Obex
Location in the brain joining the fourth ventricle and spinal canal
title: "Obex" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["ventricular-system", "medulla-oblongata"] description: "Location in the brain joining the fourth ventricle and spinal canal" topic_path: "general/ventricular-system" source: "https://en.wikipedia.org/wiki/Obex" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0
::summary Location in the brain joining the fourth ventricle and spinal canal ::
::data[format=table title="Infobox brain"]
| Field | Value |
|---|---|
| Name | Obex |
| Latin | obex |
| Image | Gray649.png |
| Caption | Hind-brain of a human embryo of three months—viewed from behind and partly from left side. |
| Image2 | Gray709.png |
| Caption2 | Rhomboid fossa. |
| :: |
| Name = Obex | Latin = obex | Image = Gray649.png | Caption = Hind-brain of a human embryo of three months—viewed from behind and partly from left side. | Image2 = Gray709.png | Caption2 = Rhomboid fossa. | IsPartOf = | Components = | Artery = | Vein =
The obex (), also known as calamus scriptorius, is the point in the human brain at which the fourth ventricle narrows to become the central canal of the spinal cord. Cerebrospinal fluid can flow from the fourth ventricle into the obex. In anatomical studies, the obex has been found to occur approximately 10–12 mm above the level of the foramen magnum. In patients with low tonsillar position, the obex has been found at or below the plane of the foramen magnum.
The obex occurs in the caudal medulla.
The decussation of sensory fibers happens at this point.
Clinical significance
Lesions at the location can result in obstructive hydrocephalus. The most common lesion at this location is a subependymoma, a benign tumor. Hemangioblastoma has been observed in this location.
Detection of prions
Immunohistochemistry (IHC) to test brain, lymph, and neuroendocrine tissues for the presence of the abnormal prion protein to diagnose wasting diseases like chronic wasting disease in deer. Positive IHC findings in the obex is considered the gold standard.
Additional images
File:Slide2PITER.JPG|Fourth ventricle. Posterior view. Deep dissection.
References
References
- (24 March 2009). "Obex".
- Hoeffel, C. (Nov–Dec 1995). "MR manifestations of subependymomas". American Journal of Neuroradiology.
- (July 2006). "Hemangioblastoma of the obex mimicking anorexia nervosa". Neurology.
- (2015). "Chronic wasting disease of cervids: Current knowledge and future perspectives". Annual Review of Animal Biosciences.
::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::