Meniscus Sign in Radiology
The meniscus sign refers to a crescent-shaped radiographic finding that appears in different clinical contexts depending on the anatomical location being imaged.
Primary Manifestations
Pleural Effusion (Most Common Clinical Use)
The meniscus sign most commonly describes the characteristic curved interface of pleural fluid against the chest wall on radiographs 1. This represents the most clinically relevant and frequently encountered use of the term:
- Lateral chest radiograph: The meniscus becomes visible at approximately 50 ml of fluid
- Posteroanterior radiograph: The meniscus appears at approximately 200 ml of fluid
- Hemidiaphragm obscuration: Occurs at approximately 500 ml of fluid
The accuracy of using the meniscus sign to estimate pleural effusion volume is approximately 85-86% with excellent interobserver agreement (88-97%) 1.
Pulmonary Parenchymal Disease
In chest imaging, a pulmonary air meniscus sign describes a crescent-shaped air inclusion surrounded by consolidated lung tissue 2. The differential diagnosis includes:
- Aspergilloma (most common cause in non-endemic areas)
- Hydatid cyst (most common cause in endemic regions)
Vascular Imaging - Thrombus Morphology
In angiography, the clot meniscus sign refers to meniscoid or tram-track-like antegrade side-wall contrast opacification around a thrombus 3, 4. This finding has important prognostic implications:
- Associated with shorter procedure times (55 vs 85 minutes)
- Higher successful recanalization rates (89.3% vs 63.6%)
- Higher first-pass effect (32.1% vs 6.1%)
- Independent predictor of successful recanalization in basilar artery occlusion 4
Clinical Pitfalls
Do not confuse the meniscus sign with flow artifacts - the finding should be identifiable on multiple planes and consecutive slices to distinguish true pathology from technical artifacts 3.
When evaluating pulmonary embolism, the meniscus sign may be confused with the rim sign (contrast surrounding a central filling defect) or tram-track sign (parallel lines of contrast around an in-plane thrombus), which are distinct radiologic findings 3.