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|Classification and external resources|
MRI image showing a Tarlov cyst.
|This article needs attention from an expert on the subject. (April 2010)|
|Classification and external resources|
MRI image showing a Tarlov cyst.
Tarlov cysts, also known as perineurial cysts, are cerebrospinal-fluid-filled (CSF) sacs located in the spinal canal of the S1-to-S4 region of the spinal cord (much less often in the cervical, thoracic or lumbar spine), and can be distinguished from other meningeal cysts by their nerve-fiber-filled walls. Tarlov cysts are defined as cysts formed within the nerve-root sheath at the dorsal root ganglion. The etiology of these cysts is not well understood; some current theories explaining this phenomenon have not yet been tested or challenged.
Tarlov cysts are relatively common when compared to other neurological cysts, but they are usually asymptomatic. These cysts are often detected incidentally during MRI or CT scans for other medical conditions. Cysts with diameters of over 1.5 cm (0.6 in) are more likely to be symptomatic; surgical treatment should be considered if all other symptom-relieving options have been exhausted. No current treatment so far has proven to be effective due to the unclear pathogenesis and pathophysiology of Tarlov cysts. Current treatment options include CSF aspiration, complete or partial removal, fibrin-glue therapy, amongst other surgical treatment approaches.
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. 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 2.5 litres (0.5 imp gal; 0.7 US gal) of CSF.
Tarlov cysts are primarily located in the S1 to S4 region of the spinal cord. They usually form on the extradural components of sacrococcygeal nerve roots at the junction of dorsal root ganglion and posterior nerve roots and arise between the endoneurium and perineurium. Occasionally, these cysts are observed in the thoracic spine. However, these cysts most commonly arise at the S2 or S3 junction of the dorsal nerve root ganglion. 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 be found anterior to the sacral area and have been known to extend into the abdominal cavity. These cysts, though rare, can be found to grow large - over 3–4 centimetres (1.2–1.6 in) in size, often causing severe abdominal pain from compression on the cyst itself as well as adjoining nerves.
The following table is compilation of some key differences between Tarlov cysts, meningeal cysts, and arachnoid diverticula cysts. Although the definitions for each entity are still controversial, the following items are generally accepted.
|Tarlov Cyst||Meningeal Diverticula & Arachnoid Diverticula|
|Potential communication with spinal subarachnoid space||Communicates freely with spinal subarachnoid space|
|Delayed filling in myelograms||Rapid filling in myelograms|
|Found distal to the junction of posterior nerve root and dorsal root ganglion in sacral region||Found proximal to dorsal root ganglion throughout vertebral column|
|Walls contain nerve fibers||Walls lined by arachnoid mater with no signs of neural element|
|Often multiple, extending around the circumference of nerve root||No pattern of formation in regards to multiplicity|
Tarlov cysts are often asymptomatic; the cases of reported symptomatic Tarlov cysts ranges from 15% to 30% of the overall reported Tarlov cyst case, depending on the source of literature. Nevertheless, these cysts are important clinical entities because of their tendency to increase in size over time, potentially causing complications and eroding the surrounding bone tissue. Patients with symptomatic Tarlov cysts can be divided into 4 categories, according to their experienced symptoms:
Below are a list of commonly reported symptoms associated with Tarlov cysts:
Back pain, perineal pain, Sciatica, Cauda equina syndrome, dysuria, urinary incontinence, coccygodynia, sacral radiculopathy, radicular pain, headaches, retrograde ejaculation, paresthesia, hypesthesia, motor disorders in lower limbs and the genital, perineal, or lumbosacral areas, sacral or buttocks pain, vaginal or penile paraesthesia, sensory changes over buttocks, perineal area, and lower extremity; difficulty walking; severe lower abdominal pain.
There are several hypotheses proposed regarding the formation of Tarlov cysts, including: inflammation within the nerve root cysts followed by inoculation of fluids, developmental or congenital origin, arachnoidal proliferation along and around the exiting sacral nerve root, and breakage of venous drainage in the perineuria and epineurium secondary to hemosiderin deposition after trauma. Tarlov himself theorized that the perineurial cysts form as a result of blockage of venous drainage in the perineurium and epineurium secondary to hemosiderin deposition, after local trauma. Another theory gaining increasing popularity, over the past decade, is one postulated by Fortuna et al.; it described perineurial cysts to be the results of congenital arachnoidal proliferation along the exiting sacral nerve roots. The cause of these cysts is still unknown, and the proposed theories have not been tested or challenged.
