Tarlov cysts are rare, fluid-filled sacs that develop along the nerve roots of the spine, primarily in the sacral region. They are often referred to as perineural cysts because they form directly on the protective sheath surrounding a spinal nerve root. While present in a small percentage of the population, most individuals with Tarlov cysts do not experience related health issues, leading to their discovery being incidental during imaging for other conditions.
Anatomical Nature and Location
Tarlov cysts are classified as perineural cysts, arising from the nerve root sheaths that extend from the spinal cord. The fluid inside is cerebrospinal fluid (CSF), which surrounds and cushions the brain and spinal cord. CSF accumulates within the dilated nerve root sheath, causing the sac-like structure to form.
These cysts are overwhelmingly concentrated in the sacrum, the triangular bone at the base of the spine, typically affecting the S1 to S4 nerve root area. The sacrum is a fused set of vertebrae situated close to the pelvic region, which explains the specific symptoms that can occur when a cyst grows large. The exact formation mechanism is largely unknown, but one theory suggests that CSF enters the nerve root sheath and becomes trapped, leading to expansion.
Other theories suggest that increased CSF pressure, perhaps due to trauma or inflammation, may cause an existing cyst to enlarge and become symptomatic. The distinguishing feature of a Tarlov cyst, compared to other spinal lesions, is the presence of nerve root fibers within the cyst wall or its cavity. This intimate connection to nerve tissue makes them a potential source of pain and neurological dysfunction when they expand.
Symptom Manifestation and Severity
Up to 80% of Tarlov cysts remain entirely asymptomatic and do not require treatment. When symptoms manifest, they arise because the expanding cyst compresses or irritates the delicate nerve roots against the surrounding bone. Symptom severity is highly variable and often depends on the cyst’s size and the specific nerve root affected.
The most common symptoms relate to nerve root compression, known as radiculopathy, presenting as localized pain in the lower back, buttocks, or perineum. This pain can be sharp, burning, or shock-like and frequently radiates down the back of the leg, mimicking sciatica. Sitting or standing for extended periods can intensify the discomfort by increasing pressure on the sacral nerve roots.
Compression of the sacral nerves (S2, S3, S4) can lead to specific neurological issues, including numbness or a pins-and-needles sensation (paresthesia) in the legs or feet. In severe cases, the pressure can compromise nerve function responsible for bowel and bladder control. This may result in difficulty with urination, increased frequency, or incontinence, as well as constipation or other bowel irregularities.
Diagnosis and Management Approaches
Diagnosis begins with a thorough neurological evaluation and medical history to assess symptoms and rule out other common causes of nerve compression, such as a herniated disc. Definitive diagnosis is achieved through medical imaging, with Magnetic Resonance Imaging (MRI) considered the preferred technique. A dedicated sacral MRI provides detailed images of the spine’s base, allowing clinicians to visualize the size and exact location of the fluid-filled sac and its relationship to the nerve roots.
A Computed Tomography (CT) Myelography may be used, which involves injecting a contrast dye into the spinal fluid to better outline the cyst’s connection to the main spinal canal. Once a symptomatic cyst is confirmed, management is tailored to the severity of the patient’s symptoms. For small, asymptomatic, or mildly symptomatic cysts, the recommended approach is conservative management.
Conservative treatments focus on relieving discomfort and managing pain through medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or nerve pain medications like gabapentin. Physical therapy may be recommended to improve mobility and reduce secondary pain. If conservative methods fail or if the patient experiences severe neurological deficits, surgical intervention may be considered.
Surgical options are reserved for highly symptomatic cysts and typically involve procedures like cyst fenestration (where the cyst is opened and drained) or shunting to divert the fluid. Another technique is fluid aspiration followed by the injection of fibrin glue, a sealant that aims to block the flow of CSF back into the cyst, although recurrence is possible. Due to the proximity of the cysts to delicate nerve tissue, these procedures carry risks, including potential nerve damage or fluid leaks, and are often performed by experienced neurosurgeons.