Tarlov cysts, also known as perineural cysts, are cerebrospinal fluid (CSF)-filled lesions that most commonly develop in the sacral region of the spinal canal (S1–S5), and less frequently in the cervical, thoracic, or lumbar spine. These cysts form as dilations of the nerve root sheath near the dorsal root ganglion, specifically within the perineural space between the endoneurium and perineurium. A defining feature is that the cyst walls contain nerve fibers, which often line the inner cavity of the cyst itself. This involvement of neural elements distinguishes Tarlov cysts from other extradural meningeal cysts, such as meningeal diverticula, which do not contain nerve fibers.
The etiology of these cysts is not well understood; some current theories explaining this phenomenon include increased spinal fluid pressure, filling of congenital cysts with one-way valves, and/or inflammation in response to trauma and disease. They are named after an American neurosurgeon Isadore Tarlov, who described them in 1938.
These cysts are often detected during MRI or CT scans. They are also observed using magnetic resonance neurography with communicating subarachnoid cysts of the spinal meninges. Cysts with diameters of 1cm or larger are more likely to be symptomatic; although cysts of any size may be symptomatic dependent on location and etiology. Some 40% of patients with symptomatic Tarlov cysts can associate a history of trauma or childbirth. Current treatment options include CSF aspiration, Aspiration and Fibrin Glue Injection (AFGI), laminectomy with wrapping of the cyst, among other surgical treatment approaches. Interventional treatment of Tarlov cysts is the only means by which symptoms might permanently be resolved due to the fact that the cysts often refill after aspiration. Tarlov cysts often enlarge over time, especially if the sac has a check valve type opening. They are differentiated from other meningeal and arachnoid cysts because they are innervated and diagnosis can in cases be demonstrated with subarachnoid communication.
Tarlov perineural cysts have occasionally been observed in patients with connective tissue disorders such as Marfan syndrome, Ehlers–Danlos syndrome, and Loeys–Dietz syndrome.
History
Perineural cysts were first described by Dr. Isadore Tarlov in 1938. While conducting anatomical dissections of 30 human cadavers to study the filum terminale and lower spinal nerve roots, Tarlov identified cystic lesions on the S2 to S5 sacral nerve roots in five specimens, ranging in size from a pinhead to approximately 2 cm. He also reported degenerative changes in the nerve fibers, ganglion cells, and disintegration of myelin sheaths. These observations were published in a paper titled "Perineurial Cysts of the Spinal Nerve Roots (1938)", in which he suggested the possible clinical relevance of the cysts, stating:
"One wonders whether they may not be responsible for the discomfort in certain cases of sciatica or nerve root pains, in which any other pathologic basis has been excluded. This awaits further studies with clinical and pathologic correlations."
In 1948, Tarlov reported the first clinical case linking sacral perineural cysts to sciatic pain, establishing their potential as a treatable cause of radiculopathy. He described a 42-year-old woman who developed persistent right-sided sciatica following a fall. Although a herniated intervertebral disc was initially diagnosed, surgical exploration revealed a perineural cyst arising from the right S2 sacral nerve root, located under the posterior arch of the sacrum. The lesion was excised along with part of the dorsal root and ganglion. Postoperatively, the patient experienced significant improvement in motor function, pain, and sensation, without complications. Tarlov concluded that such cysts, though often overlooked during standard imaging or surgery, could produce clinically significant symptoms and should be considered in cases of unexplained sciatic pain. He published these findings in the paper "Cysts (Perineurial) of the Sacral Roots: Another Cause (Removable) of Sciatic Pain" (1948).
In 1952, Tarlov published his third paper on perineurial cysts, titled "Cysts of the Sacral Nerve Roots: Clinical Significance and Pathogenesis". In this work, he acknowledged the limitations of his earlier cadaver studies due to incomplete medical records, noting that the symptomatic relevance of the cysts was initially unclear. The paper presented detailed accounts of two surgical cases from 1950 and 1951 in which sacral nerve root cysts were associated with neurological symptoms. The first patient, a 28-year-old man with progressive numbness, urinary incontinence, and sexual dysfunction, was found to have bilateral S2 cysts; surgical removal of the right cyst and drainage of the left halted symptom progression and improved bladder function. The second case involved a 70-year-old woman with paresthesia in the right leg and vaginal area, foot weakness, and sacral tenderness, in whom four cysts were discovered on the S2 and S3 nerve roots. Partial excision led to improvement in foot strength and partial symptom relief. Tarlov also discussed two post-mortem cases in which subarachnoid hemorrhages and sacral cysts coexisted, prompting the hypothesis that the cysts might occasionally form secondary to hemorrhagic damage to nerve roots. He concluded that perineurial cysts should be considered in patients with gradually worsening sacral nerve symptoms when imaging or surgery fails to reveal a herniated disc.
