Diagnosis and Management of Sacral Tarlov Cysts

Frank L. Acosta, Jr.; MD, Alfredo Quinones-Hinojosa, MD; Meic H. Schmidt, MD; Philip R. Weinstein, MD

Disclosures

Neurosurg Focus. 2003;15(2) 

In This Article

Discussion

Definition and Classification of Tarlov Cysts

Tarlov's original description of perineurial cysts was reported in 1938 and based on observations made during dissection of 30 cadaveric terminal filum specimens at the Montreal Neurological Institute.[39] He noted extradural cysts, often multiple, on portions of the posterior sacral and coccygeal nerve roots in five of these specimens. On histological examination, he found that these cysts were located in the perineurial space, between the endo-and perineurium at the junction of the posterior nerve root and its ganglion. These lesions either surrounded the entire nerve root or invaded it and became surrounded by compressed nerve fibers. Based on this and later studies, Tarlov[38,39,41] distinguished perineurial cysts from meningeal diverticula on the basis of three main findings ( Table 1. ). First, Tarlov cysts have a potential, but not an actual, communication with the spinal subarachnoid space and thus may exhibit delayed filling or lack of filling on myelographic examination. Meningeal diverticula, on the other hand, are in free communication with the spinal subarachnoid space and thus usually fill initially during myelography. Second, Tarlov cysts occur at or distal to the junction of the posterior nerve root and the DRG, usually in the sacral region. In comparison, meningeal diverticula occur proximal to the DRG and develop throughout the vertebral column, most often at thoracic levels. Last, Tarlov cysts occur in the perineurial space and have at least part of their wall composed of nerve fibers or ganglion cells. Conversely, meningeal diverticula have a wall lined with arachnoid mater, with or without a dural covering, and do not contain nerve fibers. Moreover, Tarlov noted that perineurial cysts, although often asymptomatic, were capable of producing clinical symptoms, whereas meningeal diverticula were more often asymptomatic. Tarlov[41] also distinguished perineurial cysts from "unusually long arachnoidal prolongations over nerve roots," which he asserted were of no pathological significance.

Despite Tarlov's efforts, a great deal of confusion continues to exist over the precise definition of Tarlov cysts and their distinction from other spinal cysts. Tarlov cysts have been referred to as perineurial cysts,[7,37,38,39,40,41,45,46] "nerve root diverticula",[35] meningeal cysts,[23] sacral cysts,[31,32] arachnoid cysts,[27,28,29] and arachnoid pouches.[13] Two recent classifications have been described in an effort to standardize cyst-related nomenclature and diagnosis ( Table 2. ).[9,17] Goyal, et al.,[9] classified intraspinal cysts according to five categories: 1) perineurial or Tarlov cyst (Strully nerve root diverticulum[35] ); 2) nerve root sleeve dilation, 3) intradural arachnoid cyst; 4) extradural arachnoid cyst; and 5) traumatic nerve root cyst. More recently, Nabors, et al.,[17] divided spinal meningeal cysts into three categories: Type I or "extradural meningeal cysts without spinal nerve root fibers"; Type II or "extradural meningeal cysts with spinal nerve root fibers" (that is, Tarlov cysts); and Type III or "spinal intradural meningeal cysts." These authors noted that CT myelography usually demonstrated that both Tarlov cysts and spinal nerve root diverticula have a communication, albeit delayed, with the spinal subarachnoid space, and are actually the same lesion. Thus, CT myelography has enhanced our understanding of Tarlov cysts and has led to a revision of Tarlov s original hypothesis that perineurial cysts do not communicate with the subarachnoid space. However, CT scans must be obtained with the lumbosacral spine in dependent position and delayed 30 to 60 minutes after subarachnoid contrast injection to avoid missing a microscopic communication. Regardless of the nomenclature or classification system, the defining feature of Tarlov perineurial cyst is the presence of spinal nerve root fibers within the cyst wall or within the cyst cavity itself.[9,17,37 41] Thus, although CT myelography and MR imaging are useful tools, the final diagnosis of a Tarlov cyst is not a radiological one; rather, it is a histopathological one.

Signs and Symptoms of Tarlov Cysts

In his original description,[39] Tarlov noted that perineurial cysts developed in asymptomatic patients, although he later speculated that these cysts could cause sacral radiculopathy when he noted that resection of a cyst relieved one woman of sciatic pain.[37] Although they most often affect S-2 and S-3 nerve roots,[32] Tarlov cysts have been found to occur anywhere in the cervical, thoracic, and lumbar spine.[8,12,17,19,22,32,36,40,41] Most are diagnosed as incidental findings on CT or MR imaging. Approximately one fifth of Tarlov cysts are symptomatic and can produce, according to their anatomical location,[16] a variety of symptoms of nerve root compression ( Table 3. ). Sacral cysts have been noted to cause sacral radiculopathy, hip, leg, or foot pain, perineal pain, paresthesias, and bowel or bladder dysfunction.[1,2,5,7,18,24,30 32,35 38,40,41,46] Symptoms can be exacerbated by standing, coughing, or other Valsalva maneuvers, because elevated subarachnoid pressure forces CSF from the spinal subarachnoid space through a small ball valve like communication into the perineurial cyst cavity.[16,36] Tarlov cysts may also cause diffuse poorly localized sacral pain due to pressure on adjacent periosteum and joint capsules and can also result in sacral insufficiency fractures from erosion of the sacrum.[9,25] Thoracic Tarlov cysts have even been noted to cause angina-like symptoms.[11]

