What causes the Ghost Meniscus Sign in the knee on MRI?
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Answer:
The Ghost Meniscus Sign indicates a complete radial tear of the meniscus, a displaced meniscal root avulsion, or prior meniscectomy. The underlying pathological process involves complete disruption of the circular meniscal fibers, particularly at the meniscal root or through the body of the meniscus. When a complete radial tear transects the meniscus, the meniscal fragments become completely separated, creating an empty meniscal space. This sign is clinically significant because meniscal root tears compromise the meniscus’s ability to convert axial loads into circumferential hoop stresses, resulting in loss of meniscal function and increased joint contact pressures. The biomechanical consequences are comparable to total meniscectomy. Associated clinical findings include possible extrusion of the central third of the meniscus beyond the tibial margin and potential outward bowing of the medial collateral ligament. The posterior third and posterior horns are more commonly affected.
Why is it called so?
The sign is named “Ghost Meniscus” because the meniscus appears to disappear and reappear like a ghost on consecutive sagittal or coronal MRI slices. The ethereal, ephemeral quality of this appearance on sequential imaging inspired the nomenclature, accurately capturing the visual phenomenon observed during image interpretation.
Pathophysiology
The Ghost Meniscus Sign develops when the MRI slice plane passes exactly through the line of the meniscal tear or gap. At this precise anatomical level, the imaging plane intersects the disrupted meniscal fibers, producing complete or near-complete signal loss from the affected meniscus through partial volume averaging or complete absence of meniscal tissue in large defects. On consecutive slices, as the imaging plane moves away from the tear site, the meniscal signal reappears, creating the characteristic ghosting appearance. This phenomenon occurs because the meniscal fragments are widely separated and do not occupy the expected meniscal space at the level of the tear.
Alternative names: Empty Meniscus Sign, Zeichen des leeren Meniskus
Other associated named signs: Truncation Sign, Radial Linear Defect Sign, Dead Meniscus Sign, Meniscal Extrusion Sign
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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