Clinical History
A 68-year-old female patient with pain at lumbar region and right sciatica was referred for a lumbar spine MRI examination.
Imaging Findings
Sagittal T1-WI shows high-signal-intensity ovoid extradural lesion posterolateral to thecal sac and adjacent to right L2-L3 facet joint (Fig. 1a). Sagittal T2-WI shows multilevel disk protrusions and herniation at L2-L3 level (Fig. 2b). A rounded ring-like intensity is shown on sagittal T2-WI and STIR sequences, probably due to late sub-acute haemorrhage (Fig. 2b, c). Axial T2-WI at level of L2-L3 facet joint shows signs of degenerative disease, associated with small ovoid cystic lesion compatible with lumbar facet haemorrhagic synovial cyst.
Axial, sagittal and coronal CT slices show small subtle rounded lesion of soft tissue density (Fig. 2).
In the control lumbar spine MRI study, performed 6 months later (Fig. 3d), the lesion shows reduction of its diameter. The isointensity on sagittal T1-WI (Fig. 3a) and hypointensity in T2-WI (Fig. 3b) and STIR (Fig. 3c) sequences is in keeping with probable chronic haemorrhagic lesion.
Discussion
Lumbar facet joint synovial cysts are extradural intraspinal lesions that arise from the facet joint synovium. [1] Facet joint synovial cysts tend to occur at the lumbar spine, where most of the biomechanical spinal motion takes place. Although uncommon, the incidence of detected lumbar facet synovial cysts (LFSC) has increased with the wider availability of MR imaging. [2] These cysts represent an important, albeit rare, cause of back pain and spinal stenosis. Symptoms are usually ipsilateral, however, larger cysts can also cause contralateral radicular symptoms. [1]
It is commonly believed that LFSC result as a consequence of repetitive microtrauma. A high frequency of associated degenerative spondylolisthesis is seen in these patients, while abnormal spinal motion and degenerative changes of the facet joint lead to rupture of the synovial membrane and mixoid degeneration. [1]
MRI is the diagnostic method of choice for synovial cysts, which may appear as well circumscribed, extradural ovoid lesions, adjacent to facet joints. [4]
T1-WI hyperintensity may be caused by T1 shortening from methaemoglobin or proteinaceous fluid. Haemorrhage into the LFSC may show evidence of subacute breakdown products of blood in MRI and is associated with acute onset symptoms. CT may be used as a complementary study to better characterize the cystic content, for example gas, calcification and osseous structure involvement. [2]
Progressive symptoms have been described with increasing cyst size. [1]
After contrast administration, peripheral rim enhancement is typically seen in synovial cysts. [2]
Due to the relatively small size of the communication between the synovial cyst and the facet joint, it usually is not seen on MRI. [5] The communication enables the filling and emptying of the cyst, which is dependent on the mechanical changes of the spine, those explaining the size variations of the cysts on follow-up studies. [1]
Regarding the differential diagnosis, schwannomas have signal intensity on T1-WI that is both higher than that of the non-haemorrhagic and lower than that of the haemorrhagic synovial cyst. [3]
Perineural cysts show association with the nerve roots and are separate from the facet joints. Migrated herniated disk fragments tend to be anterior to the ligamentum flavum and have lower signal intensity on T2-WI. Extradural arachnoid cysts are typically CSF-filled outpouchings that occur typically in thoracic spine. [1]
In patients unfit for surgery, facet joint injection with steroid and long-acting anaesthetic can provide temporary or prolonged relief. Although, the optimal treatment remains a matter of debate, surgery to relieve sciatica caused by an LFSC is effective in a high proportion of patients. [2]
Differential Diagnosis List
Lumbar facet hemorrhagic synovial cyst
Meningioma
Ganglion cysts
Conjoint nerve root
Sequestered disc prolapse
Cystic neurofibroma
Schwannoma
Final Diagnosis
Lumbar facet hemorrhagic synovial cyst
