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Dear Editor,Werecentlyencounteredadisccystina32-year-oldmanwithrefractory low back pain and radiation into the left L5dermatome since almost 1 year. MRI revealed a liquid-containingcystwithextensionintotheleftlateralrecessofL5and scalloping of the adjacent vertebral body (Fig. 1). Thisradiological sign is indicative of a long-standing process as itis the result of bone remodeling. The cyst caused dorsaldisplacement and significant compression of the thecal sacand left L5 root. The cyst was removed through a left L4hemilaminectomy. A small annular fissure on the L4–L5 discwas noted after cyst removal, and subsequently, a discec-tomy was performed. After surgery, the low back pain andsciatica disappeared. Histological examination of the cystwall exhibited chondrocytes and fibrillary stroma of discmaterial with areas of myxoid degeneration.Disc cysts (also known as discal cysts) are rare cysticlesions in the ventrolateral epidural space. Theyare located atL4–L5 more often thanat other lumbar levels, and they occurmostly in young men who present with refractory low backpain and sciatica. Disc cysts were first described one decadeago and distinguished from ganglion cysts of the posteriorlongitudinal ligament (PLL) by means of their cyst–disccommunication at discography [4]. Ganglion cysts of thePLL [7] and disc cysts differ from juxtafacet cysts [10]byvirtue of a ventral location, an intimate or pedicledattachment to the annulus fibrosus or PLL, and absentconnection with a degenerative facet joint. Unlike juxtafacetcysts, disc cysts and ganglion cysts of the PLL are bothwalled-in by fibrous connective tissue without a synoviallining and frequently show myxoid degeneration. Chondro-cytes could be demonstrated in the cyst wall of our case andin only a very few other disc cysts reported in the literature[9]. Because of the clinical, radiological, surgical, andhistological similarities between disc cysts and ganglioncysts, Marshman et al. [6] suggested that their distinction onthe basis of disc space communication is unnecessary. Forthe same reason, they also proposed to use the term “disccyst” for both disc cysts and ganglion cysts of the PLL.Discography is an invasive diagnostic procedure inwhich radiopaque contrast medium is injected into thenucleus pulposus. In disc cysts, this technique can be usedto assess disc–cyst communication and to reproduceradiating pain into the affected leg [8]. As explained above,disc–cyst communication at discography was originallyemployed as a means to distinguish disc cysts fromganglion cysts of the PLL. Nevertheless, discography wasnot used in nearly all of the reported ganglion cysts of thePLL, and the same is true for some reports on disc cysts [2,3, 5]. The reason is that patients were either treatedconservatively [2, 3] or the disc–cyst communication wasevaluated surgically [5]. This can be achieved by directvisualization of a connection between the cyst and itscorresponding disc or by observation of a defect in theannulus fibrosus after cyst removal [6, 8]. The onlyremaining importance of disc–cyst communication lies inthe fact that its presence is generally regarded as anindication for discectomy in addition to cystectomy. |
