Facet arthrography in an unusual presentation of a lumbar hemorrhagic synovial cyst.

An 84-year-old man experienced right buttock pain that radiated gradually to his right lower extremity over a few months before admission. MRI revealed a space occupying intraspinal lesion that was close to the right-sided L4-L5 facet joint and an extraspinal lesion posterior to the right-sided L5 lamina. The lesions appeared as hyperintense areas on T1 weighted images and heterogeneous areas on T2 weighted images. Facet arthrography under CT guidance revealed peripheral infiltration of the contrast medium only in the intraspinal lesion at early stages; subsequently, the contrast medium diffused into the extraspinal lesion, establishing a continuity of the right L4-L5 facet joint with both lesions, which were connected through the interlaminar space. A connection between the intraspinal and extraspinal lesions at the right-sided interlaminar space at the L4-L5 level was clearly noted during intraoperative examination. Histological examination revealed a hemorrhagic synovial cyst.