Understanding Tarlov Cysts
A Tarlov cyst is a fluid-filled sac that forms on the nerve root sheath, most commonly found in the sacral region of the spine. While many individuals experience no symptoms, some develop pain, numbness, or weakness when the cysts enlarge and compress surrounding nerves.
These cysts are filled with cerebrospinal fluid (CSF), the clear fluid that surrounds the brain and spinal cord. They most frequently occur in the sacral spine, particularly affecting the S1 to S4 nerve roots. Tarlov cysts are not tumors; they are benign formations that vary in size and number. They are present in 1.5% to 10% of the population, though a smaller fraction become symptomatic.
Visualizing Tarlov Cysts Through Imaging
Because Tarlov cysts are internal structures, their identification relies on medical imaging, particularly Magnetic Resonance Imaging (MRI). MRI provides detailed images of soft tissues, allowing clinicians to visualize the fluid content and relationship of the cyst to surrounding structures. On MRI, Tarlov cysts appear as well-defined, round or oval-shaped lesions. Their size can range from a few millimeters to several centimeters, and individuals may have a single cyst or multiple cysts.
The fluid within Tarlov cysts has signal characteristics similar to cerebrospinal fluid (CSF). They appear bright on T2-weighted MRI sequences and dark on T1-weighted MRI sequences. This distinct signal pattern helps differentiate them from other types of lesions. Imaging also shows their attachment or close proximity to the nerve roots.
Larger Tarlov cysts can exert pressure on adjacent bone structures, leading to visible bone erosion of the sacrum. This erosion is evident on both MRI and computed tomography (CT) scans, which offer better visualization of bone. The presence and extent of bone remodeling provide additional diagnostic clues regarding the cyst’s long-term presence and impact.
Distinguishing Tarlov Cysts
Accurately identifying Tarlov cysts is important because other spinal or sacral lesions can present with similar appearances on imaging. Differentiating Tarlov cysts from conditions like meningeal diverticula, other spinal cysts, or certain tumors requires careful analysis of imaging features. The specific location, the characteristic fluid signal on MRI, and the association with nerve roots are diagnostic indicators.
Radiologists examine these imaging characteristics to arrive at a diagnosis. For instance, the way the cyst communicates with the subarachnoid space and its relationship to the nerve root bundle helps distinguish it from other fluid collections. Even if a Tarlov cyst is asymptomatic, a clear diagnosis is valuable for monitoring and to rule out other conditions that might require different management strategies.