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​Arachnoid Cyst

Arachnoid cysts are fluid-filled sacs that develop between the brain or spinal cord and the arachnoid membrane. These are the most common type of brain cyst.

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What is Arachnoid Cyst?

Arachnoid cysts are cerebrospinal fluid covered by arachnoidal cells. They develop at the base of the skull, the surface of the brain, or on the arachnoid membrane. In rare cases, arachnoid cysts may also form on the spinal cord.

Arachnoid cysts usually are located in the skull, brain, and rarely, in the spinal cord.

The arachnoid cysts can grow to a large size if they continue to retain cerebrospinal fluid. In more extreme cases the cysts' size may cause the head to change shape or may displace the surrounding lobes of the brain.

Three different membranes make up the protective covering that envelops the central nervous system (the meninges). These layers, beginning with the most external, are the:

  • Dura mater
  • Arachnoid mater
  • Pia mater

Cerebrospinal fluid is mainly contained between the arachnoid layer and pia mater. An arachnoid cyst forms when the layers of the arachnoid membrane split apart and become filled with cerebrospinal fluid.

Common symptoms of arachnoid cysts include:

  • Headaches
  • Nausea
  • Vomiting
  • Balance issues

Treating arachnoid cysts

The preferred surgical treatment at UPMC for arachnoid cysts is through small openings at the side of the skull. Doctors open (fenestrate) the cyst with the help of endoscopes in this minimally invasive procedure.

At UPMC, the preferred surgical treatment for certain arachnoid cysts of the skull base is the Endoscopic Endonasal Approach (EEA). This innovative, minimally invasive treatment technique uses the nose and nasal cavities as natural corridors to access hard-to-reach or previously inoperable tumors.

Benefits of EEA include:

  • No incisions to heal
  • No disfigurement
  • Faster recovery time

Diagnosing an Arachnoid Cyst

To diagnose an arachnoid cyst, your doctor may ask you about any symptoms you're experiencing, perform a physical exam, and order imaging tests.

Symptoms of arachnoid cysts

Symptoms depend on the size and location of the cyst. Very small cysts may not cause any symptoms at all and may be discovered during an unrelated exam.

Larger sized arachnoid cysts can cause a variety of neurologic symptoms, including:

  • Headache
  • Nausea and vomiting
  • Seizures
  • Hearing and visual disturbances
  • Balance problems
  • Hydrocephalus (enlargement of the head due to accumulation of cerebrospinal fluid)

Imaging tests for diagnosing arachnoid cysts

Doctors usually identify larger cysts with symptoms by imaging studies as part of a neurologic exam.

MRI is the preferred technique because these scans can reveal fluid-filled cysts as distinct from other types of cysts.

Arachnoid Cyst Treatment

Some doctors prefer to treat only symptomatic arachnoid cysts. Others advocate treatment for asymptomatic cysts to prevent the possibility of future damage.

Within these groups, some doctors focus their treatment on alleviation of the symptoms, while others recommend surgery.

Surgery for arachnoid cysts

The goals of surgery are to drain the cyst and prevent it from refilling.

To prevent the cyst from refilling, doctors remove the outer membrane of the cyst or open a small window on the cyst (fenestrating the capsule) to create wide communications with the normal surrounding subarachnoid space.

Certain arachnoid cysts of the skull base, such as sellar and suprasellar cysts, can be accessed directly using the Endoscopic Endonasal Approach (EEA).

This state-of-the-art, minimally invasive treatment approach allows surgeons to access the tumor through the natural corridor of the nose, without making an open incision. Surgeons then remove the cyst through the nose and nasal cavities.

EEA surgery offers the benefits of no incisions to heal, no disfigurement, and a faster recovery time.