Tarlov cysts are known to have the tendency to enlarge over time. The prominent theory that explains this phenomenon reasons the enlargement of the cysts is due to the cerebrospinal fluid being pushed into the cyst during systole pulsation, but unable to get out during the diastole phase, resulting in enlargement over time. However, this theory has yet to be tested. Although growth in the cysts occur, it is still unknown how often, or at what condition, these cyst form, or if any underlying condition is essential for the formation and enlargement of these cysts.
Many patients have been diagnosed for 20 years, showing a very thin sacrum bone "protecting" a large meningeal cyst. MRIs regularly made do not show any enlargement or any change. The "erosion" theory might be a simplification in regard of the life of a bony structure. Another view involves the shape of the bone, according to the fact that between the bone and the cyst strong and solid ligaments exist, and that the walls of the cysts are very fragile compared to ligaments and bones, when looking "eroded" means a congenital cyst or that was formed before the person was about 25 years old. There are many people who have cysts and no remodelling of the bone: neuroradiologists tell that those are due to a cause which took place when older than 25 years.
Bone Development and Structure
Because bone is made up of minerals, mostly hydroxyapatite, and is hard, many people think that it is not living material. But a bone in a living animal consists of both living tissue and non-living substances. Within the "alive bone" are blood vessels, nerves, collagen, and living cells including:
In addition, bone contains cells called osteocytes, which are mature osteoblasts that have ended their bone-forming careers. These cells engage in metabolic exchange with the blood that flows through the bones. The nonliving, but very important, substances in bone are the minerals and salts. Besides the metabolically active cellular portion of bone tissue, bone is also made up of a matrix (a bonding of multiple fibers and chemicals) of different materials, including primarily collagen fibers and crystalline salts. In particular, it is the collagen fibers and the calcium salts that help to strengthen bone. In fact, the collagen fibers of bone have great tensile strength (the strength to endure stretching forces), while the calcium salts, which are similar in physical properties to marble, have great compressional strength (the strength to endure squeezing forces). These combined properties, plus the degree of bondage between the collagen fibers and the crystals, provide a bony structure that has both extreme tensile and compressional strength.
Thus, bones are constructed in exactly the same way that reinforced concrete is constructed. The steel of reinforced concrete provides the tensile strength, while the cement, sand, and rock provide the compressional strength. However, the compressional strength of bone is greater than that of even the best reinforced concrete, and the tensile strength approaches that of reinforced concrete. But, even with their great compressional and tensile strengths, neither bone nor concrete has a very high level of torsional strength (the strength to endure twisting). In fact, bone fractures often occur as a result of torsional forces that are exerted on an arm or a leg.
Many authors state that the blood, and breakdown products, acting as a foreign-body substance in the subarachnoid space, produce local adhesive arachnoiditis with no symptoms but can also create cystic degeneration. The subarachnoid space abhors all foreign body substances. Even the presence of injected air is considered to be a "foreign body." Blood is definitely considered a foreign body (particularly the breakdown products of blood). Repeated exposure to foreign-body substances in the subarachnoid space can initiate auto-immune amnestic reactions which may potentiate and magnify the ongoing inflammatory process.
Few clinicians appreciate that significant pathologic change can occur unaccompanied by clinical symptoms because of the body's remarkable ability to adjust to, and compensate for, slowly occurring insult. This is particularly true of nervous system which does not respond well to acute change or acute insult (i.e. sudden trauma, acute intracranial haemorrhage or acute rupture of an aneurysm). The ability of the body to compensate is an important reason why most individual afflicted with adhesive arachnoiditis have few in the way of clinical symptoms. This state is, however, a tenuous one, which can change dramatically with only minimal additional insult, mostly when the individual is also afflicted of meningeal (arachnoid or Tarlov cysts).
