Left temporal arachnoid cyst
Preoperative coronal T2 CMRI
An intracranial arachnoid cyst is a congenital abnormality where cysts form in the arachnoid mater. Arachnoid cysts are benign. The cyst contains cerebrospinal fluid and consists of arachnoidal cells and collagen. Because it is not connected to the ventricular system, the contained cerebrospinal fluid is not drained, and upon secretion of CSF by the arachnoid mater the cyst increases in size. This can lead to displacement or aplasia of the adjacent brain areas. The thus increased intracranial pressure can lead to mass displacement, compression of brain areas and blood vessels and pressure erosions of the skull.
The symptoms are often nonspecific: headache, dizziness, blurred vision. Rarely neurologic deficits occur, although in children they occur more often, for example developmental delays (especially motor and language development disorders) and epileptic seizures can occur.
About 2 / 3 of arachnoid cysts are found in the middle fossa and in the posterior cranial fossa. Preferred side is left and females are about 3 times more frequently affected than men. Symptoms usually occur in childhood, youth and young adulthood. For diagnosis a CMRT with contrast medium is required. The typical result is shown in the picture: well-defined, homogeneous, cystic formation with low to moderate displacement of surrounding structures. There is no accumulation of contrast medium in the cyst wall or in internal structures of the cyst (contradictory to what is seen in tumor cysts), the signal can be liquorisointens or liquorhyperintens, depending on the protein content of the fluid. Commonly thin septae and cortical vessels are found inside the cyst (see here).
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