Arachnoid cysts are fluid-filled pouches that form between the leaves of the arachnoid membrane, which is one of the membranes surrounding the brain and the spinal cord. The brain has different types of membranes which are called dura mater, arachnoid and pia mater respectively from outside in. Although arachnoid cysts are arachnoids, they usually expand inward. They are most commonly found around the temporal lobe of the brain. They can also be seen in the thalamocoele, suprasellar region, cerebellum and the brain stem. The main reason for its occurrence is unknown. Arachnoid cysts rarely develop due to trauma, tumor, infection or neurosurgery.
In many cases, the arachnoid cyst is congenital, but may not even show any symptoms throughout the patient’s lifetime. When there are symptoms however, they may vary depending on the size of the cyst and the brain region in which it is located. Symptoms usually begin during childhood.
The most common symptoms are nonspecific headache, vomiting, nausea and dizziness. These often are caused by the increase in intra-cranial pressure due to hydrocephalus. Sometimes it can also cause abnormal expansion of skull bones in children. Apart from that, epileptic seizures, weakness, visual defects and hearing defects may also occur. Movement disorders and retarded development may be observed. It can be the cause of weakness (paralysis) in one half of the body. If it is pressuring on hormone-secreting parts of the brain, it can create hormonal irregularities, developmental defects and sexual disorders.
If arachnoid cysts form in the spine and spinal cord (spinal arachnoid cyst), they can cause loss of sensation and loss of strength (paralysis) in the arms, hands, legs. They can also cause scoliosis, back/lower back pain and spasticity.
It does not cause any symptoms in many of the cases. In cases with symptoms, headaches, seizures may occur. The diagnosis is made by magnetic resonance (MRI) imaging or computed tomography (CT). Sometimes, cerebrospinal fluid in the head can block the circulatory pathways, causing an increase in cerebrospinal fluid in the brain (hydrocephalus).
Many arachnoid cysts are found incidentally in MRI and CT images and usually do not grow in follow-ups. Most of them are not even followed up as they do not cause any symptoms in the individuals. When symptoms appear, the size of the cyst, the brain region in which it formed are re-evaluated according to the pathology it creates.
In surgical treatment, ventriculoperitoneal shunt operations are considered with open craniotomy and fenestration. In open craniotomy and fenestration, the cyst is reached by making an opening on the skull bones. Many openings are created on the cyst wall. Thus, cerebrospinal fluid in the cyst content can be discharged into the subarachnoid space and absorbed like cerebrospinal fluid circulating around the brain as usual. In some cases, a tube (shunt catheter) inserted into the cyst can be inserted into the abdominal cavity, draining the contents of the cyst. Endoscopic cyst fenestration is also possible.
Cysts around the spinal cord are usually completely removed. This way, most of the symptoms are eliminated. In cases where the entire cyst cannot be removed, an anastomotic link is created between the cyst and the subarachnoid space, or the cyst contents are drained by a shunt.
