Are Perineural Cysts Dangerous? Symptoms & Outlook

Most perineural cysts, also called Tarlov cysts, are harmless fluid-filled sacs along spinal nerve roots that never cause a single symptom. They are typically discovered by accident on an MRI ordered for something else. In a minority of people, though, these cysts enlarge enough to press on nerves, producing pain, bladder problems, and other neurological symptoms that can significantly affect daily life. Rare complications, including bone erosion and nerve-bundle compression, push a small fraction of cases into genuinely dangerous territory.

What Perineural Cysts Are and Why Most Stay Harmless

Perineural cysts are sacs filled with cerebrospinal fluid that form along the sheaths of spinal nerve roots. They appear most often in the sacrum, the triangular bone at the base of the spine, though they can occasionally develop at thoracic or cervical levels.¹ Most of them sit quietly at a small size for years, even decades, without growing or compressing anything. People can live their entire lives with one or more of these cysts and never know it.

What separates a harmless cyst from a troublesome one comes down to fluid dynamics. The cyst wall has tiny connections to the space surrounding the spinal cord, allowing cerebrospinal fluid to trickle in and out. In some cysts, a one-way valve effect develops: fluid flows in more easily than it flows out. Over time, pressure builds and the cyst slowly expands, eventually pressing against neighboring nerve fibers. Cysts that allow fluid to circulate freely in both directions tend not to enlarge and rarely cause problems.²

How Common They Are

Estimates vary depending on who gets scanned and why, but one study of patients undergoing spinal MRI for back pain found Tarlov cysts in about 1 in 15 people.³ That number is likely higher than you would see in the general population, because people already having back pain are more likely to get an MRI. Still, it suggests these cysts are far from rare. The vast majority of them, even in people who do have back pain, are not actually responsible for the symptoms that prompted the scan.

Surgical series consistently show that roughly nine out of ten patients who end up needing treatment for symptomatic Tarlov cysts are women.⁴ Whether women actually develop symptomatic cysts more often or are simply more likely to seek care is not entirely settled, but the skew is dramatic enough that most researchers believe there is a real biological predisposition.

Symptoms When a Cyst Does Cause Problems

When a perineural cyst grows large enough to compress a nerve root, the most common complaint is pain. It often shows up as sciatica-like pain radiating into the buttock or leg, sometimes mimicking a herniated disc so closely that the cyst gets overlooked at first.⁵ People describe it as burning, aching, or shooting pain that worsens with sitting, standing for long periods, or coughing and straining.

Because sacral nerve roots also control pelvic organs, symptomatic cysts frequently produce problems that patients and even some doctors do not immediately connect to a spinal cyst. In one study of patients with confirmed symptomatic sacral Tarlov cysts, urinary symptoms appeared in roughly nine out of ten patients, sexual dysfunction in about eight out of ten, and bowel symptoms in about seven out of ten.⁶ These included urinary urgency, difficulty emptying the bladder fully, constipation, and pain during intercourse. Larger cysts are more strongly associated with urinary symptoms: one study found that cysts in women reporting urinary problems were on average about 4 mm larger than those without.⁷

Because pelvic symptoms can look like a urological, gynecological, or gastrointestinal problem, patients often bounce between specialists for months or years before anyone thinks to look at the spine. Some undergo unnecessary abdominal surgeries before the cyst is identified.⁸

Rare but Serious Complications

In uncommon cases, a perineural cyst crosses from “painful nuisance” into genuinely dangerous. The two main serious complications are bone erosion and cauda equina syndrome.

