CT & MRI: Fluid like signal intensity lesion, left L4-5 with downward extension, left thecal compression and lateral recess stenosis, suspicious extension from L4-5 disc, with disc degeneration.

 Discography & CT-Discography: Anular fissuring at L4-5, left centrally, and contrast filling in the lesion through thin tract

 CT-guided asp. ( with 22G needle): Bloody like thin fluid was asp. (about 2cc)

After aspiration, lesion was shrunken on MRI.

Differential Diagnosis:

 1)Intraspinal extradural cysts, such as Perineural cyst, Synovial cyst, Ganglion cyst, Pseudocyst, Ligamentum flavum cyst,etc.

 2) Epidural varices, premembraneous hematoma

 3) Metastatic tumor and chondroma

Diagnosis:  Discal cyst, left L4-5 (on MRI, Discogram, CT- discogram and Asp.)

Dicussion:

 It is proposed to name this clinical entity Discal cyst in 1997 by Japanese Orthopedic surgeons.

Characteristic findings are

1)      Clincal 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)      Low SI on T1WI, high SI on T2WI, round to oval mass lesion on MRI, compatible with a liquid-containing cyst

4)      Minimal degeneration of the involved disc, either on discography/CT discography or MRI

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

8)      Absence of disc materials and a specific lining cell layer on histologic examination

Pathogenesis;

Underlying intervertebral disc injury and minor forces generated by excessive movement of the spine may be responsible for the development of these cysts. (Thereby leaving a communication with the corresponding disc, which was detected in all cases). : Similar to a meniscal cyst, -- proposed this clinical entity be called a ‘Discal cyst’.

Treatment: Simple removal, or Image-guided percutaneous aspiration. (spontaneous regression: rare)

References:
1.  Intraspinal cysts: A Classification and literature review. Goyal RN, Russel NA, Benoit BG, et al. Spine 1987;12:209-213
2. Three cases of intraspinal cyst whose symptoms resembled lumbar disc herniation. Nishizawa T, Koyanagi T, Toyama Y, et al. Seikeigeka 1995;46:1353-7(In Japanese)
3. Pathogenesis and diagnostic of intraspinal cyst communicating with intervertebral disc in the lumbar spine. Toyama Y, Kamata M, Matsumoto M, et al.  Rinsho, Seikei Geka 1997;32:393-400(In Japanese)
4. Intraspinal cyst communicating with the intervertebral disc in the lumbar spine: Discal cyst. Kazuhiro C, Yoshiaki T, Morio M, et al. Spine 2001;26:2112-2118
5. Spontaneous regression of an intraspinal disc cyst. Demaerel P, Eerens I, Goffin J, et al. Eur. Radiol.2001;11:2317-2318
6. Lumbar spine intracanalicular discal cysts: Two case reports. Michael FC, John RB. Journal of Spinal Disorders & Techniques 2002;15:431-435
7. Lumbar intervertebral disc cyst as a cause of radiculopathy: Case study. Gerard KJ, John AB. The spine Journal 2003;3:242-246
8. Percutaneous CT-guided Puncture and steroid injection for the treatment of lumbar discal cyst: A Case report. Hiroaki K, Kazunori Y, Takuya Y , et al. Spine 2003;28:E212-E216
9. Is Magnetic Resonance Image alone sufficient for detecting Disc cyst ?  Hong HJ, Yi HJ, Bak KH, et al. J Korean Neurosurg Soc 2004;35:328-331
10. Midterm results of percutaneous CT-guided aspiration of Symptomatic Lumbar Discal cysts. Kang HY, Liu WC, Lee SH et al. AJR 2008;190:W310-W314