Arachnoid cysts usually are located in the skull, and rarely, in the spinal cord. The cysts can grow to a large size if they continue to retain cerebrospinal fluid. In more extreme cases the cysts actually may cause the head to change shape or may displace the surrounding lobes of the brain.
Three different membranes make up the meninges, a protective covering that envelops the central nervous system. These layers, beginning with the most external, are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is mainly contained between the arachnoid layer and the pia mater. An arachnoid cyst forms when the layers of the arachnoid membrane split apart and become filled with cerebrospinal fluid.
The preferred surgical treatment at UPMC for arachnoid cysts is through small openings at the side of the skull. The cyst is opened (fenestrated) with the help of endoscopes in this minimally invasive procedure.
Your doctor may ask about any symptoms you are experiencing. 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 examination. Larger cysts can cause a variety of neurologic symptoms, including:
- nausea and vomiting
- hearing and visual disturbances
- balance problems
- hydrocephalus (enlargement of the head due to accumulation of cerebrospinal fluid)
Larger cysts with symptoms usually are identified by imaging studies as part of a neurologic examination. MRI is the preferred technique, as these scans can reveal fluid-filled cysts as distinct from other types of cysts.
Some doctors prefer to treat only symptomatic arachnoid cysts, while others advocate preventive treatment for asymptomatic cysts to prevent the possibility of future damage. Within these groups, some focus their treatment on alleviation of the symptoms, while others recommend surgery.
The goals of surgery are to drain the cyst and prevent it from refilling. This second part is accomplished by removal of the outer membrane of the cyst or by opening 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 through the Endoscopic Endonasal Approach (EEA). This state-of-the-art, minimally invasive surgical procedure uses the nose as a natural corridor to reach these lesions. There are no incisions in the skin of the face or head.