This patient's nausea is a result of stimulation of the chemoreceptor trigger zone (CTZ) in the area postrema, a medullary structure that detects toxins (e.g. chemotherapeutics) in the blood and induces vomiting.
The area postrema is a small structure located on the dorsal surface of the medulla oblongata at the caudal end of the fourth ventricle. It is a highly vascular structure, and unlike the other neural structures, it lacks the characteristic tight junctions between endothelial cells. This allows the structure to sense toxins in the blood and trigger vomiting when concentrations of such toxins are high. The specific region within the area postrema that is involved in nausea and vomiting production is called the chemoreceptor trigger zone (CTZ).
Scorza et al. review the evaluation of nausea and vomiting. A comprehensive history and physical exam can typically reveal the cause of nausea and vomiting. Acute symptoms are typically the result of infectious, inflammatory or iatrogenic causes. In the evaluation process, attention should first focus on detecting emergencies or complications that require hospitalization, before proceeding with the rest of the evaluation.
Miller and Leslie review the area postrema. They describe its location and note that the area postrema along with the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus nerve make up the “dorsal vagal complex”. They note that the area postrema is not essential for motion induced vomiting, and that its projections to the NTS are likely the beginning of the efferent pathway that results in emesis.
Illustration A is a diagram of inputs that lead to vomiting as well as the sites of action of anti-emetic drugs.
Answer 2: The medial geniculate nucleus is a thalamic structure that projects to the auditory cortex of the temporal lobe and is involved in the processing of auditory information.
Answer 3: The lateral geniculate nucleus is a thalamic structure that projects to the calcarine sulcus and is involved in the processing of vision.
Answer 4: The posterior hypothalamus is responsible for the body's ability to warm itself via sympathetic output.
Answer 5: The ventral posterolateral nucleus is a thalamic structure that projects to the primary somatosensory cortex and is involved in the processing of sensation (pain, temperature, pressure, touch, vibration, and proprioception).
Scorza K, Williams A, Phillips JD, Shaw J. Evaluation of nausea and vomiting. Am Fam Physician. 2007 Jul 1;76(1):76-84. Review. PubMed PMID: 17668843.
PMID:17668843 (Link to Abstract)
Miller AD, Leslie RA. The area postrema and vomiting. Front Neuroendocrinol. 1994 Dec;15(4):301-20. Review. PubMed PMID: 7895890.
PMID:7895890 (Link to Abstract)
USMLE World Step 1 QBank Question #1741. Copyright © USMLEWorld, LLC 2012