obex
{{short description|Location in the brain joining the fourth ventricle and spinal canal}}
{{for|the protocol|OBEX}}
{{Infobox brain
| 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 ({{ety|la||barrier}}) 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.{{cite journal |last1=Weerakkody |first1=Yuranga |last2=Jones |first2=Jeremy |title=Obex |website=Radiopaedia.org |date=24 March 2009 |doi=10.53347/rID-5851 |url=https://radiopaedia.org/articles/obex?lang=us |access-date=23 January 2023|doi-access=free }}
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.{{cite journal|last=Hoeffel|first=C|author2=Boukobza, M |author3=Polivka, M |author4=Lot, G |author5=Guichard, JP |author6=Lafitte, F |author7=Reizine, D |author8= Merland, JJ |title=MR manifestations of subependymomas|journal=American Journal of Neuroradiology|date=Nov–Dec 1995|volume=16|issue=10|pages=2121–9|pmid=8585504|pmc=8337222}} Hemangioblastoma has been observed in this location.{{cite journal |vauthors=Pavesi G, Berlucchi S, Feletti A, Opocher G, Scienza R |title=Hemangioblastoma of the obex mimicking anorexia nervosa |journal=Neurology |volume=67 |issue=1 |pages=178–9 |date=July 2006 |pmid=16832109 |doi=10.1212/01.wnl.0000223354.86636.ed |s2cid=24386601 |hdl=11380/1168534 |hdl-access=free }}
{{clarify span|Neurological surgical intervention in the treatment of syringomyelia or hydromyelia may involve plugging the obex to prevent the transmission of cerebrospinal fluid to the central canal of the spinal cord. Gardner suggested plugging of obex with muscle prevents transmission of CSF wave into central canal.|date=April 2016}}{{citation needed|date=April 2016}}
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.{{cite journal |pmid=25387112 |year=2015 |last1=Haley |first1=N. J. |title=Chronic wasting disease of cervids: Current knowledge and future perspectives |journal=Annual Review of Animal Biosciences |volume=3 |pages=305–25 |last2=Hoover |first2=E. A. |doi=10.1146/annurev-animal-022114-111001 }}
Additional images
File:Slide2PITER.JPG|Fourth ventricle. Posterior view. Deep dissection.
References
{{Reflist}}
{{Medulla}}
{{Ventricular system}}
{{Authority control}}