Tarlov cysts can also cause various objective neurophysiological abnormalities, including decreased sural nerve action potentials and sensory nerve conduction velocities.[5,46] Tarlov cysts cause mostly sensory disturbances, because of their location at the DRG. Accordingly, motor nerve conduction is often normal in patients harboring these cysts.[5] Bladder dysfunction can be documented by cystometrographic studies, and sexual impotence was observed in our previous series.[16]

Radiological Features

Tarlov cysts are associated with a variety of radiological findings. Initial plain radiographic examination may reveal Tarlov cysts causing erosion of the sacrum, bone scalloping, or a rounded paravertebral shadow.[1,6,14,32,35,41] Schrieber and Haddad[31] were the first to demonstrate that Tarlov cysts exhibited a characteristic delayed filling pattern on oil-based pantopaque contrast enhanced myelography. This pattern, in which Tarlov cysts do not immediately fill with oil-based contrast but can later be visualized hours, days, or weeks later to contain contrast, has since been described by several authors,[20,31 33,35,36,41] and was one of the criteria used by Tarlov[41] to distinguish perineurial cysts from meningeal diverticula. Because Tarlov cysts have only a potential, or very small communication with the subarachnoid space, the visualization of the cyst cavity on myelography occurs as a result of a much slower process in which contrast is forced, via the hydrostatic pressure of CSF, from the subarachnoid space through this small aperture or by transudation across the cyst wall membrane, into the perineurial cyst cavity.[41] Meningeal diverticula, on the other hand, having a relatively greater communication with the spinal subarachnoid space, can be seen to fill with oil-based contrast immediately after injection during myelography.[41] Tarlov cysts can, however, often be seen to fill more rapidly on myelography with lower viscosity water-soluble contrast materials (metrizamide).[20,21,41] The authors of other studies have found Tarlov cysts to have no communication with the spinal subarachnoid space, thus only producing an extraarachnoid filling defect on myelography.[1,32,45]

Computerized tomography scanning, both with and without intrathecal contrast material, has enhanced our ability to detect perineurial cysts. These lesions are iso-dense with CSF on noncontrast CT scans[21,45] and can often be seen to cause various osseous abnormalities and erosions.[7,33] Postmyelography CT scanning is effective in demonstrating the presence of a communication of the cyst with the spinal subarachnoid space, and it can also demonstrate surrounding sacral bone scalloping.[16]

Because of the absence of interference from bone, enhanced resolution of tissue density, and its multiplanar imaging capabilities, MR imaging is particularly useful in studying sacral Tarlov cysts, thus, it is considered to be the preferred initial imaging modality when a sacral perineurial cyst is suspected.[24,30] These cysts have CSF-like characteristics on MR imaging that is, a low signal on T1-weighted images and a high signal on T2-weighted images.[24] Magnetic resonance imaging can also be used to delineate the exact relationship of the cyst to the thecal sac, as well as the total volume of fluid within the cyst.[23] It may also demonstrate bone and pedicle erosion, sacral canal widening, and neural foramina enlargement.[24] The senior author[16] (P.R.W.) and others[17] have recommended MR imaging for initial identification of a spinal cystic mass, followed by CT myelography for further delineation of cyst characteristics ( Table 3. ).