An expanding cyst sitting inside the sacral canal exerts slow, steady pressure on the surrounding bone. Over time this can thin the sacrum enough to cause an insufficiency fracture, where the bone breaks under normal loads that a healthy sacrum would handle without trouble.⁹ These fractures sometimes require not just draining the cyst but stabilizing the pelvis with hardware. A systematic review confirmed that bone erosion from expanding cysts can produce inflammation and pain even before an outright fracture occurs.¹⁰

Cauda equina syndrome is the more urgent scenario. The cauda equina is the bundle of nerve roots at the bottom of the spinal cord that controls the legs, bladder, bowel, and sexual function. If a Tarlov cyst compresses this bundle suddenly, it can cause acute back pain with radiating leg symptoms, loss of bladder or bowel control, and numbness in the saddle area. One reported case involved hemorrhage inside a Tarlov cyst that rapidly compressed the cauda equina, producing bilateral leg pain and urinary dysfunction.¹¹ Multiple Tarlov cysts in the lumbosacral region have also been documented as a cause of cauda equina syndrome even without hemorrhage.¹² If you develop sudden bladder or bowel incontinence alongside worsening back or leg pain, that warrants emergency evaluation regardless of the suspected cause.

Why Diagnosis Can Be Tricky

A Tarlov cyst shows up clearly on MRI, so finding one is not the hard part. The hard part is figuring out whether the cyst you found is actually responsible for a patient’s symptoms. Many people with back pain, sciatica, or pelvic symptoms also have disc herniations, spinal stenosis, or other common conditions that could explain the same complaints. A cyst sitting quietly alongside a herniated disc can be a red herring, or the disc can be the red herring.

One case illustrates this problem starkly. A patient with S1 radiculopathy had both a sacral perineural cyst and a disc herniation at L5-S1. Surgeons addressed the disc first with a discectomy, but the patient’s leg pain and numbness did not improve, because the cyst was the actual culprit.¹³ Advanced imaging can sometimes help sort this out. Post-myelographic CT scanning, where contrast dye is injected into the spinal fluid, can show whether fluid is actively filling a cyst in a one-way pattern, which strengthens the case that the cyst is the source of trouble.¹⁴

The diagnostic confusion contributes to a pattern documented across large referral populations: patients with symptomatic Tarlov cysts frequently experience long delays, repeated visits to the wrong specialists, and even unnecessary surgical procedures before receiving an accurate diagnosis.⁸

Conservative Approaches for Symptomatic Cysts

Not every symptomatic cyst needs surgery. For patients whose symptoms are moderate and not rapidly worsening, conservative management is a reasonable first step. This typically includes pain medication, short courses of oral corticosteroids to reduce inflammation around the nerve root, and structured physical rehabilitation. Two case reports documented patients with symptomatic sacral cysts who improved substantially with this combination: radicular pain resolved or markedly decreased, and follow-up imaging showed no cyst progression in one patient and partial shrinkage in the other.¹⁵

Physiotherapy-focused approaches have also shown benefits. In one reported case involving Tarlov cysts with cervical radiculopathy, a two-week physiotherapy program produced measurable improvements in pain intensity, range of motion, and functional scores.¹⁶ Nerve blocks offer another option for managing pain without operating. In a case of thoracic perineural cysts causing intercostal neuralgia, a nerve block provided relief, though the pain recurred after about nine months and required a repeat procedure.¹⁴

Conservative treatment has clear limits. It manages symptoms rather than eliminating the cyst. For people whose cysts continue to enlarge or whose neurological function is declining, waiting too long may allow irreversible nerve damage.

Fibrin Glue Injection

A middle ground between conservative management and open surgery is CT-guided percutaneous injection of fibrin sealant. Under imaging guidance, a needle drains the cyst’s fluid and then injects a biological glue that seals the cyst walls together, preventing refilling. The largest published series followed 213 patients treated this way. One year after the procedure, about 82% reported satisfactory or better outcomes, with more than half calling their results excellent. At three to six years of follow-up, roughly 74% remained satisfied, and no clinically significant complications were reported.¹⁷

A smaller series using the same basic technique on arachnoid cysts reported positive outcomes in about 87% of patients with no serious complications.¹⁸ Individual case reports have documented complete cyst resolution and symptom relief following the procedure.¹⁹ The appeal of this approach is that it avoids the recovery time and risks of open surgery while offering more durable relief than pain management alone. The trade-off is that some cysts refill over time, and not every cyst configuration is suitable for percutaneous access.

