Arachnoid cysts are lakes of cerebrospinal fluid that have become trapped between arachnoid membranes.
Cerebrospinal fluid is a sugar-rich fluid produced in the brain and found in, around and around the spinal cord. It is produced and absorbed continuously, so that it circulates through the “subarachnoid spaces” freely and in equilibrium.
The arachnoid is one of the membranes enveloping the brain (meninges). It is a very thin veil and can sometimes form loculations that fill with cerebrospinal fluid, constituting arachnoid cysts.
Diagnosis of arachnoid cysts
About 1% of children and adults have arachnoid cysts. Most often they are discovered by chance during a cranial CT scan or brain magnetic resonance imaging (MRI) for another reason and, on very rare occasions, they may be discovered due to headache or other even less frequent symptoms.
Arachnoid cysts can be found in any brain location and less frequently in the spinal cord. The most frequent location is in the left temporal lobe.
Treatment of arachnoid cysts
In most cases they do not require any type of treatment and should only be followed up, but in exceptional cases, when symptomatic, treatment is surgical.
Endoscopic fenestration of the cyst is the treatment of choice. It consists of communicating the contents of the cyst with other subarachnoid spaces with the aid of the neuroendoscope. When this is not possible, fenestration through a craniotomy can be performed and if this fails, a valve can be implanted.
The pediatric neurosurgeon will evaluate the case and decide if, as in most cases, only periodic follow-up is necessary or if, on the contrary, surgical intervention is required, which is exceptional.