Pulmonary target sign
Citation, DOI & article data
The pulmonary target sign has been described in the lung parenchyma as a central high attenuation focus surrounded by one or more dense complete or incomplete ring-like consolidation, forming one or more circles. This sign has been predominantly reported on non-contrast chest CT in patients with COVID-19 pneumonia 1.
Synonyms used for this finding include the bulls-eye sign 10, target shape reverse halo sign 12,13 and rings of Saturn sign 14 but pulmonary target sign (or just target sign) has become the consensual term for this appearance.
For other uses of the term, see target sign (disambiguation).
A hypothesized pathophysiology of the target sign of COVID-19 on lung CT is that it is a manifestation of organizing pneumonia (OP) 7,8. It seems that the central nodule-like opacity may correspond to a bronchiole-vascular bundle which is occluded with exudates or clot, while the peripheral ring-shaped airspace opacities corresponds to pulmonary tissue filled with the fluid of infective air space opacity.
- the target sign usually includes the following radiologic characteristics 11:
- peripheral or subpleural location
- one or more dense surrounding rings
- surrounding rings could be complete or incomplete
- multiple lesions may occur
- close-by bronchovascular bundles may be involved
- usually adjacent ground-glass opacities
reverse halo sign with key differences
- focal central dense opacity rather than ground glass opacity
- no internal reticulation vs necrosis associated with the reverse halo sign 2
- atoll sign, however, the surrounding layer is thin 3
- rings of saturn sign14
- ring of fire sign,16 if central core was absent
- reverse halo sign with key differences
The pulmonary target sign usually coexists with other typical organizing pneumonia features including the halo or reverse halo sign, although the mechanism of its correlation with these features is not clear 9,10.
- 1. Müller CIS, Müller NL. Chest CT target sign in a couple with COVID-19 pneumonia. (2020) Radiologia brasileira. 53 (4): 252-254. doi:10.1590/0100-3984.2020.0089 - Pubmed
- 2. Marchiori E, Nobre LF, Hochhegger B, Zanetti G. CT characteristics of COVID-19: reversed halo sign or target sign?. (2020) Diagnostic and interventional radiology (Ankara, Turkey). doi:10.5152/dir.2020.20734 - Pubmed
- 3. Voloudaki AE, Bouros DE, Froudarakis ME, Datseris GE, Apostolaki EG, Gourtsoyiannis NC. Crescentic and ring-shaped opacities. CT features in two cases of bronchiolitis obliterans organizing pneumonia (BOOP). (1996) Acta radiologica (Stockholm, Sweden : 1987). 37 (6): 889-92. doi:10.1177/02841851960373P289 - Pubmed
- 4. Hoda A, Arash S. The Role of Chest CT Scan in Diagnosis of COVID-19. Advanced Journal of Emergency Medicine. 2020;4(2s).
- 5. Zhao, Li, Chen, Bo, Huang, Ya’nan, Yang, Minxia, Yang, Jianfeng, Zhao, Zhenhua. A Dynamic Follow-Up of Pneumonia Caused by Coronavirus Disease 2019 (COVID-19) on CT Scan. (2020) Iranian Journal of Radiology. doi:10.5812/iranjradiol.102847
- 6. Zhang FY, Qiao Y, Zhang H. CT imaging of the COVID-19. (2020) Journal of the Formosan Medical Association = Taiwan yi zhi. 119 (5): 990-992. doi:10.1016/j.jfma.2020.04.006 - Pubmed
- 7. Pogatchnik BP, Swenson KE, Sharifi H, Bedi H, Berry GJ, Guo HH. Radiology-pathology Correlation in Recovered COVID-19, Demonstrating Organizing Pneumonia. (2020) American journal of respiratory and critical care medicine. doi:10.1164/rccm.202004-1278IM - Pubmed
- 8. Saburi A, Schoepf UJ, Ulversoy KA, Jafari R, Eghbal F, Ghanei M. From Radiological Manifestations to Pulmonary Pathogenesis of COVID-19: A Bench to Bedside Review. (2020) Radiology research and practice. 2020: 8825761. doi:10.1155/2020/8825761 - Pubmed
- 9. Marchiori E, Silva JAM, Amorim VB , Zanetti G. Is the CT target sign specific to COVID-19 pneumonia?. J Bras Pneumol.46(6):e20200541.
- 10. McLaren TA, Gruden JF, Green DB. The bullseye sign: A variant of the reverse halo sign in COVID-19 pneumonia. (2020) Clinical imaging. 68: 191-196. doi:10.1016/j.clinimag.2020.07.024 - Pubmed
- 11. Jafari R, Maghsoudi H, Saburi A. A Unique Feature of COVID-19 Infection in Chest CT; "Pulmonary Target" Appearance. (2021) Academic radiology. 28 (1): 146-147. doi:10.1016/j.acra.2020.11.004 - Pubmed
- 12. Shaghaghi S, Daskareh M, Irannejad M, Shaghaghi M, Kamel IR. Target-shaped combined halo and reversed-halo sign, an atypical chest CT finding in COVID-19. (2021) Clinical imaging. 69: 72-74. doi:10.1016/j.clinimag.2020.06.038 - Pubmed
- 13. Lucas de Pádua Gomes de Farias, Fernando Henrique Caixeta Souza, Gustavo Borges da Silva Teles. The Target Sign and Its Variant in COVID-19 Pneumonia. (2020) Radiology: Cardiothoracic Imaging. doi:10.1148/ryct.2020200435
- 14. Jafari R, Colletti PM, Saburi A. "Rings of Saturn" appearance: a unique finding in a case of COVID-19 pneumonitis. (2021) Diagnostic and interventional radiology (Ankara, Turkey). doi:10.5152/dir.2020.20266 - Pubmed
- 15. Saburi A, Colletti PM, Jafari R. Pulmonary Target Sign: A New Finding or a Neglected Feature?. (2021) Academic radiology. doi:10.1016/j.acra.2020.12.024 - Pubmed
- 16.: Piyavisetpat N,Pongpirul K, Sukkasem W,et al.‘Ring of fire’ appearance in COVID-19 pneumonia. BMJ Case Rep 2020;13:e236167.doi:10.1136/bcr-2020-236167