WHAT IS AN ARACHNOID CYST ? MELBOURNE …

1 WHAT IS AN ARACHNOID cyst ?The Brain is covered with membrane that is calledARACHNOID (called this because it looks like the web ofa spider). In between these layers there is fluid that bathesthe brain called cerebrospinal fluid( ). This membraneeither duplicates or splits to form a fluid filled space calledan ARACHNOID DO THEY FORM ?They are developmental (they are the result of changes thatoccur while the baby forms in the womb).IN WHAT PARTS OF THE BRAINDO THEY OCCUR ?The commonest location is in the area called the sylvianfissure (as shown in the picture and Xray) Otherwise theyusually occur on the surface of the brain or where the DO THEY AFFECT YOU ?This depends on which part of the brain they commonly cause no problems at all and may be foundon a CAT scan or MRI scan done for other they become large in size they may push on the surround-ing structures and prevent them working.

2 This may producestroke like they cause they may be the cause of fitting (seizures).If a blood vessel crosses the cyst this may bleed and causecollapse. A small injury to the brain may cause this and atother times it may be scan of BrainshowingRight Sylvian ARACHNOID cyst (dark area on left of picture)Section of brainshowingRight Sylvian ARACHNOID cyst (blue area on left of picture) This brochure is copyright. No part of it may be repro-duced in any form without prior permission from the brochure is to provide general informa-tion and does not replace a consultation with your I have a cyst diagnosed do I need regular CT scans to check on it ? NEUROSURGERY PTY LTDACN 082 289 316 PHONE 03 9816 - 9844 FACSIMILE 03 9816 - 9877545 ROYAL PARADEPARKVILLE VIC 3052IS SURGERY ALWAYS NEEDED ?

3 The initial procedure is called a craniotomy and internaldrainage. This involves the removal of a piece of bone fromthe skull to allow access to the cyst . Using a microscope asmall hole is placed in the deep part of the cyst to allow thefluid from around the brain to wash in and out. This takesthe pressure off and usually the cyst will shink in the cyst will not reduce much and this isbecause the cyst has been present for a long the above does not work then the cyst may have a catheterinserted between it and the fluid in the rest of the brain ordown to the abdomen under the skin. (called a SHUNT )NOMostly the cysts are observed but if they are causingsymptoms surgery is usually this may be recommended, particularly if thecyst had been felt to to be the cause of some symptoms andsurgery was not felt to be needed the cyst had been found accidentally and we felt that itwas unlikely to cause any problems then we would followyou up based only on the developement of new the ARACHNOID cyst get bigger ?

4 YESIf it does grow it is usually at a small rate. Theconcern may be in very large cysts that they may block thenormal flow of CSF around or through the brain. Irf this isfelt to be the case surgery may be offered to prevent the cystcausing any problems in the ARACHNOID cysts inherited ?Not as far as we know at this ARACHNOID cysts a type of tumour ?NoThey are formed from normal body IS THIS DIAGNOSED ?CAT SCANThis is usually the first test. This is a computerisedX-ray of your brain and this shows the fluid as a darkarea.(see pic) (Magnetic Resonance Imaging)This is the next test. It produces pictures like theCAT scan but they are generated using a magnetic field andnot using radiation.

5 This test is not always needed if theCAT scan shows the problem. This may be used to confirmthat the abnormality on the CAT scan is an ARACHNOID cystbecause it sometimes can be confused for other types are referred to a specialist after the CAT scan in mostcases and they organise any further common specialists to be referred to are:NeurosurgeonsNeurologistsIn most cases nothing further will be you are having symptoms that are related to the arach-noid cyst then it may need to be treated with happens when an ARACHNOID cyst is diagnosed ?If I require surgery what will it be ?There are two types of operation that will be suggested. Thesurgeon usually decides which is required.

6 This will dependon many factors. The aim is to drain the cyst or to connectit to something it can drain can either be connected to the fluid cavities around thebase of the brain(usually the first thing tried) or drained tothe lining around the bowel in the abdomen(this is called ashunt).