About arachnoid cysts

What is arachnoid cysts?

Arachnoid cysts are fluid-filled sacs that occur on the arachnoid membrane that covers the brain (intracranial) and the spinal cord (spinal). There are three membranes covering these parts of the central nervous system: the dura mater, arachnoid, and pia mater. Arachnoid cysts appear on the arachnoid membrane, and they may also expand into the space between the pia mater and arachnoid membranes (subarachnoid space). The most common locations for intracranial arachnoid cysts are the middle fossa (near the temporal lobe), the suprasellar region (near the third ventricle) and the posterior fossa, which contains the cerebellum, pons, and medulla oblongata.

In many cases, arachnoid cysts do not cause symptoms (asymptomatic). In cases in which symptoms occur, headaches, seizures and abnormal accumulation of excessive cerebrospinal fluid in the brain (hydrocephalus) are common. The exact cause of arachnoid cysts is unknown. Arachnoid cysts are classified according to their specific location.

What are the symptoms for arachnoid cysts?

Most don't cause any problems. You may not know you have one unless your doctor is checking you for another issue, like a seizure or head injury.

Sometimes, though, a cyst gets big enough to press on your brain, spinal cord, or a cranial nerve, which can lead to a variety of symptoms. If you're going to have symptoms, they'll probably show up during childhood.

The symptoms vary from mild to severe, depending on the size and location of the cyst. They may include:

  • Headache
  • Nausea
  • Vomiting
  • Feeling tired and lethargic
  • Seizures
  • Lumps on your head or spine
  • Developmental delays in children
  • Hormonal issues like early puberty
  • Uncontrolled head bobbing
  • Vision problems
  • Fluid build-up in the brain (hydrocephaly)

Rarely, you may have Weakness or paralysis on one side of your body. This is called hemiparesis. Another rare complication in children is an enlarged head (macrocephaly).

What are the causes for arachnoid cysts?

The exact cause of arachnoid cysts is not known. Researchers believe that most cases of arachnoid cysts are developmental malformations that arise from the unexplained splitting or tearing of the arachnoid membrane. According to the medical literature, cases of arachnoid cysts have run in families (familial cases) suggesting that a genetic predisposition may play a role in the development of arachnoid cysts in some individuals.

In some cases, arachnoid cysts occurring in the middle fossa are accompanied by underdevelopment (hypoplasia) or compression of the temporal lobe. The exact role that temporal lobe abnormalities play in the development of middle fossa arachnoid cysts is unknown.

Some complications of arachnoid cysts can occur when a cyst is damaged because of minor head trauma. Trauma can cause the fluid within a cyst to leak into other areas (e.g., subarachnoid space). Blood vessels on the surface of a cyst may tear and bleed into the cyst (intracystic hemorrhage), increasing its size. If a blood vessel bleeds on the outside of a cyst, a collection of blood (hematoma) may result. In the cases of intracystic hemorrhage and hematoma, the individual may have symptoms of increased pressure within the cranium and signs of compression of nearby nerve (neural) tissue.

Arachnoid cysts can also occur secondary to other disorders such as Marfan’s syndrome, arachnoiditis, or agenesis of the corpus callosum.

What are the treatments for arachnoid cysts?

Most arachnoid cysts are found incidentally and remain constant in size, leading many physicians to recommend conservative treatment. When no symptoms are present, no treatment may be necessary and affected individuals may be periodically monitored. If symptoms arise, a cyst can be reevaluated.

When treatment is necessary the specific therapy used depends upon whether symptoms are present, the size of the cyst and the specific location of the cyst within the skull.

In cases where treatment is recommended, therapy traditionally consists of one of two procedures – an open craniotomy fenestration or ventriculoperitoneal shunting.

During a craniotomy fenestration, a portion of the skull is removed to give a surgeon access to the cyst, where multiple openings are made in the cyst wall, (fenestrations), to allow cerebrospinal fluid to drain into the subarachnoid space where the fluid is reabsorbed into the surrounding tissue. Alternatively, some cases may be treated by surgically inserting a device (shunt) into the cyst to provide drainage either into the ventricular system of the brain or into the abdominal cavity. This will drain the cyst and provide an adequate passageway for cerebrospinal fluid to circulate.

More recently, advancements in minimally invasive brain and skull base surgery have evolved these traditional procedures into fully endoscopic techniques, distinguished by shorter operating times, fewer complications, excellent outcomes with faster recovery and overall decreased patient morbidity. While the approach varies depending on the size and location of the arachnoid cyst, fully endoscopic surgical management has provided the surgeon with superior access for either fenestration, or in other cases, resection of the cyst without the complications and risks associated with brain manipulation or retraction. Few facilities provide minimally invasive, endoscope assisted fenestrations, endoscopic shunt placement and endscope assisted or fully endoscopic resection of arachnoid cysts as treatment when indicated.

Spinal arachnoid cysts may be treated by the complete surgical removal (resection) of the cyst, if possible. Surgery generally leads to a resolution of symptoms. In some cases, complete surgical removal of a spinal cyst is not possible. In such cases, fenestration or shunting of the cyst to drain the fluid may be necessary.

Other treatment is symptomatic and supportive.

What are the risk factors for arachnoid cysts?

Arachnoid cysts affect males more often than females. These cysts may occur at any age and have been found in all races and geographic locations. They are the most common type of intracranial cyst. Because many cases of arachnoid cysts have no symptoms, it is difficult to determine the true frequency of this disorder in the general population.

Is there a cure/medications for arachnoid cysts?

Most treatment is symptomatic and supportive unless the cyst requires surgery.

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