Fact-sheet: Synovial cyst
Updated on 03/17/2016 at 8:26 AM
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Definition
A synovial cyst corresponds to a herniation of the synovium into the tissues surrounding a joint, resulting in the formation of the cyst.
It most often represents dilation of a known anatomic recess. The most classic example is the popliteal cyst.
The cyst communicates with the joint cavity through a more or less wide neck and contains synovial fluid that is normal or thickened, clear or xanthochromic.
The wall is fibrous, lined with synovial cells.
The intraspinal synovial cyst is a posterior capsulosynovial articular expansion into the spinal canal, classically associated with facet joint osteoarthritis and most often located at the L4-L5 level. It is a rare cause of radiculopathy.
CT
Posterior facet joint synovial cyst:
- Extradural mass in contact with an osteoarthritic facet joint.
- Content most often of fluid density: hypodense, sometimes hemorrhagic. Wall of low density --> low sensitivity of detection with CT.
MRI
Cyst wall T1 and T2 hypointense.
Enhancement varies according to the degree of synovial inflammation.
Fluid content T1 hypointense and T2 hyperintense.
Spontaneous T1 hyperintensity indicates hyperproteinaceous content or the presence of methemoglobin.
Calcifications may be present.