Surgical Options and What the Numbers Say

For patients with large, expanding cysts causing significant neurological deficits, surgery becomes the most direct option. The two main open techniques are cyst fenestration, where the surgeon opens and drains the cyst, and nerve root imbrication, where the cyst is removed and the nerve root sheath is reconstructed and tightened to prevent recurrence. In one institutional series of 39 patients, about 80% to 82% reported improved outcomes regardless of which technique was used. However, the complication rate was significant: 42% in the fenestration group and 22% in the imbrication group, with an overall rate of 28%.²⁰

A larger systematic review and consecutive series of 97 patients found symptom improvement in 76% with a complication rate of about 18%.²¹ A prospective study of 144 surgical patients showed continued improvement in quality-of-life scores out to 12 months, with about 82% reporting improvement overall. Patient age and how long symptoms had been present before surgery did not seem to predict who would do better or worse.⁴

Surgical clipping of the cyst’s connection to the subarachnoid space is another approach that has shown effectiveness for resolving bladder dysfunction when urinary symptoms are intermittent and incomplete.²² For the subset of patients whose cysts recur after initial surgery, more advanced microsurgical techniques have been developed. One series reported complete disappearance of recurrent cysts on follow-up imaging with no new neurological deficits after a reinforced repair procedure.²³

The honest picture is that surgery helps most people who need it, but complication rates in the range of 18% to 28% are not trivial. Common complications include cerebrospinal fluid leaks, wound healing problems, and temporary neurological changes. That risk-benefit calculation is why most specialists reserve surgery for patients with clearly documented, progressive neurological symptoms rather than pain alone.

Connective Tissue Disorders and Perineural Cysts

There is a recognized association between perineural cysts and connective tissue disorders, particularly Ehlers-Danlos syndrome. In people with this genetic condition, the structural proteins that give tissues their strength and elasticity are abnormal. This can make nerve root sheaths more prone to stretching and ballooning under the normal pressure of cerebrospinal fluid. One documented case involved an 11-year-old boy with Ehlers-Danlos syndrome who developed urinary and bowel incontinence from a Tarlov cyst, a presentation unusual both for his age and for the severity of pelvic symptoms.²⁴

If you have a connective tissue disorder and develop new back pain, pelvic symptoms, or neurological changes in the legs, it is worth mentioning the possibility of a perineural cyst to your doctor rather than assuming the problem is muscular or joint-related. These cysts can appear earlier in life and behave more aggressively in people whose tissues are inherently more fragile.

Pregnancy as a Risk Period

Pregnancy appears to be a time when existing Tarlov cysts can worsen. The combination of increased abdominal pressure, hormonal changes that loosen connective tissue, and shifts in cerebrospinal fluid dynamics may promote cyst expansion. One case report described a 24-year-old woman who developed foot numbness in her third trimester. Shortly after delivery, she progressed to ascending paralysis with bladder and bowel incontinence.²⁵ While this is an extreme outcome and not what happens to most pregnant women with Tarlov cysts, it underscores that new or worsening neurological symptoms during pregnancy should not be dismissed as normal pregnancy discomfort.

The Social and Psychological Toll

One aspect of symptomatic Tarlov cysts that clinical outcome numbers do not capture well is the toll of living with a condition that many doctors have never heard of or consider unimportant. A review of more than 1,000 patient referrals found that diagnostic delays, dismissal by physicians, and the chronic nature of symptoms drove significant social and psychological consequences. Patients were substantially more likely to reduce social activities, lose employment, and experience an overall decline in quality of life compared to what would be expected from the severity of the underlying lesion alone.⁸

Part of the problem is that the medical community itself has historically treated these cysts as incidental findings that do not need attention. When a radiologist’s report describes a Tarlov cyst as “incidental” and a primary care doctor echoes that framing, a patient whose pelvic pain, bladder dysfunction, or leg weakness is actually being caused by the cyst can spend years feeling unheard. The situation is gradually improving as more neurosurgical centers develop specific expertise in evaluating and treating symptomatic Tarlov cysts, but finding a specialist who takes these lesions seriously remains a real challenge in many parts of the world.