Stereomicroscopic and microscopic study showed human arachnoid granulations with different morphology that we classified in simple and lobate. Simple granulations were small and completely involved by fibrous capsule that delimited a continuous subdural space from the pedicle to the apex. Lobate granulations were bigger than the simple; in the apex the fibrous capsule was thinner than in other regions, and fused with granulation periphery causing interruption of subdural space. Simple granulations might be an initial development stage; lobate granulations would represent a higher development stage, with ideal morphologic structure for absorption of the CSR.
arachnoid granulations; development; classification