Arachnoid cysts

Arachnoid cysts are benign cysts that occur in the cerebrospinal axis in relation to the arachnoid membrane and that do not communicate with the ventricular system. They usually contain clear, colorless fluid that is most likely normal cerebrospinal fluid; rarely, they contain xanthochromic fluid.

Most are developmental anomalies. A small number of arachnoid cysts are acquired, such as those occurring in association with neoplasms or those resulting from adhesions occurring in association with leptomeningitis, hemorrhage, or surgery. They constitute approximately 1% of intracranial masses; 50-60% occur in the middle cranial fossa. Cysts in the middle cranial fossa are found more frequently in males than in females; they occur predominantly on the left side. Most arise as developmental anomalies. A small number of arachnoid cysts are associated with neoplasms.

Imaging:

MRI is the diagnostic procedure of choice because of its ability to demonstrate the exact location, extent, and relationship of the arachnoid cyst to adjacent brain or spinal cord. Myelography and computed tomography (CT) myelography remain of diagnostic value, especially for cases that are not definitive on MRI.

Plain radiographic findings are nonspecific and have little to offer in the diagnosis of arachnoid cysts, although changes in skull contour may be detected on skull radiographs performed for other indications, such as trauma.Cranial ultrasonography is an important diagnostic tool during the first year of life. Although symptomatic arachnoid cysts are comparatively rare in infants, ultrasound is useful as a noninvasive imaging technique with high yield in the detection and characterization of cystic masses.Although angiography may show associated anomalies of venous drainage and the relationship of the lesion to normal vasculature, which may be useful for surgical planning, in practice, angiography is rarely performed, because CT angiography or magnetic resonance angiography provides the same information noninvasively. Every effort must be made to reliably detect arachnoid cysts, because most arachnoid cysts are an incidental finding and most patients are asymptomatic. Arachnoid cysts must be differentiated from the more serious cystic intracranial and intraspinal tumors. In cases involving larger arachnoid cysts, consideration should be given to the use of serial scans, because such cysts may enlarge over time; patients with such cysts may become candidates for surgery.Treatment for arachnoid cysts

A very simple, fast and minimally-invasive treatment is burr hole drainage of the cyst. There is a high rate of recurrence and return of symptoms

with this procedure, however.A craniotomy can also be performed to remove the cyst wall and ensure normal communication with the cerebrospinal fluid pathways. This is a more invasive procedure, but allows for direct inspection of the cyst. Another option is the minimally-invasive endoscopic fenestration of the cyst, where the physician drains the cyst with a needle.Shunting of the cyst is the simplest surgical procedure. A patient becomes dependent on the shunt, however, which can cause complications.