A 59-year-old man comes to the office due to diplopia and a drooping right eyelid. His symptoms began a day earlier and have since worsened. Physical examination shows a dilated right pupil that is nonreactive to both light and accommodation. There is vertical and horizontal diplopia. When the patient is asked to stare straight ahead, the right eye is directed inferiorly and laterally with respect to the left eye. MRI of the brain reveals an aneurysm involving the right posterior communicating artery. Which of the following muscles is most likely to remain functionally intact in this patient?

Question

A 59-year-old man comes to the office due to diplopia and a drooping right eyelid.  His symptoms began a day earlier and have since worsened.  Physical examination shows a dilated right pupil that is nonreactive to both light and accommodation.  There is vertical and horizontal diplopia.  When the patient is asked to stare straight ahead, the right eye is directed inferiorly and laterally with respect to the left eye.  MRI of the brain reveals an aneurysm involving the right posterior communicating artery.  Which of the following muscles is most likely to remain functionally intact in this patient?

Quizplus · Accepted Answer

11ec160b_35a7_bf89_9249_330a37c6e74a_MD0001_00 This patient has a right oculomotor nerve (CN III) palsy secondary to a compressive aneurysm. Lesions involving CN III cause ptosis (drooping of the upper eyelid) and impair adduction, depression, and elevation of the eye. As a result, diagonal (eg, horizontal and vertical) diplopia is frequently present. The eye rests in a "down and out" position due to the unopposed action of the superior oblique (CN IV) and lateral rectus (CN VI) muscles. Pupillary constriction and accommodation can also be affected as CN III carries parasympathetic fibers to the ciliary muscle and the iris sphincter. CN III palsy can be due to a variety of causes, including intracranial tumors or aneurysms, nerve ischemia, and head trauma. Aneurysms causing CN III palsy most often involve the posterior communicating artery. When due to an aneurysm, symptoms that develop acutely are especially worrisome as they suggest active aneurysmal dilation and possible impending rupture. (Choices A, B, D, E, and F) All of these muscles are innervated by CN III, so their function will be impaired in this patient. Educational objective: Lesions involving the oculomotor nerve (CN III) cause ptosis, a downward and laterally deviated eye, impaired pupillary constriction and accommodation, and diagonal diplopia. The most dreaded cause of CN III palsy is an enlarging intracranial aneurysm.

A 59-Year-Old Man Comes to the Office Due to Diplopia