A 34-year-old man begins treatment with combination chemotherapy for Hodgkin lymphoma. Shortly thereafter, he experiences severe vomiting and requires intravenous fluid supplementation. Which of the following sites in the brain is most likely responsible for his symptoms?

Question

A 34-year-old man begins treatment with combination chemotherapy for Hodgkin lymphoma.  Shortly thereafter, he experiences severe vomiting and requires intravenous fluid supplementation.  Which of the following sites in the brain is most likely responsible for his symptoms?

Quizplus · Accepted Answer

11ec160b_35be_06d2_9249_e9d5e16b1702_MD0001_00 This patient developed acute vomiting after treatment with systemic chemotherapy. The vomiting reflex is initiated by the chemoreceptor trigger zone (CTZ, or area postrema) and nucleus tractus solitarius. The area postrema is located on the dorsal surface of the medulla at the caudal end of the fourth ventricle; this region does not have a well-developed blood-brain barrier, allowing it to be exposed to chemicals circulating in the blood. The CTZ can be triggered directly by emetogenic substances (eg, drugs, toxins) or indirectly by vagal afferents from the gastrointestinal tract. Chemotherapeutic agents (eg, cyclophosphamide) cause damage to enterocytes, resulting in release of serotonin. This stimulates 5-HT3 receptors on vagal afferent fibers located in the bowel wall, which then ascend to the CTZ to trigger the vomiting reflex. Chemotherapy-associated emetic stimuli in the cerebrospinal fluid and bloodstream also can stimulate the area postrema directly by causing local release of substance P, which activates neurokinin-1 (NK1) receptors in the brainstem to induce vomiting. (Choice A) The thalamus is superior to the midbrain and makes up part of the lateral wall of the third ventricle. It coordinates sensory and motor function, regulates sleep and wakefulness, and plays an important role in memory and cognition. (Choice B) The superior and inferior colliculi are located in the dorsal midbrain. They are involved in processing visual (superior colliculi) and auditory (inferior colliculus) information and initiating movement of the head and eyes in response to visual or auditory input. (Choice C) The ventral pons is inferior to the midbrain in the brainstem and contains the corticospinal tract (eg, limb/torso movement), corticobulbar tract (eg, face/head/neck movement), and abducens nucleus (eg, horizontal eye movement). (Choice E) The cerebellum makes up the posterior wall of the fourth ventricle and plays an important role in motor control (eg, coordination, precise movements, posture) and cognitive function (eg, attention, language). Educational objective: The vomiting reflex is initiated by the chemoreceptor trigger zone (ie, area postrema) and nucleus tractus solitarius within the dorsal medulla at the caudal end of the fourth ventricle. The area postrema does not have a well-developed blood brain barrier, allowing it to be activated directly by emetogenic substances (eg, drugs, toxins) or indirectly by ascending afferents from the bowel wall (eg, chemotherapy-induced release of serotonin). __________ References: Physiology, Chemoreceptor Trigger Zone (http://www.ncbi.nlm.nih.gov/pubmed/30725818)

A 34-Year-Old Man Begins Treatment with Combination Chemotherapy for Hodgkin