Tarlov Cyst or Perineural Cysts : Causes, Symptoms, Diagnosis

Perineural cyst is a meningeal cystic sac which develops from meningeal covering of spinal nerve close to spinal cord. Perineural cyst is also known as Tarlov cyst. Isadore Tarlov described the symptoms of pinched nerve caused by perineural cyst in 1938. The cyst is more common and often seen in sacral segment of spinal cord. The cyst in rare cases is also observed in neck, thoracic or lumbar segment of spinal cord. Tarlov cyst or perineural cyst are located near dorsal root ganglion and cyst is filled with cerebrospinal fluid. More than single Tarlov Cyst is rare but seldom seen in few cases. Asymptomatic Tarlov Cyst are observed in CT Scan and MRI as an incidental finding.

Tarlov cyst or perineural cysts are categorized into the list of type II innervated meningeal cysts. The Tarlov Cyst or perineural cyst are filled with the cerebrospinal fluid (CSF). Tarlov Cyst is most often seen in sacral nerves and lies within lower lumbar or sacral spinal canal. Cyst is located at the base of the spinal nerve close to spinal cord. Thus the disease or symptomatic condition caused by Tarlov Cyst is also known as Myelopathy or disease of spinal cord.

The true causes of Tarlov Cyst or perineural cyst formation is not yet well established in published research data. The published data of lab studies and investigational data often elaborate the cause of Tarlov cyst as congenital, secondary to inflammation of spinal meningeal covering, caused by traumatic injury of spinal covering, hypertrophy or proliferation of spinal meninges and hemosiderin deposits over the meninges following trauma that follows proliferation of meninges. Inflammation of spinal meninges is diagnosed as arachnoiditis. The persistent local inflammation of spinal covering like arachnoiditis causes weakness in covering of spinal meninges that may eventually form a Tarlov cyst.¹ As the sacs are filled with CSF, many researchers feel that it has something to do with the abnormal communication between the subarachnoid space containing CSF or cerebrospinal fluid and perineural region. Any increase in the CSF or cerebrospinal fluid pressure can push CSF into meningeal covering of spinal nerve and force to form a cyst or sac around weak meninges covering. Some studies have reported that disorders in connective tissues make individuals more prone to Tarlov cyst or perineural cyst. Tarlov Cyst was identified as a cause of back pain and cauda equina syndrome in patient suffering with rare connective tissue disorder known as Ehlers-Danlos Syndromes.²

1. Neck, Thorax and Upper Lumbar segment

   Generally, the disease is asymptomatic until the size of the tarlov cyst is large enough to cause irritation or pinch of spinal nerve. Single large Tarlov Cysts more than 1 cm in diameter can cause irritation or pinch of spinal nerve in neck, chest and upper lumbar segment. Similarly, multiple Tarlov Cyst causes irritation or pinch of multiple spinal nerves. The irritation or pinch of sensory nerve causes symptoms like pain, paresthesia, tingling and numbness. The pain symptom is also known as radicular pain when it spreads along the course of the nerve.³

   Similarly, irritation or pinch of motor division of spinal nerve causes symptoms like spasticity, weakness and segmental muscle paralysis. In few cases large cyst may cause simultaneous irritation or pinch of sensory and motor nerve fibers resulting in symptoms like pain, numbness and weakness, which is also known as radiculopathy.

2. Symptoms and Signs Caused by Tarlov Cyst in Lower Lumbar and Sacral Segment

   The spinal cord splits below the second lumbar vertebra into multiple bundle of 3 lumbar and 5 sacral nerves known as cauda equina. Cauda equina means bundle of nerves looks like tail of the horse. The following nerve fibers form cauda equina- Lumbar third, fourth, fifth nerve and Sacral one, two, three, fourth and fifth nerves. The lumbar 3 nerves (L1 to and sacral first nerve S1 contains sensory and motor nerve fibers, while sacral nerves 2nd to 5th (S2, S3, S4 and S5) contains sensory, motor and parasympathetic autonomic nerves fibers. The Tarlov Cyst of lower lumbar (L3 to 5) and sacral nerve (S1 to S5) lies within lower lumbar spinal canal. The cyst constantly puts pressure on the adjacent nerves within cauda equina causing sensory, motor and autonomic dysfunction and abnormal symptoms. These abnormal sensory, motor or autonomic symptoms are known as cauda equina syndrome.⁴ Irritation or pinch of sensory nerve causes pain, tingling and numbness spread over back, perineum, buttocks, inguinal area and lower leg. The radicular pain is also known as sciatica when pain radiates along the back of the lower leg. The irritation or pinch of motor nerve or nerve to muscles causes symptoms like piriformis muscle dysfunction, pelvic floor muscle dysfunction, muscle weakness in gluteal area, groin, and lower leg. The irritation or pinch of autonomic nerve causes neurogenic bladder, dysuria, bowel dysfunction, retrograde ejaculation, impotence and urinary incontinence. The combination of abnormal sensory, motor and autonomic symptoms is known as cauda equina syndrome.⁵ If the treatment for initial symptoms like weakness in leg are not initiated soon then individual may suffer with paralysis of leg muscles. Most of the cases of Tarlov Cyst or perineural cyst remain undiagnosed, as there are no early symptoms. Professionals and doctors can detect Tarlov Cyst or perineural cyst only by using the imaging techniques or myelogram.

3. Can Tarlov Cyst or Perineural Cyst Cause Back Pain?

   Tarlov cyst or perineural cyst may be associated with the back pain. As the cyst grows larger, the cyst generates pressure over facet and sacroiliac joint resulting in back pain.⁶ The back pain is also caused by irritation of sensory and motor nerves, which are supplying sensory and motor fibers to lower back. Irritation of these sensory and motor nerve fibers within spinal nerve by Tarlov Cyst causes pain spread over paravertebral or gluteal muscles as well as soft tissue of the lower back like skin and subcutaneous tissue. The degeneration of these sensory and motor nerve fibers are caused by continuous pressure and irritation by Tarlov Cyst. The irritation of motor fibers also causes paravertebral and gluteal muscles spasm or spasticity resulting in moderate to severe back pain.

There are few tests available for diagnosing Tarlov Cyst or perineural cyst.

Radiological Studies – Plain X-Ray is not able to pinpoint the Tarlov Cyst in spinal canal. CT Scan and MRI often shows incidental Tarlov Cyst when test is performed to diagnose the cause of back pain or sciatica. Most radiological investigational studies for back pain, radicular pain, numbness and weakness in legs are performed to rule out disc herniation or bulge disc. These studies sometime show the cystic swelling of Tarlov Cyst around the nerve root, which is further evaluated by EMG and Myelogram studies.

Electromyography (EMG) Studies⁷ – The continuous irritation and pressure from large cyst causes degeneration and damage of sensory and motor nerves. EMG studies are performed to evaluate the abnormalities indicating damage nerve.

Myelography Studies – Myelography study involves injection of dye in CSF and followed by CT Scan. Tarlov Cyst or Perineural cyst in most cases do not show filling of dye in the cyst immediately following the procedure. One of the study suggests injection of Pantopaque and performing CT scan study after 3 to 4 days of injection of dye Pantopaque or in some cases after 1 to 2 weeks may show dye filing in the Tarlov Cyst.⁸

Also Read:

• Treatment of Tarlov Cyst or Perineural Cyst & its Recovery Period
• Tarlov Cyst or Perineural Cysts: Prevention, Social Security, Prognosis, Coping

References: