View source for Obex

{{short description|Location in the brain joining the fourth ventricle and spinal canal}}
{{for|the protocol|OBject EXchange}}
{{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 [[Cerebellar tonsil|tonsil]]lar position, the obex has been found at or below the plane of the [[foramen magnum]].<ref>{{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 }}</ref>

The obex occurs in the [[Anatomical terms of location|caudal]] [[medulla oblongata|medulla]].

The [[Sensory decussation|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]].<ref name="pmid8585504">{{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}}</ref> [[Hemangioblastoma]] has been observed in this location.<ref name="pmid16832109">{{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 }}</ref>
{{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.<ref name=2015rev>{{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 }}</ref>

==Additional images==
<gallery>
File:Slide2PITER.JPG|Fourth ventricle. Posterior view. Deep dissection.
</gallery>

==References==
{{Reflist}}

{{Medulla}}
{{Ventricular system}}
{{Authority control}}

[[Category:Ventricular system]]
[[Category:Medulla oblongata]]