📌 Not Every Bright Lesion Is a Synovial Cyst

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Although synovial cysts are cystic lesions, their MRI signal frequently deviates from a “simple cyst” pattern due to variable internal contents.

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MRI Signal Variations in Synovial Cysts — Mechanism-Based Explanation

1. Simple (Serous) Synovial Cyst

• T1WI: Low
• T2WI: High
• Low protein concentration
• Most favorable for percutaneous rupture

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2. High Protein Content / Viscous Synovial Fluid

• Chronic synovitis → increased protein concentration
• T1WI: Isointense to mildly hyperintense
• T2WI: Signal intensity is inversely proportional to protein content
• No hemorrhagic ancillary signs

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3. Hemorrhagic Synovial Cyst

• Caused by intracystic bleeding from vascular synovial lining
• Subacute stage (methemoglobin)
• Ancillary clues:
• Important because it can mimic a solid mass

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4. Vacuum Phenomenon (Gas-Containing Synovial Cyst)

• Nitrogen gas enters cyst from degenerated facet joint
• T1WI: Low signal (signal void)
• T2WI: Low signal
• GRE: Blooming artifact
• Never causes T1/T2 hyperintensity

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5. Calcified Synovial Cyst

• Long-standing degeneration and chronic inflammation
• T1WI: Low
• T2WI: Low
• Best detected on CT
• Often resistant to percutaneous rupture

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Take-Home Message

Synovial cysts are rarely “simple cysts.” Their MRI appearance reflects internal content—protein, blood, gas, or calcification—and must be interpreted in an anatomic and clinical context.

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#SynovialCyst #FacetJoint #SpinalStenosis

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