Arachnoid Cyst

Arachnoid cysts are comprised of a collection of cerebrospinal fluid located between one of the three membranes that cover the brain and the spinal cord and can be categorized as a primary arachnoid cyst or a secondary arachnoid cyst.

Primary arachnoid cysts are congenital and present at the time of birth, resulting from developmental abnormalities in the first few weeks of gestation. Secondary arachnoid cysts are a result of a head injury, tumor, meningitis, or as a brain surgical complication. Most people with primary arachnoid cysts exhibit symptoms by the age of 20 years old; however, it is not uncommon for arachnoid cysts to be asymptomatic. 

Arachnoid cysts are four times more common in males than females and generally are located outside of the temporal lobe in the middle cranial fossa. Rare cases of arachnoid cysts involve the spinal cord. 


Like most brain tumors and brain masses or cysts, symptoms depend on both the size of the cyst and the location of the cyst. Small arachnoid cysts are typically asymptomatic and often go undiscovered. Large arachnoid cysts can cause both physical and neurological symptoms. Some physical symptoms of an arachnoid cyst include macrocephaly or enlargement of the head as well as hydrocephalus or excessive cerebrospinal fluid in the brain - both in the initial stages of a primary cyst. Neurological symptoms of an arachnoid cyst include seizures, headaches, nausea and/or vomiting, hearing or vision disturbances, vertigo and difficulty with balance and walking. Less common symptoms can include hemiparesis and ataxia.


Diagnosis of arachnoid cysts generally involve CT or MRI scans of the brain or spine. The best option for these include diffusion-weighting to be able to distinguish a fluid filled arachnoid cysts for another kind of solid cyst. Many times, an arachnoid cyst is diagnosed incidentally over the course of diagnosing another symptom. 


Surgical treatments for an arachnoid cyst are extremely debatable. The general accepted rule though, is that if the arachnoid cyst is small and asymptomatic the best treatment is to monitor it over time. If, however, there are symptoms associated with an arachnoid cyst, than surgical intervention may be a plausible option. 

The goal of surgical treatment is to generally drain the cyst, instead of a full extraction, since it is much less disruptive to the surrounding brain tissue. This can be achieved with even greater results through endoscopic and microneurosurgical minimally invasive techniques. Some of these surgical options include a cystoperitoneal shunt and stereotactic cyst aspiration. 


The prognosis of arachnoid cysts is very good after treatment. Signs and symptoms tend to resolve although recurrences do occur in primary arachnoid cysts. If left untreated, a symptomatic arachnoid cyst may cause permanently severe neurological damage.   

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