Clinical History
A 68-year-old
female patient was referred for a lumbar spine MRI examination with intense pain at lumbar region and coexistence of right sciatica, resistant to treatment.
Imaging Findings
MRI disclosed a clearly demarcated extradural spherical lesion, one cm in diameter close to the right intervertebral foramen at the L4-L5 level. The lesion exhibited low signal intensity on
T1-Weighted images (WI) (Figure 1a) with peripheral post gadolinium contrast uptake (Figure 2), while on T2-WI it showed a rim of low signal intensity (Figure 1b, Figure 3). The continuity of the
lesion with the facet articulation arose the possibility of a synovial cyst, compressing neighbouring right L5 root. There was considerable clinical improvement after cyst removal and decompression
of the spinal root.
Discussion
Facets synovial cysts (FSCs) are considered an extrusion of the synovium through a capsular defect from a degenerated or unstable facet joint. These cysts occur most often at the L4-L5 level which is
known to be the most mobile part of the lumbar spine. These space-occupying lesions may produce compression to a nerve root and subsequent sciatica resistant to conservative treatment. FSCs may be
left untreated if asymptomatic. Otherwise surgical excision is the treatment of choice. Alternatively intraarticular injection of steroids under imaging guidance may be curative. Currently, MR
imaging is the examination of choice for the diagnosis of FSCs and previously used imaging methods such as myelography, CT and CT myelography, facet arthrography and CT facet arthrography are almost
abandoned. Variable signal intensities for the lumbar FSCs’ contents on MRI have been reported in the literature. FSCs are usually hypointense on T1-WI; however they may present iso- or
slightly hyper-intensity related to high protein content or small amounts of paramagnetic breakdown products of haemorrhage within the cyst. Cyst content on T2-weighted images is most frequently
mildly hyperintense in comparison with the CSF; in most cases. FSCs may have similar appearance with ganglia on MRI, although in the latter communication with the intraarticular space is lacking.
Also synovial lining is evident in FSCs on histology, that is lacking in ganglia cases. However, preoperative distinction between these two entities is not mandatory, when surgical decompression is
required. Spontaneous resolution of FSCs may occur and cyst rupture has been served as an explanation. Specific location and MR imaging characteristics may facilitate correct diagnosis of FSCs that
should be differentiated from solid extradural spinal neoplasms.
Differential Diagnosis List
Lumbar Facet Synovial Cyst
Final Diagnosis
Lumbar Facet Synovial Cyst