In 1953, Dr. Isadore Tarlov published a monograph titled Sacral Nerve-Root Cysts: Another Cause of the Sciatic or Cauda Equina Syndrome, which compiled his anatomical, histological, and clinical research on perineurial cysts. The book combined scientific analysis with case studies to illustrate the symptoms, surgical techniques, and outcomes associated with sacral cysts. In Chapter 8, titled "Clinical Significance", Tarlov presented ten patient case reports documented between 1948 and 1952, four of which involved surgeries he personally performed. The remaining cases were managed by other surgeons using various techniques. Reported symptoms included pain, paresthesia, numbness (e.g., of the penis, thigh, buttocks, rectum, or vagina), urinary incontinence, and foot weakness with absent ankle reflex. Complete surgical removal of isolated cysts often led to full recovery, while patients with multiple cysts saw more limited improvement due to conservative surgical approaches. He concluded the monograph by urging increased clinical awareness of these lesions, stating that perineurial cysts may be a surgically treatable cause of sciatic and sacrococcygeal syndromes.
In his 1970 paper "Spinal Perineurial and Meningeal Cysts", Tarlov described the clinical features, diagnosis, and classification of spinal perineurial cysts, and distinguished them from other spinal cysts such as meningeal diverticula and intradural arachnoid cysts, which had often been conflated in earlier literature. He emphasized the importance of distinguishing these lesions to avoid unnecessary surgical interventions and diagnostic errors. Tarlov reported that perineurial cysts contained nerve root fibers and typically did not fill with contrast dye (Pantopaque) during initial myelography, although delayed filling may have been evident days or weeks later due to limited communication with the subarachnoid space. In contrast, meningeal diverticula do not contain nerve fibers, have free communication with the subarachnoid space, and usually fill immediately with contrast dye during myelography.
Signs and symptoms
Appearance Walls of Tarlov cysts are thin and fibrous; they are prone to rupture if touched, making surgery difficult. The nerve fibers embedded in the walls of the cysts have the appearance and size of dental floss; these nerve fibers are usually not arranged in any specific alignment."Donlin Long., The Johns Hopkins Hospital Dept. of Neurosurgery, interviewed by Hsuan Chen, Oct. 6th, 2009." Histologic examination reveals the Tarlov-cyst outer wall is composed of vascular connective tissue, and the inner wall is lined with flattened arachnoid tissue. In addition, part of the lining containing nerve fibers also occasionally contains ganglion cells. The cysts can contain anywhere from a couple of milliliters of CSF to over of CSF.
Location Tarlov cysts are most commonly located in the S1 to S4/S5 region of the spinal canal, but can be found along any region of the spine. Tarlov cysts typically form on the extradural portions of the sacral nerve roots, most often near the dorsal root ganglion of the dorsal (sensory) nerve roots. They arise within the perineural space, between the endoneurium and perineurium. Occasionally, these cysts are observed in the lumbar and thoracic spine. The cysts are often multiple, extending around the circumference of the nerve, and can enlarge over time to compress neighboring nerve roots, to cause bone erosion.
The cysts may also form on the anterior (front) side of the sacrum and have been known to extend into the pelvic cavity. These cysts, though rare, can be found to grow large - over in size, often causing severe pelvic pain from compression on the cyst itself as well as adjoining nerves. Tarlov Cyst Symptoms
+Reported Tarlov Cyst Symptoms According To The Involved Nerve Roots Nerve Supply Symptoms S2, S3, S4 Sensory: Perineum, clitoris, penis, vagina, scrotum
Autonomic: Detrusor muscle of the bladder, descending colon, transverse colon, internal urinary sphincter, internal anal sphincter
Motor: External Urinary sphincter, external anal sphincter Pelvic Pain
Perineal pain & paresthesia
Vaginal pain; dyspareunia
Testicular or penile pain; prostate pain
Pelvic instability symptoms
Neurogenic bladder symptoms: urine retention, hesitation, valsalva voiding, urinary frequency, urgency, painful bladder, urge incontinence, stress incontinence.
Neurogenic bowel symptoms: constipation, alternating with diarrhea; intestinal cramps; defecation frequency; urgency;bloating;false defecation urge, fecal incontinence; stabbing pain; pressure or cramps in anal sphincter
Erectile dysfunction; retrograde ejaculation
Female anorgasmia; persistent genital arousal disorder S2 Sensory: Perineum, posteromedial side of the legs, plantar region of the feet
Motor: Intrinsic foot muscles Pain, cramps, and paresthesia in the feet atrophy of the intrinsic foot muscles due to compression of nerve root S2 L5 and S1 Sensory: Posterior side of the legs (S1), lateral side of the leg, first and firth toe (L5), dorsal side of the feet
Motor: Gluteus maximus muscle and calf muscles (S1), gluteus medius muscle and extensor muscles of the feet and toes (L5) Lumbar and sacral pain
Pain in the piriformis muscle and trochanter region
Pain and/or paresthesia in the legs and feet
Leg cramps Leg weakness Neurogenic claudication: pain while walking, a significantly slower walking pace than before onset, increased pain when walking uphill Weakness of dorsiflexion of the feet; rarely foot drop (L5) Weakness of plantar flexion of the feet (S1) L1 to L4 Paresthesia and pain in the legs Weakness of knee or hip extension Thoracic nerve roots Paresthesia and pain in the upper back Intercostal neuralgiaCervical nerve roots Cervical pain and pain in the trapezius muscles Pain and paresthesia in the arms and handsBrain Headaches
Symptoms Pain Paresthesia Spasticity, Hypertonia Muscular Dysfunction or Weakness Radiculopathy