Study Design. A retrospective case study of patients with intraspinal cyst having a distinct connection with the corresponding intervertebral disc. Objectives. To propose a new clinical entity, "discal cyst," by clarifying the clinical, radiographic, and histologic aspects of the disease. Summary of Background Data. Several types of intraspinal cysts with different pathogenesis, causing symptoms indistinguishable from those of lumbar disc herniation, have been reported, such as perineural cysts, synovial cysts, and ganglion cysts. However, to the authors' knowledge, no detailed analysis has been made of cysts that have a distinct connection with the corresponding intervertebral disc. Methods. Clinical pictures, radiographic findings, and surgical and histologic findings in eight surgically treated patients with intraspinal cyst having a distinct connection with the intervertebral disc were reviewed. Possible pathogenesis and a proposal for nomenclature were also discussed. Results. This disease can be characterized by (1) clinical symptoms indistinguishable from those of typical disc herniation, manifesting as a unilateral single nerve root lesion; (2) incidence at slightly younger age and at upper intervertebral levels than with typical disc herniation; (3) T1 low signal and T2 high signal intensity, round to oval mass lesion on magnetic resonance imaging, compatible with a liquid-containing cyst; (4) minimal degeneration of the involved disc, either on discography/computed tomographic discography or magnetic resonance imaging; (5) a connection between the cyst and the corresponding intervertebral discs on discograms with severe radiating pain in the affected leg at the time of injection; (6) immediate relief of symptoms after simple removal of the cyst; (7) cyst wall consisting of dense fibrous connective tissue containing bloody to clear serous discharge; and (8) absence of disc materials and a specific lining cell layer on histologic examination, Although the exact cause is unknown, underlying minor disc injury may serve as a basis for cyst formation. Conclusion. Eight cases of intraspinal cysts communicating with the intervertebral disc presenting symptoms identical to those of disc herniation are presented. Because all cysts were connected to the corresponding disc and the development of the cyst was assumed to be related to underlying disc injury, it is proposed to name-this clinical entity discal cyst.
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