A 44-year-old male with low backache with left lower limb radiating pain, straight leg raising test positive at 40 degrees in the left leg. Rest of the neurological examinations normal.
MRI revealed a well defined spherical extra dural cystic lesion with low signal intensity on T1 and high signal intensity on T2 antero lateral to thecal sac at L4-5 level.
Imaging wise possibility of discal cyst was given compressing left traversing L5 nerve root in lateral recess.
Left partial hemilaminectomy at L4-5 revealed blue colored cyst compressing the left traversing L5 nerve root. The cyst contained serous fluid without blood. A connection between the cyst and the disc was identified, and the cyst was removed at the base of the connection by dissecting the annulus fibrosus.
Histopathological examination of the cyst revealed fibrous connective tissue with hemosiderin deposits without lining cell layers, no disc materials.
The patient's low back pain and radiating pain in the left leg improved remarkably immediately after surgery.
The discal cyst is a new clinical entity and it communicates with the intervertebral disc. More and more cases are now diagnosed with advent of MRI. Histologically, intraspinal cysts of the facet are referred to as synovial cysts. Although the difference between discal cysts and synovial cysts is based on the presence of lining cells. The clinical symptoms of patients with discal cysts are indistinguishable from those of patients with a typical disc herniation manifesting as a unilateral single nerve root lesion. MRI and discography are useful for obtaining a presumptive diagnosis of this disease.
MRI features of discal cysts are a ventrolateral extradural cyst attached to a lumbar disc with or without rim enhancement on contrast enhanced MRI, occasional extension in lateral recess. These MRI features are the key to differentiating between a discal cyst and lumbar disc herniation. Discography and CT discography provide a connection between the cyst and the corresponding disc, and it is possible to differentiate discal cysts from lumbar disc herniation and other intraspinal cysts. However, need of this differentiation is controversial because the line of management is same for both of them. Removal of the cyst leads to symptom improvement, regardless of its origin.
The pathogenesis of discal cysts is still unclear. Several pathogeneses, such as resorption of a preexisting herniation and hematoma associated with a disc prolapse, have been suggested. Kyo et al. reported a case of discal cyst with an annular defect of the corresponding disc. Jeong and Bendo argued that the underlying pathological mechanism of discal cysts is a subsequent change in a herniated disc material. Tokunaga et al. confirmed the presence of cartilaginous tissue in the cyst wall and thought that the discal cyst might have developed from the absorption process of an intervertebral disc herniation. Chiba et al. proposed that discal cysts arise first from an underlying intervertebral disc injury that causes an annulus fibrosis fissure in the posterior intervertebral disc. Hemorrhage from the epidural venous plexus with a rich blood flow then occurs in the space between the peridural membrane and the vertebral body.
Whatever the pathogenesis may be, a discal cyst is responsible for the development of the symptoms in patients. Most of the discal cysts have been treated surgically. Lee et al. reported a case of recurrence among nine patients of discal cysts who underwent surgery at one year follow-up after the operation. It is suggested that careful long-term follow-up is necessary after surgery.
In 2007, Chou et al. reported a case of spontaneous regression of a discal cyst, patient who was treated with a routine epidural injection and selective nerve root block, and the discal cyst regressed spontaneously after 5 months. However, it is unclear whether steroid injection contributed to the regression of a discal cyst. Nevertheless, it is important to consider that although steroids influence the regression of discal cysts, potential spontaneous regression may also occur in discal cysts.
Standard therapeutic guidelines for discal cysts have not been established because the natural history and the long-term prognosis of discal cysts treated by surgery or percutaneous CT-guided aspiration and steroid injection are still unknown.
Reference : Discal Cyst of the Lumbar Spine J Korean Neurosurg Soc. 2008 Oct; 44(4): 262–264. Jae Ha Hwang, M.D., In Sung Park, M.D.