Arachnoid cysts are collections in the brain of cerebrospinal fluid (CSF) surrounded by a thin, transparent membrane. Some arachnoid cysts are small, incidental findings and cause no symptoms. Small arachnoid cysts often do not enlarge over time and the majority never require intervention. Others can grow and cause a variety of problems, depending on their location in the brain. Symptoms can occur at any age but are most common in childhood.
The causes of arachnoid cysts are unknown. The most common presenting symptom is headache. Children may also have seizures, hearing or visual problems, vertigo, or difficulty with balance or walking. Symptoms typically depend on the cyst size and its specific location within the brain. Large cysts may cause a condition called hydrocephalus, which is increased pressure in the brain from the obstruction of normal fluid pathways.
Arachnoid cysts are diagnosed on CT or MRI scans. These imaging studies demonstrate a collection of fluid surrounded by a cyst membrane.
The majority of arachnoid cysts require no intervention. Surgery is reserved for children with arachnoid cysts that are growing or clearly symptomatic. A variety of treatments exist, depending on the size and location of the cyst:
Shunting: One treatment option is to place a shunt, which diverts excess fluid from the cyst into the abdomen or another location. Shunts, however, can have many complications, including malfunction and infection. For this reason, neurosurgeons affiliated with Children’s Memorial Hermann Hospital prefer to perform minimally invasive endoscopic procedures to treat arachnoid cysts, whenever possible.
Endoscopic fenestration: When possible, this is the preferred treatment for patients with symptomatic arachnoid cysts. An endoscope, a small camera with working ports, is inserted through a small incision. The endoscope is used to make holes in the cyst and “communicate” the cyst (i.e., open connecting passages) to adjacent areas. This procedure prevents the cyst from expanding and may cause it to shrink.
Craniotomy for fenestration: Some symptomatic arachnoid cysts are not amenable to endoscopic fenestration and require treatment using a more invasive surgical procedure. A piece of bone from the skull is removed. The cyst is fenestrated (opened) under a high-power operating microscope, after which the bone replaced.
The majority of patients have excellent outcomes after surgical treatment of arachnoid cysts. Close follow-up is advised, and a follow-up plan will be outlined by the child’s pediatric neurosurgeon.
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