Origin and Pathogenesis of Tarlov Cysts

In his original description, Tarlov[39] discovered inflammatory cells in some cyst walls and adjacent tissues, leading him to postulate that these cysts were formed by a process of inflammation within the nerve root sheath, followed by inoculation of fluid. He later noted that pantopaque contrast could initiate an inflammatory process that sealed off communication between an asymptomatic meningeal diverticulum and the subarachnoid space, creating a symptomatic perineurial cyst.[41] He also described changes consistent with ischemic degeneration in some cysts.[39] A hemorrhagic origin was later described by Tarlov[37,40,41] and others[31,43,44] in which cyst formation occurs as a result of infiltrating subarachnoid hemorrhage, or traumatic intraneural hemorrhage, followed by cystic degeneration of red blood cells and destroyed neural tissue. Nishiura, et al.,[20] described a history of antecedent trauma in 40% of their patients with Tarlov cysts. Schreiber and Haddad[31] and Strully and Heiser[36] noted that cysts can form as a result of dural lacerations during spinal surgery, leading to pseudomeningocele formation. Some authors favor a congenital origin and hypothesize that these cysts can arise from a congenital dural diverticulum or weakness, or from persistent embryonic fissures.[12,22,35] Tarlov cysts have been associated with other congenital abnormalities, connective tissue disorders, and nerve root sheath duplications.[3,8,10,14,19,27,42] Rexed alone[28] and with Wennstrom[29] argued that the cysts occur as a result of proliferation of arachnoid mater, followed by a closure of the communication between the arachnoid proliferations and the spinal subarachnoid space. Finally, some authors have ascribed the hydrostatic pressure of CSF as the causative factor in cyst formation.[24,34,35] They argued that the hydrostatic pressure of CSF is exerted along the spinal subarachnoid space and is elevated with arterial pulsations or Valsalva maneuvers. This acts to force CSF into the normally obliterated perineurial space, while outflow is restricted because of a ball-valve effect. Cysts subsequently enlarge by means of this mechanical pulsatile CSF action, and become symptomatic by displacing adjacent nerve roots.[22,24]

Natural History and Treatment of Symptomatic Tarlov Cysts

Although most remain asymptomatic throughout the patient s life, the natural history of symptomatic Tarlov cysts is one of progressive enlargement leading to increasing symptoms. The hydrostatic and pulsatile forces of CSF cause Tarlov cysts to grow over time. As the mass enlarges, sensory nerve root filaments are stretched over the periphery of the lesion or are compressed against adjacent bone or other nerve roots, causing pain or other sensory disturbances.[2,30,35,41]

There is no consensus on the optimal management of symptomatic Tarlov cysts. Nonsurgical methods include lumbar CSF drainage to decrease the hydrostatic pressure and therefore the pressure within the cyst cavity.[2] Symptoms do recur, however, after drainage is stopped.[2] In one case the authors found that continuous CSF drainage via a lumboperitoneal shunt was an effective therapy for symptomatic Tarlov cysts in each of two patients.[2] Some authors have asserted that by providing temporary symptomatic relief, lumbar CSF drainage can be a useful diagnostic tool when there is a question about the clinical significance of Tarlov cysts.[2,4]

Another nonsurgical treatment is percutaneous cyst drainage.[23,24] Symptoms do recur after percutaneous drainage because cysts reform, although the authors of one study asserted that percutaneous cyst aspiration and fibrin glue placement can prevent the recurrence of both the cyst and its associated symptoms.[23] In this study, 75% of the patients developed postprocedural aseptic meningitis. As a result of these findings, some authors have argued that there is no place for percutaneous cyst drainage in the treatment of these lesions.[11,42]

Surgical treatment of symptomatic perineurial cysts, involving complete cyst removal, and excision of the affected posterior root and ganglion, was advocated by Tarlov[37,38,41] and has since been used by others,[20] although some assert that the morbidity resulting from neurological defects following this procedure is too great to justify its use, especially when dealing with multiple bilateral sacral cysts.[4,44] Simple decompressive laminectomy has been attempted,[33] but its success rate has been low.[4] Other surgical therapies include cyst resection at the neck,[4,42] cyst wall resection,[38,41,42] cyst fenestration and imbrication[4,16,36,46] and cyst shrinkage by using bipolar cautery.[30] One author described the surgical placement of a cyst subarachnoid shunt tube to equalize pressures within the spinal subarachnoid space and the cyst cavity.[15] In our experience good results have been obtained with micro-surgical cyst fenestration and imbrication when using electrophysiological monitoring, along with a fat-or muscle graft reinforced cyst closure.[16] In a study conducted at our institution, seven of eight patients experienced improvement in symptoms. Bladder control improved in two of three patients with bladder dysfunction treated with cyst fenestration and imbrication. There were no postoperative complications.[16] In the present case, cyst imbrication was not performed because CT myelography revealed no direct communication with the spinal subarachnoid space. We instead performed microsurgical cyst fenestration and cyst wall resection with myocutaneous flap closure reinforcement to prevent a reaccumulation of CSF or a cyst recurrence. Cyst wall resection may result in postoperative neurological deficits[42] and should be performed during electrophysiological monitoring to minimize damage to sacral nerve roots.

Indications for Surgery

The authors of one study found that patients with Tarlov cysts greater than 1.5 cm and with associated radicular pain or bowel/bladder dysfunction benefit most from surgery.[42] We have recommended that patients presenting with radicular pain referable to the location of a cyst should initially undergo medical treatment with antiinflammatory drugs and physical therapy. Surgery should be reserved for that subset of patients in whom these conservative measures elicit no response. We have also found that patients presenting with symptoms exacerbated by postural changes or Valsalva maneuvers, as was true in the present case, are likely to benefit most from surgery.[16]

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