Arachnoidalzotten

Arachnoidalzotten, also known as arachnoid granulations or arachnoid villi, are small protrusions of the arachnoid mater that extend into the dural venous sinuses, most prominently the superior sagittal sinus. They facilitate the drainage of cerebrospinal fluid (CSF) from the subarachnoid space into the venous bloodstream, contributing to CSF absorption in the venous system. Their size and number vary between individuals and tend to increase with age.

Anatomically, arachnoidalzotten consist of a stalk or villus of arachnoid tissue that penetrates the sinus and is lined by arachnoid cells, with a core that may contain connective tissue and small vessels. They are separated from the blood in the sinus by the endothelial lining of the sinus wall. The granulations are most numerous along major sinuses but can be present in others such as the transverse and straight sinuses. They are detectable from birth and often enlarge or calcify with age.

Clinical significance is usually related to CSF dynamics. When CSF absorption is impaired or granulations become enlarged or calcified, they can be associated with hydrocephalus in rare cases (typically communicating hydrocephalus). On imaging, prominent arachnoidalzotten can appear as calcifications along the venous sinuses or as filling defects within the sinuses on contrast studies, and they may be mistaken for other pathologies such as thrombosis or neoplasms. They are frequently incidental findings and require correlation with symptoms and other imaging.

Radiologically, calcified granulations show hyperdensity on CT. On MRI, they may display CSF-like signals and appear as nodular prominences within the venous sinuses on appropriate sequences; their appearance can vary with imaging technique.