Tarlov cysts are uncommon fluid-filled sacs that develop along the nerve roots of the spine, primarily in the sacral region at the base of the back. Also known as perineurial cysts, they form within the protective sheath surrounding a nerve root and are typically filled with cerebrospinal fluid (CSF). While many people have these cysts without symptoms, enlargement can cause pressure on adjacent nerve structures, leading to neurological issues.
The Anatomy and Formation of Tarlov Cysts
Tarlov cysts originate from the perineurial space, which is the area between the endoneurium and perineurium layers of the nerve root sheath. They are most frequently located in the sacrum, the triangular bone at the base of the spine, typically involving the S1 through S4 nerve segments. A unique feature distinguishing these from other spinal lesions is that the walls of the cysts often contain actual nerve fibers or tissue. This anatomical detail is why Tarlov cysts are sometimes referred to as nerve root cysts.
The exact process that leads to the formation of a Tarlov cyst remains unclear, but several theories exist. One prominent hypothesis suggests that a one-way valve mechanism allows cerebrospinal fluid to enter the nerve sheath but prevents it from easily flowing back out. This continuous, pulsatile flow of CSF into the cyst can cause it to gradually expand over time. Other factors proposed include congenital defects, inflammation, or trauma to the spine that may cause a blockage of venous drainage within the nerve sheath.
The accumulation of CSF within the sac is influenced by fluctuations in spinal fluid pressure. Conditions like heavy lifting, falls, or childbirth have been anecdotally associated with the onset of symptoms, suggesting that abrupt pressure changes may increase the size of a previously asymptomatic cyst. Unlike meningoceles, which are outpouchings of the dura mater that do not contain nerve fibers, a Tarlov cyst is defined by its involvement with the nerve root itself.
When Tarlov Cysts Cause Symptoms
The majority of Tarlov cysts are discovered incidentally during imaging for unrelated conditions, meaning they are asymptomatic. Symptoms only arise when the cyst enlarges sufficiently to compress the adjacent nerve root or erode the surrounding bone. This mechanical compression of the sacral nerves causes the onset of clinical issues, often referred to as Tarlov cyst disease.
The most common complaints involve pain localized in the sacral area, buttocks, and perineum. Because the cysts primarily affect the sacral nerve roots, they often cause radicular pain that radiates down the back of the leg, similar to sciatica. Patients may also experience paresthesia, a sensation of tingling or numbness, in the legs and feet. The pain often worsens with activities like sitting, standing, or walking, and may only find relief when lying down.
When the cysts grow large enough, they can cause significant neurological deficits affecting the lower body and pelvic region. Compression of the S2, S3, and S4 nerves can lead to neurogenic bladder or bowel dysfunction, resulting in difficulty with urination, constipation, or incontinence. In severe cases, patients may also report muscle weakness, loss of reflexes, or sexual dysfunction, indicating profound nerve damage.
Identification and Diagnostic Procedures
Diagnosis typically begins with a physical and neurological examination, combined with a review of the patient’s symptoms and medical history. Since the symptoms of a Tarlov cyst can mimic those of a herniated disc or other spinal issues, definitive diagnosis relies on medical imaging. The standard tool for visualizing these fluid-filled sacs is Magnetic Resonance Imaging (MRI).
An MRI clearly shows the size, location, and fluid content of the cysts, which appear as characteristic dilations along the sacral nerve roots. This imaging technique confirms the presence of a Tarlov cyst and rules out other potential causes of nerve compression. In complex cases, a Computed Tomography (CT) Myelography may be performed. This procedure involves injecting a contrast dye into the spinal canal to determine if the cyst is communicating with the subarachnoid space and to help map the fluid dynamics.
Management and Treatment Approaches
Management of Tarlov cysts follows a tiered approach, depending on the presence and severity of symptoms. Asymptomatic cysts are managed with observation and periodic follow-up imaging to monitor for changes in size or appearance. For patients experiencing mild to moderate pain, conservative management is the first line of defense. This can include nonsteroidal anti-inflammatory drugs (NSAIDs), physical therapy, and nerve block injections to manage localized pain.
If conservative methods fail to provide adequate relief, minimally invasive procedures may be considered. One option is cyst aspiration, which involves draining the cerebrospinal fluid from the cyst, often guided by CT imaging. This is sometimes followed by an injection of a fibrin glue patch to close the connection to the subarachnoid space and prevent the cyst from refilling. However, aspiration carries a risk of recurrence because the one-way valve mechanism may still be present.
Surgical intervention is generally reserved for patients with severe, persistent pain or progressive neurological deficits, such as significant muscle weakness or bladder and bowel impairment. The goal of surgery is to decompress the affected nerve root by reducing the cyst’s size and preventing it from re-filling. Surgical techniques include fenestration (opening and draining the cyst) and imbrication (folding and suturing the cyst wall to seal it off from CSF flow). Due to the complexity and close proximity of the cyst walls to nerve tissue, this specialized surgery is often performed by neurosurgeons experienced in spinal pathology.