A dorsal brainstem lesion including the area postrema in neuromyelitis optica spectrum disorder. Sagittal T2-weighted short-inversion-time recovery image shows a lesion involving the dorsal medulla oblongata extending into the upper cervical spinal cord.
Miki Y. Magnetic resonance imaging diagnosis of demyelinating diseases: An update. Clinical and Experimental Neuroimmunology. 2019;10(S1):32-48. doi:10.1111/cen3.12501
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The area postrema (AP) is a circumventricular organ (CVO) located in the dorsal medulla oblongata, at the caudal end of the fourth ventricle.
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It functions as a chemoreceptor trigger zone (CTZ) — detecting toxins in the blood and cerebrospinal fluid (CSF) — and plays a critical role in the vomiting reflex.
It is a unique region of the brainstem lacking a blood–brain barrier (BBB), allowing it to directly sense circulating substances.
| Feature | Description |
|---|---|
| Location | Dorsomedial medulla oblongata, on the floor of the fourth ventricle, at the caudal end near the obex |
| Relations | - Medially: Floor of fourth ventricle (obex region) |
The area postrema is one of the circumventricular organs, alongside:
All CVOs share the absence of a blood–brain barrier.
Primary functions of the area postrema:
| Chemoreceptor trigger zone for vomiting | • Detects emetogenic toxins, drugs, and metabolic products in blood/CSF. • Stimulates the nucleus tractus solitarius (NTS) and vomiting center in the medulla. | | --- | --- | | Autonomic and cardiovascular regulation | Modulates sympathetic/parasympathetic tone. | | Neuroendocrine integration | Responds to circulating hormones such as angiotensin II and vasopressin. | | Homeostatic functions | Involved in fluid balance, glucose regulation, and stress response. |