Onion peel sign

Last revised by Liz Silverstone on 3 Sep 2024

The onion peel sign (also called the Cumbo sign or double arch sign) is pathognomonic for complete rupture of a pulmonary hydatid cyst. Gas enters both the pericyst and endocyst and gas-fluid levels may be present. The shrunken endocyst may mimic the appearance of onion peel.

History and etymology

It was first described by Cumbo in 1921 2.