Sail sign
MSKRadiograph
At the elbow, an elevated anterior fat pad projects triangularly like a billowing sail; in the neonatal chest, the normal thymus casts a similar sail-shaped shadow.
What it means
At the elbow it indicates a joint effusion (often occult fracture); in the neonatal mediastinum it is the normal thymus.
Mechanism
At the elbow, joint distension displaces the anterior fat pad off the bone; in the chest the pliable thymus takes a triangular sail contour.
Associated conditions
- Radial head fracture
- Supracondylar fracture (children)
- Elbow joint effusion
- Normal neonatal thymus
Pearls
- An elevated anterior fat pad or any posterior fat pad implies an elbow effusion and likely fracture.
- The thymic sail sign is a normal finding in infants and should not be mistaken for pathology.
References
- Radiopaedia: Sail sign (elbow effusion; thymus)
For educational use only. This dictionary is a study aid and reference, not a diagnostic tool, and must not be used to guide clinical decisions or patient care. Imaging appearances vary; always correlate with the full clinical picture and confirm with a qualified radiologist.