Continuing Education Activity

Tarlov cysts or sacral perineural cysts are an uncommon spinal condition that primarily affects adults. They are often asymptomatic and, as a result, are most commonly picked up as incidental findings on imaging. Traditionally they are thought to not be of clinical consequence, but there is mounting clinical evidence to suggest that the morbidity associated with Tarlov cysts responds well with appropriate treatment. This activity outlines the evaluation and treatment of Tarlov cysts and highlights the role of the interprofessional team in evaluating and treating patients with this condition.

Objectives:

• Review the signs and symptoms that can be associated with Tarlov cysts.
• Outline the differential diagnoses in chronic back pain, including Tarlov cyst.
• Identify radiological features on imaging that suggest or confirm Tarlov cysts.
• Explain the management of symptomatic Tarlov cysts.

Introduction

Tarlov cysts are perineural cysts between the perineurium and endoneurium, arising near the dorsal root ganglion.[1] They can occur anywhere in the spine but most frequently around the sacral nerve roots, with S2 being the most common level.[2] The cysts are usually filled with cerebrospinal fluid but may contain blood if there is a hemorrhagic complication.[3][4] They are mostly asymptomatic but can present as chronic back pain in the sacral or coccyx area and may have radiculopathy or red flag features such as leg weakness, bowel and bladder dysfunction, and sexual dysfunction.[5] The features may also be acute, especially if cyst complications like rupture or hemorrhage occur.

It was originally described on autopsy findings in 1938 by American neurosurgeon Dr. Isadore Tarlov.

Etiology

The exact cause of Tarlov cysts remains unknown. But the cyst is difficult to shrink on its own accord and may grow due to the flow of cerebrospinal fluid into the cyst through a one-way valve system.[6] There is circular scarring of the arachnoid mater around the introitus of the cyst, which forms a valve. This is the target for surgical therapy in some techniques to restore the normal flow of CSF and promote regression.

There is an association with collagen disorders such as Marfan syndrome and Ehlers-Danlos syndrome.[7][8]

Epidemiology

Overall, Tarlov cysts are rare. The most recent published meta-analysis suggests a global prevalence rate of 4.27%; in the United States, it is 3.82% of the population. Tarlov cysts are more common in those of the female sex (female 7.01% vs. male 4.05%). The same study also showed that 15.59% of the cysts are symptomatic.[2]

Pathophysiology

The exact pathophysiological process is not understood well.

Dr. Tarlov's original theory is that due to trauma and hemorrhage, this causes hemosiderin deposition and a blockage of venous drainage in the perineurium and epineurium, leading to cystic degeneration.

Another theory is that genetic risk factors that increase congenital arachnoidal proliferation along with the exiting sacral nerve roots promote the development of the cystic structures.

The cysts themselves are connected to the subarachnoid space, and the leading theory in the growth of cysts is due to a one-way valve mechanism. The pulsatile flow of the CSF allows the cyst to expand but not reduce in size, and it is thought that this explains why only some Tarlov cysts are symptomatic and worsen with time. The growth and pressure that it exerts on adjacent nerve fibers result in neurological symptoms, but it may also erode the surrounding sacral bone and irritate the periosteum, which may also result in pain.[5]

Histopathology

By definition, they would require a nerve root or its fibers in the cyst's wall or cavity.

The cystic lesion under histopathological examination has fibrotic changes, and fibro-collagenous and membraneous connective tissue is the most common finding. Hemorrhage may occur and, as a result, invite an inflammatory process, and macrophages and hemosiderin deposits can be seen. An extensive inflammatory component is rarely observed.[9]

The cysts may be uni-loculated or multi-loculated.

History and Physical

History

Most patients describe a history of chronic or acute-on-chronic back pain, which may be radicular with dermatomal pain, reduced sensation, or weakness.

A study by Hulens et al. has shown that symptomatic Tarlov cysts present more frequently with perineal pain/discomfort, bladder and bowel disturbance, and sexual disturbance (dyspareunia, impotence). They found that patients are more likely to report that their pain worsens with activity (neurogenic claudication), Valsalva maneuvers, and sitting.[10] This may then cause the patients to miss work or social activities.

Other details to cover in the history include trauma, signs, and symptoms of infection, and malignancy.

Examination

A detailed neurological examination should be performed on symptomatic areas.

The dermatomes and myotomes of the lower limbs and perineum, as well reflexes of the lower limbs, and if there are features of urinary retention and anal sphincter tone.

As it is a lower motor neuron lesion, it may result in reduced reflexes and anal tone in addition to sensory loss or motor weakness.[11]

Evaluation

The evaluation is dependent on the healthcare context in which the patient is seen. In general practice or emergency department, the main consideration would be cauda equina syndrome, which may be caused by a large Tarlov cyst.[12] Hence, if cauda equina syndrome is suspected, referral to the local spinal service would be necessary.

As cauda equina syndrome or compression presents a spectrum with varying symptomatology, this is the main diagnosis to exclude, and evaluation is tailored in this manner.[13] The gold standard to achieve this would be a magnetic resonance imaging (MRI) scan of the lumbosacral spine. In cases where MRI is contra-indicated, CT myelography would be an alternative but more invasive.

MRI is currently the preferred imaging modality to evaluate Tarlov cysts. They appear as thin-walled cystic structures that are closely related to nerves. The cyst itself is extra-dural and contains the nerve root within its walls, and is classified as a type 2 spinal meningeal cyst by Nabor et al.[14]

The cyst should appear as a low signal on T1 and a high signal (equivalent to CSF) on T2.[15] Its morphology can vary from simple to complex cysts with loculations and septations. The sacral foramina may be widened.

Treatment / Management

Treatment can be divided into conservative, medical and invasive therapies, which can be further subdivided into percutaneous or open surgical techniques.

