A 71-year-old man with chronic back pain had acute pain exacerbation, followed in the next month by progressive weakness of the right thigh. Neurological examination revealed myelopathy with a sensory level at T11. Spinal MRI (fig 1) revealed a well demarcated oval shaped lesion contiguous with the right T11–T12 facet joint causing dislocation and compression of the spinal cord that showed a subtle hyperintensity on T2 weighted images (TR/TE 3500/120). The lesion was inhomogeneously hyperintense on T1 weighted images (TR/TE 975/12) and hypointense on T2 weighted images and did not enhance after intravenous contrast medium. This appearance was consistent with a haemorrhagic spinal synovial cyst which was surgically removed with histological confirmation of the diagnosis and complete clinical recovery.
The pathogenesis of spinal facet synovial cysts is not established but is assumed to result from a combination of microtraumas and degenerative changes.1 The cysts most commonly arise in the lumbar spine but can also occur in the cervical spine whereas their thoracic occurrence is very rare.2 Chronic inflammation and neovascularisation of the cyst walls explain the possible intracyst bleeding which is attributed to rupture of neoformed vessels, even in the absence of significant trauma. Intracyst bleeding can be massive or minor but repeated. Macrohaemorrhage produces a sudden increase in the size of the cyst with compression on the nearby structures, including the spinal cord, and acute exacerbation of clinical symptoms.3 In the case of microhaemorrhages, the compressive effect is usually moderate and can underlie a persistent subacute symptomatology.3 The MRI appearance of non-haemorrhagic spinal synovial cysts is rather non-specific with a low signal in T1 weighted images and high signal in T2 weighted images combined with a regular rim of peripheral contrast enhancement.4 Otherwise the MRI appearance of haemorrhagic spinal synovial cyst exhibiting hyperintensity on T1 weighted images and hypointensity on T2 weighted images reflecting the presence of haemoglobin byproducts is more characteristic5 and enables a differential diagnosis with other more common extramedullary lesions, including arachnoid cysts, perineural (Tarlov) cysts, neurinoma and meningioma.4