A 65-year-old man is brought to the emergency department after he suddenly became unresponsive at home. On arrival, paramedics found him pulseless with ventricular fibrillation. After 10 minutes of cardiopulmonary resuscitation, the patient regains spontaneous circulation. In the hospital, he is intubated and placed on mechanical ventilation. His vitals remain stable. A therapeutic hypothermia protocol is initiated. After 72 hours following rewarming, he remains comatose with fixed and dilated pupils. There is no direct or consensual pupillary response to light. MRI of the brain reveals diffuse loss of grey-white matter differentiation with sulcal effacement. Damage to which of the following areas of the brain is the most likely cause of this patient's pupillary findings?

Question

A 65-year-old man is brought to the emergency department after he suddenly became unresponsive at home.  On arrival, paramedics found him pulseless with ventricular fibrillation.  After 10 minutes of cardiopulmonary resuscitation, the patient regains spontaneous circulation.  In the hospital, he is intubated and placed on mechanical ventilation.  His vitals remain stable.  A therapeutic hypothermia protocol is initiated.  After 72 hours following rewarming, he remains comatose with fixed and dilated pupils.  There is no direct or consensual pupillary response to light.  MRI of the brain reveals diffuse loss of grey-white matter differentiation with sulcal effacement.  Damage to which of the following areas of the brain is the most likely cause of this patient's pupillary findings?

Quizplus · Accepted Answer

11ec160b_3594_1050_9249_2f849e808d0f_MD0001_00 This patient's presentation and MRI findings (eg, loss of grey-white matter differentiation with sulcal effacement) are consistent with anoxic brain injury due to cardiac arrest. The presence of nonreactive pupils to light stimulation following cardiac arrest carries a poor prognosis and indicates anoxic damage to the brainstem at the level of the upper midbrain. During the normal pupillary reflex, the retina as well as the optic nerve and tract transmit the light stimulus to the midbrain at the level of the superior colliculus where it is received by the pretectal nucleus and subsequently relayed to the bilateral Edinger-Westphal nuclei. These nuclei subsequently project preganglionic parasympathetic fibers through the oculomotor nerve (CN III) to the ciliary ganglion, which then projects postganglionic fibers that innervate the sphincter pupillae muscle (constricts the pupil). When light is shone in one eye, both the ipsilateral pupil (direct response) and contralateral pupil (consensual response) constrict. (Choice A) The medulla contains the glossopharyngeal (CN IX) and vagus (CN X) nerves, which provide the afferent and efferent limbs of the gag reflex, respectively. (Choice C) The occipital lobe contains the primary visual cortex. Unilateral occipital lobe damage can cause contralateral homonymous hemianopia, whereas bilateral occipital lesions may result in cortical blindness. (Choice D) The parietal lobes process and interpret visual, auditory, and motor signals received from other brain areas. Parietal lobe damage results in difficulties with spatial and visual perception. Nondominant (eg, right-sided) lesions result in hemi-neglect and constructional apraxia, whereas dominant (eg, left-sided) lesions result in Gerstmann syndrome (eg, right-left confusion, agraphia, acalculia). (Choice E) The pons contains the horizontal gaze center, which helps mediate the oculocephalic (doll's eye) reflex. It also contains the trigeminal (CN V) and facial (CN VII) nerves, which mediate the afferent and efferent limb of the corneal reflex, respectively. Bilateral pontine injury is associated with pinpoint pupils due to damage of the descending sympathetic fibers. (Choice F) Temporal lobe injury can cause disturbances in memory (eg, hippocampus), speech (eg, Wernicke area in dominant hemisphere), vision (eg, Meyer loop), and hearing (eg, primary auditory cortex). Bilateral damage to the amygdala results in Klüver-Bucy syndrome (eg, hyperphagia, hyperorality, hypersexuality). (Choice G) The thalamus is a major sensory relay station. The ventral posterolateral nucleus mediates somatic sensation of the body, the ventral posteromedial nucleus mediates facial sensation and taste, the lateral geniculate nucleus mediates vision, and the medial geniculate nucleus mediates hearing. Educational objective: The upper midbrain contains neural structures (eg, optic nerve, pretectal nuclei, Edinger-Westphal nuclei, oculomotor nerve) that mediate the direct and consensual pupillary light reflex. __________ References: The pupils. (http://www.ncbi.nlm.nih.gov/pubmed/21250222)

A 65-Year-Old Man Is Brought to the Emergency Department After