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Tarlov cysts, also known as perineural cysts, are type II innervated meningeal cysts, cerebrospinal-fluid-filled (CSF) sacs most frequently located in the spinal canal of the S1-to-S5 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.〔Goyal RN, Russell NA, Benoit BG, Belanger JM. Intraspinal cysts: a classification and literature review. ''Spine'' 1987;12:209-213〕 Since Tarlov cysts are cysts of the spinal meninges, symptomatic Tarlov cysts by definition cause myelopathy. The etiology of these cysts is not well understood; some current theories explaining this phenomenon have not yet been tested or challenged but include increased pressure in CSF, filling of congenital cysts with one-way valves, inflammation in response to trauma and disease. They are named for neurologist Isadore Tarlov, who described them in 1938.〔(Tarlov Cyst and Infertility ); by Pankaj Kumar Singh, with Vinay Kumar Singh, Amir Azam, and Sanjeev Gupta; in J Spinal Cord Med. (archived at the National Institute of Health) Apr 2009; 32(2): 191–197; retrieved March 11, 2014〕 Tarlov cysts are relatively common when compared to other neurological cysts. Initially, Isadore Tarlov believed them to be asypmptomatic, however as his research progressed, Tarlov found them to be symptomatic in a number of patients. These cysts are often detected incidentally during MRI or CT scans for other medical conditions. They are also observed used magnetic resonance neurography communicating subarachnoid cysts of the spinal meninges. Cysts with diameters of 1cm are 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. 〔Nishiura I, Koyama T, Handa J: "Intrasacral perineural cyst." Surg Neurol 23:265 269, 1985〕 Current treatment options include CSF aspiration, complete or partial removal, fibrin-glue therapy, laminectomy with wrapping of the cyst, amongst 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 Marfan syndrome, Ehlers-Danlos syndrome, and Loeys-Dietz syndrome. == Classification == Tarlov cysts are considered Type II lesions, being defined as extradural meningeal cysts with nerve fibers.〔Nabors MW, Pait TG, Byrd EB, et al. Updated Assessment and Current Classification of Spinal Meningeal cysts. ''J Neurosurg.'' 1988;68:366-377〕 Nabors et al. classify Arachnoïd cysts into three types: * Type I : Extra-dural; no nerve roots or rootlets such as intra-sacral meningoceles; probably of congenital origin developing from the dural sac to which they are connected by a little collar. They are found at the point of exit of a dorsal nerve root from the dural sac. They are sometimes difficult to identify and can be "seen" as a type II cyst on imaging. These cysts are often associated with foramina enlargement and scalloping of the vertebrae. It is very important to distinguish them from sacral meningoceles going to the pelvic area; they are often associated with other congenital abnormalities ( teratomes, dermoïdes, lipomes, and other abnormalities( uro-genital and ano-rectal)) * Type II: Extra-dural; nerve root present (such as Tarlov or perineural cysts). There are often not only one but multiple cysts, mostly found in the sacrum area. There are two types: Tarlov (perineural) cysts are located posteriorly to the root ganglion, with nerve fibres inside or nerve tissue in the walls; they are not communicating with the perineural arachnoid space. Type-II cysts are very small in the upper sacral area, but can be bigger (up to ) if found located in the lower part of the sacrum. The second variant of type-II cysts are called "meningeal diverticuli". They are located anteriorly to the nerve root ganglion, with nerves fibres inside and communicating with the subarachnoid space. * Type III: intra-dural; these are either congenital or caused by trauma; they are rarely associated with other abnormalities and rare in occurrence. About 75% can be found in the dorsal area. Most of the congenital type-III cysts can be found posteriorly to the spinal cord, as opposed to those caused by trauma which can be found anteriorly to the spinal cord.〔〔Singh, P. K., Singh, V. K., Azam, A., & Gupta, S. (2009). Tarlov Cyst and Infertility. Journal of Spinal Cord Medicine, 32(2), 191-197.〕 Post trumatic inflammation induces cavitation and cystic formation and leads to greater secondary CNS injury. 〔 〕Cellular migration causing these cyst cavities was observed both in vitro and in vivo and cavitation was observed to be prevented with the use of an anti-inflammatory. Further more migration inflammatory cells into traumatized tissue has been observed with inflammation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tarlov cyst」の詳細全文を読む スポンサード リンク
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