Meningeal Cyst
A meningeal cyst is a fluid-filled sac that develops in association with the meninges, the protective membranes that surround the brain, spinal cord, and nerve roots. In the spine, meningeal cysts may form inside the spinal canal, along the nerve roots, or just outside the dura. They typically contain cerebrospinal fluid and are most often discovered incidentally on MRI. The vast majority cause no symptoms, but larger cysts can occasionally compress nearby nerves or the spinal cord and produce pain, numbness, weakness, or other neurological symptoms.
What is it?
The meninges are three protective membranes that surround the brain, spinal cord, and nerve roots: the dura, the arachnoid, and the pia. A meningeal cyst is a fluid-filled lesion that develops from or in close relationship with these membranes. Most meningeal cysts of the spine contain cerebrospinal fluid (CSF), the same fluid that normally bathes the brain and spinal cord, and many communicate with the larger CSF spaces.
Spinal meningeal cysts are typically classified into three main groups. Type I cysts are extradural (outside the dura) and do not contain nerve roots; these include arachnoid cysts and sacral meningoceles. Type II cysts are extradural and contain nerve roots; the most common example is the Tarlov, or perineural, cyst, which forms along a nerve root sleeve, most often in the sacrum. Type III cysts are intradural (inside the dura), such as intradural arachnoid cysts, which can occur along the spinal cord in the thoracic and other regions. This classification helps guide imaging interpretation and treatment.
The cause of most meningeal cysts is not fully understood, but the majority appear to be congenital or developmental, related to subtle variations in how the meninges form. Some may enlarge slowly over time. Less commonly, meningeal cysts can develop after trauma, prior surgery, lumbar puncture, infection, or inflammation. Risk factors include certain connective tissue disorders, although most patients have no specific underlying condition.
The vast majority of meningeal cysts cause no symptoms and are discovered incidentally on MRI of the spine performed for other reasons. When symptoms do occur, they depend on the cyst’s size, location, and effect on surrounding structures. Possible symptoms include localized back pain; radiating pain into the arms, legs, buttocks, or pelvis; numbness or tingling; weakness; gait or balance difficulty; and, in some cases, bowel, bladder, or sexual dysfunction. Symptoms may worsen with activities that increase CSF pressure, such as coughing, sneezing, or straining. Importantly, many people with meningeal cysts have separate causes for their back or limb pain, so determining whether the cyst is responsible for symptoms requires careful evaluation.
MRI of the spine is the preferred imaging test for identifying and characterizing meningeal cysts because it provides detailed views of the cyst’s contents, its relationship to the dura and nerve roots, and any associated bone changes such as scalloping of adjacent vertebrae. CT and CT myelography may be used in selected cases when MRI is contraindicated or when more detailed information about cyst communication with the CSF space is needed.
Important to Know
For most people, a meningeal cyst is an incidental MRI finding that does not require treatment, activity restriction, or follow-up imaging. When symptoms are present, the first step is determining whether they are actually caused by the cyst or by another, more common condition. Conservative care for any associated discomfort may include physical therapy, posture and ergonomic adjustments, activity modification, and pain management. For carefully selected patients with persistent, debilitating symptoms clearly attributable to a meningeal cyst, image-guided procedures such as cyst aspiration or fibrin glue injection, or surgical treatment, may be considered. These interventions can be helpful in some patients but carry their own risks, including CSF leak, infection, recurrence, or new neurological symptoms, so they are generally reserved for severe cases and performed in specialized centers.
Because meningeal cysts are common and most are asymptomatic, accurate recognition on imaging helps avoid unnecessary procedures while ensuring that genuinely symptomatic cysts are not overlooked. Imaging findings are always interpreted together with the patient’s symptoms and overall clinical picture.
Red flag symptoms include sudden severe back, leg, or pelvic pain; rapidly progressive leg weakness or numbness; new saddle-area numbness; new bowel or bladder dysfunction; fever or chills with back pain; or unexplained weight loss. These warrant prompt medical evaluation, as they may indicate cauda equina syndrome, infection, or another serious underlying condition rather than a simple meningeal cyst.