Conservative and Medical Treatment

Conservative treatment is the preferred option for asymptomatic, incidentally picked up Tarlov cysts.

Medical therapy is generally analgesics, such as paracetamol, non-steroidal anti-inflammatory agents (NSAIDs), opiates, anti-depressants such as amitriptyline, and anticonvulsants such as pregabalin and gabapentin.[16]

Caudal epidural steroid injections have been described as a treatment with good effect for patients with bladder pain syndrome type symptoms and incidental Tarlov cysts.[17] However, its use is not widespread.

Percutaneous Therapies

The cyst can be aspirated, or through a newer two-needle technique, the cyst can be aspirated and injected with fibrin glue to reduce the dead space and reaccumulation of CSF.

The aspiration-injection technique will have a needle deep in the cyst and a superficial second needle to allow fluid to be aspirated from the deep needle and allow air to enter through the superficial needle.

The air-fluid level that develops can be monitored using CT fluoroscopy, or alternative, an iodinated contrast agent that would allow visualization through an image intensifier. However, the agent would fill up and reduce the effectiveness of the injected fibrin glue.

Once communication with the thecal sac is established by rapid refilling of the cyst, a fibrin glue such as Tisseel is used to plug the cyst.[18]

Open Surgical Techniques

Microsurgical

This option includes cyst excision or fenestration with subsequent imbrication and dural repair. The repair is often then covered with a patch and/or Tisseal to reduce the incidence of CSF leak.[19] The nerve root is often left intact, but excision of the nerve root has been described as a possibility; however, it is not popular in literature.[20]There are newer techniques described, such as occlusion of introitus and communicating channels with muscle graft, and puckering of cyst after fenestration to reduce reaccumulation of CSF.[21][22]Radical Techniques

Decompressive laminectomy is less often practiced, but single-level laminectomies can be offered. A keystone article identified that 7 out of 10 patients that received treatment had complete or substantial resolution with follow-up on average of over two years. The authors noted that cysts above 1.5cm correlated with better outcomes, but this has been shown to not be statistically significant in meta-analysis in recent publications.[23][24] However, cyst size was not commonly reported.

Shunting - This can include lumbo-peritoneal or cyst-subarachnoid shunts.

Complications of Invasive Treatment

Surgery is associated with higher complication rates compared to percutaneous procedures.

Specific complications include 

• Surgical site infection
• CSF leak and pseudomeningocele - usually due to inadequate closure of the dura (iatrogenic durotomy)
• Worsening or new bladder dysfunction
• Failure of treatment - in the form of recurrence of symptoms or cyst[24]

Differential Diagnosis

If the presentation is chronic back pain, considerations range from mechanical back pain to cauda equina compression and spine infection such as discitis or malignancy.[25]

Radiologically, the diagnosis itself is usually straightforward, and no other differentials are entertained. However, in borderline cases on imaging, differentials would include the following:

• Dural ectasia - similar in presentation and associated with Marfan syndrome[26]
• Malignancy - Metastatic deposit or nerve sheath tumors such as a schwannoma[27]
• Spinal synovial cysts
• Meningocele (do not contain neural tissue by definition)
• Cysticercosis[28]

Prognosis

For treated Tarlov cysts, symptom relief is generally good and does not appear to significantly differ initially between surgical treatment over percutaneous treatment. However, the recurrence rates are lower in surgically treated cysts compared to percutaneously treated cysts (8% over 20%). This may be limited by the length of follow-up as surgically managed patients are, on average, followed up for longer compared to percutaneously treated ones (38 months vs. 15 months).[29]

In terms of symptom relief, it is reported that 81% of patients treated surgically remain symptom-free at one year, similar to the cyst being completely or substantially reduced in size (79%).[24] 

Complications

Complications are generally cyst wall rupture and hemorrhage into the cyst, both of which are rare. This may intensify pre-existing or produce new symptoms such as radiculopathy or even mimicking cauda equina syndrome.[30][31] Bleeding from an intracranial subarachnoid hemorrhage has also been reported to track into the Tarlov cyst and produce similar symptoms.[32]

In perhaps exceedingly rare circumstances, a sacral fracture following trauma may leak intra-medullary contents through a Tarlov cyst and produce acute cerebral fat embolism.[33]

The appearance of a hemorrhage within a Tarlov cyst may re-present features of intradural carcinomatosis, which may lead to unnecessary investigations and management for the patient.[34]

Deterrence and Patient Education

The reasons for symptoms require careful exploration to manage the patient's expectations and clinical outcomes. It must be stressed that Tarlov cysts may not be the sole cause of symptoms, and evaluation should attempt to look for other causes of symptoms.[35] Once all possible causes are found, then careful consultation, including the risks, benefits, and recurrence of cyst or symptoms, should be explained to the patient. An interprofessional team approach should be used to improve patient outcomes.

Enhancing Healthcare Team Outcomes

Tarlov cysts are often overlooked due to several factors. This can lie with the physician or radiologist responsible for interpreting the imaging, as Tarlov cysts are considered clinically irrelevant, and other degenerative spine conditions are usually blamed as the reason for the patient's symptoms. It is also difficult to use an objective measure to ascertain that Tarlov cysts are the reason for symptoms. And when imaging or electromyography is used to try to confirm, they are often limited to L1 - S1 nerve roots.[36]

Treatment is therefore also controversial, but methods to treat exist. Careful selection of levels and reasons for symptoms is crucial to maximizing treatment effectiveness. Recurrence of cysts and symptoms may occur despite initial effective treatment and must be highlighted to manage patient expectations. This, therefore, would require an interprofessional team approach - usually comprising of a pain specialist, spinal surgeon, specialist nurses, family medicine doctor (including PAs and NPs), and the patient.