A 68-year-old woman comes to the emergency department due to sudden-onset double vision that started immediately after she woke up. The patient notices that her vision worsens when looking to the right. She has no headache, weakness, or numbness. The patient has a prolonged history of hypertension, hyperlipidemia, and type 2 diabetes mellitus. Blood pressure is 160/90 mm Hg and pulse is 86/min and regular. Neurologic examination, including visual acuity, is normal with the exception of the ocular findings shown in the image below. A lesion involving which of the following structures is most likely causing the observed ocular findings in this patient?

Question

A 68-year-old woman comes to the emergency department due to sudden-onset double vision that started immediately after she woke up.  The patient notices that her vision worsens when looking to the right.  She has no headache, weakness, or numbness.  The patient has a prolonged history of hypertension, hyperlipidemia, and type 2 diabetes mellitus.  Blood pressure is 160/90 mm Hg and pulse is 86/min and regular.  Neurologic examination, including visual acuity, is normal with the exception of the ocular findings shown in the image below.  A lesion involving which of the following structures is most likely causing the observed ocular findings in this patient?

Quizplus · Accepted Answer

11ec160b_35d6_7109_9249_8dc5142f2114_MD0001_00 This patient has internuclear ophthalmoplegia, a disorder of impaired horizontal gaze caused by damage to the medial longitudinal fasciculus (MLF). The frontal eye field initiates horizontal gaze through the contralateral abducens (CN VI) nucleus, which communicates with the ipsilateral oculomotor (CN III) nucleus by way of the MLF. This allows for simultaneous activation of the lateral rectus muscle in the contralateral eye (abduction) and the medial rectus muscle in the ipsilateral eye (adduction), resulting in coordinated conjugate horizontal gaze. Unilateral MLF lesions typically occur in older patients with lacunar strokes in the dorsal pons or midbrain (pontine artery distribution) and result in impaired adduction of the ipsilateral eye during horizontal gaze, causing diplopia. Abduction in the contralateral eye is preserved (but often with gaze-evoked nystagmus). The pathways for convergence and the pupillary light reflex bypass the MLF lesion, so these reflexes are generally preserved. (Choice A) The abducens nerves innervate the lateral rectus muscles, which abduct the eyes. A lesion involving an abducens nerve would result in impaired abduction of the ipsilateral eye due to lateral rectus muscle palsy. (Choice B) The lateral geniculate nucleus is located in the thalamus and relays visual information to the ipsilateral primary visual cortex. Damage to this structure would result in a contralateral homonymous hemianopia. (Choice D) Unilateral infarction of the primary visual cortex in the occipital lobe (eg, posterior cerebral artery occlusion) typically results in contralateral homonymous hemianopia with macular sparing as the macula receives collateral circulation from the middle cerebral artery. (Choice E) Oculomotor nerve palsy (eg, ipsilateral mydriasis, ptosis, "down and out" deviation of the eye) may occur with microvascular nerve ischemia (eg, diabetes mellitus) or nerve compression (eg, posterior communicating artery aneurysm). (Choice F) The superior colliculus controls vertical gaze. Damage to the superior colliculus in the dorsal midbrain causes Parinaud syndrome (eg, upward gaze palsy, absent pupillary light reflex, impaired convergence). Educational objective: Internuclear ophthalmoplegia is a disorder of impaired horizontal gaze caused by a lesion in the medial longitudinal fasciculus (MLF). The affected eye (ipsilateral to the lesion) is unable to adduct while the contralateral eye is able to abduct (often with associated nystagmus). Convergence and the pupillary light reflex are preserved because these pathways bypass the MLF. __________ References: Brainstem pathways for horizontal eye movement: pathologic correlation with MR imaging. (http://www.ncbi.nlm.nih.gov/pubmed/23322826)

A 68-Year-Old Woman Comes to the Emergency Department Due to Sudden-Onset