arachnoid villi


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Related to arachnoid villi: hydrocephalus, choroid plexus

villus

 [vil´us] (L.)
a small vascular process or protrusion, as from the free surface of a membrane.
arachnoid villi microscopic projections of the arachnoid into some of the venous sinuses.
chorionic villi see chorionic villi.
intestinal villi multitudinous threadlike projections covering the surface of the mucous membrane lining the small intestine, serving as the sites of absorption of fluids and nutrients.
synovial villi slender projections from the surface of the synovial membrane into the cavity of a joint; called also haversian glands.

a·rach·noid vil·li

tufted prolongations of pia-arachnoid that protrude through the meningeal layer of the dura mater and have a thin limiting membrane; collections of arachnoid villus form arachnoid granulations that lie in venous lacunae at the margin of the superior sagittal sinus; the spongy tissues of the a. villus serve as one-way valves for the transfer of cerebrospinal fluid from the subarachnoid space to the venous system. Both a. villus and the granulations formed from them are major sites of fluid transfer.
See also: arachnoid granulations.

a·rach·noid vil·li

(ă-rak'noyd vil'ī)
Tufted prolongations of pia-arachnoid that protrude through the meningeal layer of the dura mater and have a thin limiting membrane; collections of arachnoid villi form arachnoid granulations that lie in venous lacunae at the margin of the superior sagittal sinus; the spongy tissue of the arachnoid villus contains tubules that serve as one-way valves for transfer of cerebrospinal fluid from the subarachnoid space to the venous system. Both arachnoid villi and the granulations formed from them are major sites of fluid transfer.
See also: arachnoid granulations
References in periodicals archive ?
Mucosal and epidermal lesions resolve with vitamin A supplementation, but it is not known whether the changes in the arachnoid villi are reversible.
Infectious processes such as meningitis can impede reabsorption of CSF at the level of the arachnoid villi resulting in hydrocephalus (Greenberg, 2001).
Pacchionian granulations are reported more frequently among adults, but earlier stages of hypertrophic arachnoid villi can be present as early as 18 months of age.
(2-6) Kumar et al (2) postulated that these tumors arise from meningoepithelial cells, which are present throughout the arachnoid membrane with more concentration at the arachnoid villi within the dural venous sinuses.
(5) Normally occurring arachnoid villi and draining veins that penetrate the skull base have also been identified as possible sites from which a skull base defect could arise.
The sinus thrombosis resulted in an increase in pressure in the superior sagittal sinus and a decrease in CSF absorption by arachnoid villi. The higher intracranial pressure was the most likely cause of the contralateral abducens palsy.