On CT abdomen, the 'beak sign' is seen at the margins of a mass in the liver, indicating that it arises from the liver parenchyma. This sign describes:

• A Gas outlining the mass in a pattern resembling a beak
• B The sharp interface between a vascular lesion and the hepatic vein
• C Compression of the mass by the falciform ligament
• D The blending of the mass with adjacent hepatic parenchyma creating a beak-like projection of liver tissue ✓

Explanation

The 'beak sign' on CT refers to the tapering wedge (beak-like) of normal organ parenchyma at the edge of a mass, indicating that the mass is intrinsic to (arises from within) that organ rather than extrinsic. It is seen in liver, kidney, and spleen to confirm organ of origin. When a hepatic mass shows the beak sign, adjacent liver tissue wraps around its margins. This is contrasted with extrinsic compression, which causes displacement of the organ with a smooth interface. It is also described for renal masses (distinguishing intrarenal from retroperitoneal masses).

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.