Tarlov Cyst
A Tarlov cyst, also called a perineural cyst, is a fluid-filled sac that forms along the sheath of a spinal nerve root, most often in the sacrum at the base of the spine. Tarlov cysts contain cerebrospinal fluid and are usually discovered incidentally on MRI performed for other reasons. The vast majority cause no symptoms. In a small number of cases, a larger cyst can compress nearby nerves and produce lower back, buttock, leg, or pelvic symptoms.
What is it?
A Tarlov cyst, also known as a perineural cyst or sacral nerve root cyst, is a fluid-filled sac that develops between the protective layers covering a spinal nerve root. The cyst is in continuity with the cerebrospinal fluid (CSF) space, meaning the fluid inside it is the same fluid that surrounds the brain and spinal cord. Tarlov cysts most commonly form along the sacral nerve roots at the base of the spine, but they can occur at other levels as well. They were first described by neurosurgeon Isadore Tarlov in the 1930s, and they are now most often identified on MRI.
The exact reason Tarlov cysts develop is not fully understood. Most are thought to be congenital or developmental, possibly related to subtle variations in the way the nerve root sheaths form, with CSF gradually working its way into a small outpouching. They tend to be more common in women and in adults, and may slowly enlarge over time. In some cases, trauma, prior lumbar puncture, or inflammation has been suggested as a contributing factor, though for most patients no clear precipitating event is identified. Tarlov cysts are generally separate from arachnoid cysts and other cystic lesions of the spine, although these can sometimes appear similar on imaging.
The great majority of Tarlov cysts cause no symptoms and are discovered incidentally during MRI performed for back pain, pelvic pain, or other unrelated reasons. In a smaller number of patients, larger cysts—especially those that erode adjacent bone or compress nerves—can produce symptoms. These may include chronic lower back, buttock, or perineal pain, sciatica-like leg pain, numbness or tingling in the buttock or legs, pelvic or genital discomfort, and, in more significant cases, bowel, bladder, or sexual dysfunction. Symptoms may worsen with prolonged standing, sitting, or activities that increase pressure within the cerebrospinal fluid space, such as coughing, sneezing, or straining. Importantly, many people with Tarlov cysts have separate causes for their back or pelvic pain (such as degenerative disc disease, sacroiliitis, or pelvic floor conditions), so attributing symptoms specifically to the cyst requires careful evaluation.
MRI of the lumbar and sacral spine is the preferred imaging test for identifying and evaluating Tarlov cysts. On MRI, they appear as smoothly marginated, fluid-filled lesions following the course of a nerve root, often associated with subtle scalloping or remodeling of the adjacent sacral bone in larger cysts. CT and CT myelography may be used in select cases. Once a cyst is identified, the imaging findings are interpreted together with the patient’s symptoms and examination, as the presence of a Tarlov cyst alone does not necessarily mean it is the cause of those symptoms.
Important to Know
For most people, a Tarlov 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 the cyst is actually responsible for them or whether another condition is contributing. 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 the cyst, image-guided procedures such as cyst aspiration or fibrin glue injection, or surgical treatment of the cyst, may be considered. These treatments can be helpful in some patients but also carry their own risks, including CSF leak, recurrence, or new neurological symptoms, so they are generally reserved for severe cases and performed in specialized centers.
Because Tarlov 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 clinical picture.
Red flag symptoms include sudden severe back, buttock, or leg 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 or another serious underlying condition rather than a simple Tarlov cyst.