Head and Neck Imaging

Arachnoidal granulation

tufted extensions of piaarachnoid, composed of arachnoid villi that penetrate dural venous sinuses, providing the primary mechanism for cerebrospinal fluid resorption into the intracranial venous system. Aberrant arachnoidal granulations may be located in the dural surfaces of the temporal bone, or the dural surfaces of the ethmoid and sphenoid sinus air cells. Progressive enlargement of these aberrant structures with increasing age and spinal fluid pressure fluctuations may cause bone erosion of the adjacent cavities. This possibly leads to spontaneous adult cerebrospinal fluid otorrhoea or rhinorrhoea by the communication of the subarachnoidal space with the otomastoid, ethmoid or sphenoid air cells. Such an enlarged aberrant arachnoidal granulation may be seen on CT as a focal bone defect communicating with an air cell. Also, see cerebrospinal fluid leak.

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