The arachnoid cyst is a neurological disorder involving fluid-filled sacs than can develop between the surface of the brain and the arachnoid membrane, one of the three membranes that protect the brain and spinal cord. Generally, cases of arachnoid cysts become apparent in infancy, but may not show up until adolescence. Symptoms are related to the size and location of the cysts. Smaller cysts may cause no harm, and are discovered during routine examinations of the head; large cysts may cause deformation of the cranial vault or macroencephaly. When either of these problems occur, the following symptoms can develop: headaches, seizures, hydrocephalus (excessive CS fluid), developmental delay, increased intercranial pressure, and hemiparesis. Less frequent symptoms can include lethargy, visual impairment, bobbing of the head. Arachnoid cysts occur most frequently in males. There is no cure, but shunts may be placed to remove pressure from the cyst.

Treatment is symptomatic; and patients will be treated according to whatever symptoms are present. If left untreated, arachnoid cysts can cause advanced neurological disorders, caused by the growth of the cyst. Moderate to severe intercranial hemorrhaging can also occur. Typically, the cyst can be spotted using traditional CT scans and MRIs. The CT scan will show a smooth cystic mass composed of a density similar to cerebrospinal fluid.

The most common operative treatments on arachnoid cysts are by needle aspiration (punching a hole in the cyst, and draining fluid), craniotomy (opening of the skull) and excision of the cyst, and shunting of the cyst. There are pros and cons to each method. For example, while needle aspiration is a fairly non-invasive method, there is a high recurrence of cysts afterward. A craniotomy is a high-cost, very invasive procedure, but it usually takes care of all the cysts. Shunts seem to be the most proven and the best overall treatment, because there is a low risk of surgery-related complications, and there is a low rate of recurrence. However, the patient becomes dependent on the shunts, having to return later for more.


Sources: http://www.ninds.nih.gov/health_and_medical/disorders/aracysts_doc.htm
http://neurosun.medsch.ucla.edu/Diagnoses/BrainTumor/BrainTumorDis_7.html

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