It is unusual for patients to experience, as a complication of spinal tap, continued leakage of cerebrospinal fluid producing postural headache, light-headedness and inability to function due to these complaints. The commonly employed treatment for this is a "blood patch". Blood drawn from a vein is purposely injected into the supposed epidural space as a means of "patching" the leaking fluid.
Appropriate blood patches routinely introduce some blood into the subarachnoid space and inappropriate ones may introduce as much as 10-12cc of blood directly into the subarachnoid space. How much blood, introduced how often, is necessary to create adhesive arachnoiditis? This question has not yet been answered. We only know at this point in time, that blood, and its breakdown products, can serve to create adhesive arachnoiditis and the introduction of any foreign body substance (for any purpose) into the subarachnoid space is not a wonderful idea.
Not to forget to mention that arachnoïd cysts, meningeal cysts are very frequently induced by a dormant Arachnoïditis and that only that area of the spine, where the “cysts” are can be the cause for neuropathic pain and a limitation of functions syndrome.( Charles Burton-The Burton report http://www.burtonreport.com/, Dr Sarah Fox http://www.theaword.org/,Dr Aldrete - Arachnoïditis: The evidence revealed jan.2010, editorial Allil ISBN 978-607-7504-25-2)
Two most commonly used and effective examination method for Tarlov Cysts are MRI and CT. Both CT and MRI are good imaging procedures that allow the detection of extradural spinal masses such as Tarlov cysts. In fact, most of the cysts are asymptomatic and are found incidentally during CT or MRI examinations for other reasons.
MRI, or Magnetic Resonance Imaging, is considered the imaging study of choice in identifying Tarlov cysts. MRI provides better resolution of tissue density, absence of bone interference, multiplanar capabilities, and is noninvasive. Plain films may show bony erosion of the spinal canal or of the sacral foramina On MRI pictures, the signal is the same as the CSF one.
If MRI made with a contrast medium:
A computed tomography (CT) scan is another examination method often used for the diagnosis of Tarlov cyst. Unenhanced CT scans may show sacral erosion, asymmetric epidural fat distribution, and cystic masses that are have the same density with CSF. CT Myelogram is minimally invasive, and could be employed when MRI cannot be performed on patient.
The term "Tarlov cysts" (or "sacral perineurial cyst"), has often been misused for referring to other cystic lesions in the sacral region. Tarlov cysts are often detected through MRI or CT Myelography; these tools are very useful in spotting cysts at the region, but they cannot distinguish one major difference between Tarlov cysts and other cysts: the fact the walls contain nerve fibers. Therefore, the final diagnosis of a Tarlov cyst is not a radiological but rather, a histopathological, diagnosis  These cysts are sometimes also misdiagnosed as lumbar disc herniation or lumbar spinal stenosis, especially when they are pressing on the S-1 nerve root.
Because of the unclear pathogenesis and pathophysiology of Tarlov cysts, there is no consensus on the optimal treatment of symptomatic sacral perineurial cysts. There are a few treatments available for alleviating the symptoms caused by these cysts, but their effectiveness is debatable. Therefore, operative criteria for regarding Tarlov cysts include: 1) MRI results indicating the existence of sacral perineurial cyst; 2) the diameter of cyst is more than 1.5 cm or 0.6 inch; 3) neurological symptoms and signs attributed to sacral perineurial cysts that are serious enough to warrant treatment; 4) no or little response to medical and physical therapy, and 5) no contraindications for the surgery. The two major treatment types are the extraction of cerebrospinal fluids from the cyst, and the complete/partial removal of cyst from an infected area. But because the cyst walls are lined with nerves, this may not be an option. The morbidity has been seen to be higher on patients that have bilateral cysts on the same spinal level. It had been reported that a positive filling defect and larger cyst size (>1.5 cm or 0.6 inch) is a good indicator for successful treatment outcome. Although fibrin-glue therapy had been proven to be a promising therapy in the treatment of these cysts, there have been cases of the fibrin seeping back up into the spine, affecting other nerves. It is not recommended for use at present by the Health Department in some countries. Nevertheless, all types of surgical treatment pose common risks, including neurological deficits, infection and inflammation, spinal headache, urinary disturbances, and leakage of cerebrospinal fluids.