The obex () is the point in the
human brain
The human brain is the central organ (anatomy), organ of the nervous system, and with the spinal cord, comprises the central nervous system. It consists of the cerebrum, the brainstem and the cerebellum. The brain controls most of the activi ...
at which the
fourth ventricle narrows to become the
central canal of the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
. 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
A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
.
has been observed in this location.
Detection of prions
Immunohistochemistry
Immunohistochemistry is a form of immunostaining. It involves the process of selectively identifying antigens in cells and tissue, by exploiting the principle of Antibody, antibodies binding specifically to antigens in biological tissues. Alber ...
(IHC) to test
brain
The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...
,
lymph, and neuroendocrine tissues for the presence of the abnormal
prion
A prion () is a Proteinopathy, misfolded protein that induces misfolding in normal variants of the same protein, leading to cellular death. Prions are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), w ...
protein to diagnose wasting diseases like
chronic wasting disease in
deer
A deer (: deer) or true deer is a hoofed ruminant ungulate of the family Cervidae (informally the deer family). Cervidae is divided into subfamilies Cervinae (which includes, among others, muntjac, elk (wapiti), red deer, and fallow deer) ...
. Positive IHC findings in the obex is considered the gold standard.
Additional images
File:Slide2PITER.JPG, Fourth ventricle. Posterior view. Deep dissection.
References
{{Authority control
Ventricular system
Medulla oblongata