69-year-old male patient presented with headache.
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Diagnosis: Synovial cyst
Synovial cysts typically have the imaging appearance of a simple cyst on MR imaging with hyperintense signal on T2-weighted images and without contrast enhancement. Internal hemorrhage may contribute to T1-shortening. They are associated with the facet joint, so location is key in narrowing the differential.
Synovial cysts are most commonly found in the lumbar spine in the 5th and 6th decade and demonstrate no clear gender predilection. They are only rarely reported in the cervical spine. When they do occur in the cervical spine, they are typically found at the C1-C2 facet joint or the lower cervical spine. The origin of synovial cysts is not well understood and is thought to either be sequelae of facet joint inflammation or trauma.
Cervical synovial cysts are usually asymptomatic. However, if large enough, mass effect may cause compression of the spinal cord or nerve roots. Specifically, sudden enlargement due to internal hemorrhage may result in acute symptomology. No management is necessary in cases of asymptomatic synovial cysts. Surgical excision is recommended in cases where symptoms are attributed to mass effect from the cyst, usually with respect to the spinal cord or the nerve roots.
The differential diagnosis of a cervical spine synovial cyst, especially one presenting at the level of C1-C2 includes an arachnoid cyst, epidermoid cyst, neurenteric cyst, and a meningioma. An arachnoid cyst will have MR imaging characteristics matching those of cerebral spinal fluid (CSF) on all sequences. Additionally, if a CT myelogram is performed, the arachnoid cyst will become opacified on delayed images. Epidermoid cysts are unique from other cysts in that they will restrict diffusion on MR imaging. Intradural cyst with varying heterogenous appearance depending on level of protein content. Neurenteric cysts tend to appear heterogenous on MR imaging and are usually seen in the setting of skeletal abnormalities and are thought to be due to abnormal duplication of the neurenteric canal. The key differentiation between a meningioma and a synovial cyst is that a meningioma will enhance homogenously, whereas a synovial cyst should not enhance at all.