
Which one of the following lesions does this patient have?
