Arachnoid knots

Granulationes arachnoideae

Arachnoid villi

Small valve bodies by means of which cerebrospinal fluid can travel from the subarachnoid space into the blood in the upper midstical blood channel (sinus sagittalis superior) and thus leave the brain and skull cavity.
The arachnoid alknots are approx. 0.5 - 2 mm in size and often sit in dense groups connected by bulges (lacunae) from the blood channel.