Obex

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Brain: Obex
Hind-brain of a human embryo of three months—viewed from behind and partly from left side.
Rhomboid fossa.
Latin	Obex
Gray's	p.797
NeuroNames	hier-633
NeuroLex ID	nlx_151877

The obex (from the Latin for barrier) is the point in the human brain at which the fourth ventricle narrows to become the central canal of the spinal cord.

The obex occurs in the caudal medulla.

The decussating 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.^[1] Hemangioblastoma has been observed in this location.^[2] 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.

Additional images

Fourth ventricle. Posterior view.Deep dissection.

References

↑ Hoeffel, C; Boukobza, M; Polivka, M; Lot, G; Guichard, JP; Lafitte, F; Reizine, D; Merland, JJ (1995 Nov-Dec). "MR manifestations of subependymomas.". AJNR. American journal of neuroradiology 16 (10): 2121–9. PMID 8585504. Check date values in: |date= (help)
↑ Pavesi G, Berlucchi S, Feletti A, Opocher G, Scienza R (July 2006). "Hemangioblastoma of the obex mimicking anorexia nervosa". Neurology 67 (1): 178–9. doi:10.1212/01.wnl.0000223354.86636.ed. PMID 16832109.

Human brain: rhombencephalon, myelencephalon: medulla (TA A14.1.04, GA 9.767)

Dorsal

Surface

Grey: Cranial nuclei

afferent:	GVA: VII,IX,X: Solitary/tract/Dorsal respiratory group SVA: Gustatory nucleus GSA: VIII-v Lateral Medial Inferior

efferent:	GSE: XII GVE: IX,X,XI: Ambiguus SVE: X: Dorsal IX: Inferior salivatory nucleus

Grey: other

White: Sensory/ascending

White: Motor/descending

Ventral

White: Motor/descending	Motor decussation Olivocerebellar tract Rubro-olivary tract

Grey matter	Ventral respiratory group Arcuate nucleus of medulla Inferior olivary nucleus Rostral ventromedial medulla

Surface	Anterior median fissure Anterolateral sulcus Olive Pyramid

Grey: Raphe/
reticular

M: CNS

anat (n/s/m/p/4/e/b/d/c/a/f/l/g)/phys/devp

noco (m/d/e/h/v/s)/cong/tumr, sysi/epon, injr

proc, drug (N1A/2AB/C/3/4/7A/B/C/D)

Ventricular system, rhombencephalon, met- and myel-: fourth ventricle (TA A14.1.05.701–726, GA 9.797)

Roof (dorsal)

rostral:	Superior medullary velum (Frenulum)

caudal:	Inferior medullary velum Taenia of fourth ventricle

Floor/rhomboid fossa (ventral)

rostral (pons):	Facial colliculus Locus coeruleus

caudal (medulla}:	Vagal trigone Hypoglossal trigone Area postrema Obex

Medial eminence Sulcus limitans

Apertures

Other

M: CNS

anat (n/s/m/p/4/e/b/d/c/a/f/l/g)/phys/devp

noco (m/d/e/h/v/s)/cong/tumr, sysi/epon, injr

proc, drug (N1A/2AB/C/3/4/7A/B/C/D)

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