Variation of a Disc Cyst in a 13-year-old girl - A case report

Introduction:

Lumbar radiculopathy can be caused by a wide spectrum of disease pathologies, the commonest being intervertebral disc herniation and lumbar canal stenosis. Less common causes include intraspinal extradural masses and cysts like disc cysts, perineural cysts, synovial cysts, and ganglion cysts.

Case report:

A 13-year-old girl presented with low back pain radiating to the right lower limb for six months following a fall from a bicycle. The pain was aggravated by standing and walking and relieved by lying down. Conservative measures did not provide significant relief of pain and she had lost considerable period from school. She had a prominent trunkal shift to the right side and the straight leg-raising test on the right side was restricted to 40 degrees. She had hamstring spasm on the right side with significant restriction of flexion and extension of the spine. She had no neurological deficit.

Plain radiographs of the lumbosacral spine revealed a loss of lumbar lordosis.

In view of the chronicity of symptoms, severe restriction of activity and failure of conservative measures, a surgical decompression was performed. The L5-S1 intervertebral space was exposed through a posterior midline approach. Through the microscope, a large central disc cyst was seen compressing the thecal sac and the traversing S1 roots.  There were no adhesions between the cyst and the dura. The content of the cyst was a colorless serous fluid, which leaked out following decompression leaving the nerve roots and thecal sac freely mobile without any compression. The disc space was thoroughly curetted but scanty disc material was obtained. Histopathological examination of the specimen obtained during surgery showed multiple areas of cystic degeneration without any specific lining cells. Following the surgery, the patient had significant relief of pain and was allowed to walk on the third post-operative day. She went on to have an uneventful recovery and was able to attend school.

MRI of the spine revealed a significant posterocentral disc protrusion at L5-S1 level. T1 hypointensity and T2 hyperintensity within the protruded disc and the parent disc suggested the presence of fluid. The cystic disc component was subligamentous with an intact outer annulus. Direct continuity between the disc and the cyst was noted.

Discussion:

Lumbar disc cysts are an uncommon cause of lumbar radiculopathy and closely mimic the clinical features of a disc herniation with a single root lesion. The ventral location of this intraspinal extradural cyst and the communication with the parent intervertebral disc separates this entity from other intraspinal-extardural lesions like synovial cysts, Tarlov cysts and ganglion cysts. Chiba et al have reported the largest series with eight patients and used the term discal cysts to describe this entity. The average ages of the patients reported by Chiba et al was 31.9 years (range 19-46 years) and were all males. The patient described in this report was a 13-year-old girl, which to the best of our knowledge is the youngest to be reported.

The specific clinico-radiological features of discal cysts are:

1. Clinical symptoms mimic those in patients with typical disc herniation.

2. Incidence at a slightly younger age at an upper intervertebral level.

3. A round to oval lesion with a low T1 and a high T2 signal intensity on the MRI.

4. Minimal degeneration of involved disc on discography / CT discography or MRI.

5. Connection between the cyst and the corresponding intervertebral disc on discograms with reproduction of severe pain in affected leg during injection.

6. Satisfactory clinical results after surgical excision of the cyst.

7. Cyst wall consisting of dense fibrous connective tissue.

8. Absence of disc material or a specific lining cell layer on HP Examination.

The etiopathogenesis of disc cysts proposed are

1. Resorbed epidural haematoma.

2. Focal degeneration and cystic softening of collagenous connective tissue of the disc with fluid production.

3. Injury to the cyst wall vasculature during discography.

The patient reported by us developed symptoms following an injury and the MRI was consistent with cystic degeneration in the intervertebral disc. Discography, CT discography and MRI are the investigation modalities of choice. MR imaging with sagittal T2 and enhanced T1 images is a non-invasive modality that can identify the communication between the cyst and the intervertebral disc. Intraoperatively, the cyst contained clear serous fluid and the disc space was devoid of disc material.MR images of our patient revealed a significant posterocentral disc protrusion at L5-S1 level. T1 hypo intensity and T2 hyperintensity within the protruded disc and the parent disc suggested the presence of fluid, which was confirmed during surgery. The cystic disc component was subligamentous with an intact outer annulus. The description of a disc cyst according to the literature reports is a fluid filled lesion outside the annulus and communicating with the parent disc through a rupture in the annulus. The patient discussed in this report had MRI features that were different from that of the classical disc cyst described in literature.  This may be the result of a posttraumatic cystic degeneration of the intervertebral disc with the formation of a fluid filled cystic cavity. Surgical decompression is advised only for those whose symptoms were unresponsive to non-operative treatment. Interlaminar fenestration and decompression of the cyst has been shown to provide a satisfactory outcome. Report of good results in patients treated by CT guided puncture and steroid injection is also available. Our patient had been symptomatic for 6 months before surgery and had a good outcome after interlaminar fenestration and cyst decompression.

Conclusion:

A fluid filled cyst confined within the annulus and directly extending from the parent disc, which had undergone cystic degeneration to be replaced by fluid, is a variant of the disc cyst described in literature. Disc cysts occur at a younger age and may be preceded by an injury. To the best of our knowledge this is the youngest patient reported with an intervertebral disc cyst. The clinical features closely resemble that of a herniated intervertebral disc and can be differentiated by the characteristic MRI features. Surgical decompression gives good results.