signet / cabochon ring sign

Q: The presence of Signet or Cabochon ring sign on CT chest is mainly associated with which lung disease?

Answer: Bronchiectasis

Bronchiectasis can be diagnosed on CT chest by some of the hallmark signs such as:

1. their continuity with an airway

2. tendency to form clusters

3. formation of tramlines or honeycombing

4. signet  or Cabochon ring sign

Tramlines' appearance is due to dilated, thickened bronchial walls, and a signet or cabochon ring sign appears when the bronchus becomes larger than the corresponding vessel. In normal lungs, the vessel is larger than the corresponding bronchus.

Fig. A - Tramline sign - dilated, thickened bronchial walls (blue arrows)

Fig. B - Signet ring - The bronchi (red arrows) are larger than their corresponding arteries (white arrows)

#pulmonary

#radiology

References:

1. Ledda RE, Balbi M, Milone F, Ciuni A, Silva M, Sverzellati N, Milanese G. Imaging in non-cystic fibrosis bronchiectasis and current limitations. BJR Open. 2021 Jul 29;3(1):20210026. doi: 10.1259/bjro.20210026. PMID: 34381953; PMCID: PMC8328081.

2. Sawada H, Kudoh R, Yokoyama A, Hagiwara A, Hiramatsu K, Kadota JI, Komiya K. Chest X-Ray Features in 130 Patients with Bronchiectasis. Diseases. 2024 Dec 10;12(12):323. doi: 10.3390/diseases12120323. PMID: 39727653; PMCID: PMC11726920.

3. Bird K, Memon J. Bronchiectasis. 2023 May 22. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–. PMID: 28613561.