Tarlov Cyst Information
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Definition and Description
Tarlov cysts (hereafter referred to as TCs) are also known as perineural/perineurial, or sacral nerve root cysts. They are dilations of the nerve root sheaths and are abnormal sacs filled with cerebrospinal fluid (hereafter referred to as CSF) that can cause a progressively painful radiculopathy (nerve pain). They are located most prevalently at the S2, S3 level of the sacrum. The sacrum is a fused triangle-shaped bone comprised of the five sacral vertebrae forming the base of the spine. The five lumbar vertebrae are located just above the sacrum, and the four coccygeal vertebrae are just below the sacrum forming the coccyx or tailbone.
Perineural cysts can form in any section of the spine; a significant percentage (11%) of patients have cysts at more than one location of the spine.. Some patients have cysts at all sections of the spine, including cervical, thoracic, lumbar, and sacral. Other very closely related spinal pathology and symptoms can be due to meningeal diverticulum, meningocele, and pseudomeningocele.
The TCs appear on MRI to be dilated or ballooned areas of the sheaths that cover nerve roots exiting from the sacral region of the spinal column. The cysts are created by the dilated sheaths of the nerve roots directly connected to the subarachnoid area of the spinal column, through which the cerebrospinal fluid flows. There are 3 layers or meninges (coverings) of the brain and spinal cord. They are the dura mater, literally meaning “hard mother” in Latin, which is the outermost , toughest, and most fibrous of the three layers. Next is the arachnoid layer, the middle layer where the spinal fluid flows, and the innermost layer, the pia mater. The space between the arachnoid and pia mater layer is called the subarachnoid space.
Some individuals have TCs visible on a MRI, but have experienced no relevant symptoms, and the cysts are perhaps identified, but are not acknowledged as significant by the radiologist reading the films or by the physician who ordered them. If the patient has no symptoms that might be suggestive of symptomatic TCs, and sometimes even if they do have symptoms, the patient might not be told about the finding on the MRI. It is not unusual, if the cyst has been present for a number of years to see evidence of erosion and remodeling of the sacral bone, or other vertebrae in the spine. When conditions cause these cysts to fill with more spinal fluid and to expand in size, they begin to compress important surrounding nerve fibers; the cysts contain nerve fibers, resulting in a variety of symptoms including chronic pain.