Reversed Halo Sign

The reversed halo sign, also known as the atoll sign, refers to a round area of ground-glass attenuation surrounded by a crescent (> 3/4 of a circle) or ring of airspace consolidation that is greater than 2 mm in thickness.

The reversed halo sign has been classically described in cryptogenic organizing pneumonia, but can be seen in a number of conditions. Recently it has been suggested that nodularity of the ring can be used to differentiate granulomatous infections and active sarcoidosis from cryptogenic organizing pneumonia, which has a smoother ring.

Differential considerations include:

• Cryptogenic organizing pneumonia (COP): Classical description of the reversed halo sign. Seen in up to 20% of patients with COP and thought to be fairly specific, although it can be seen in other conditions.
• Infections: Cryptococcosis, South American blastomycosis (paracoccidioidomycosis), schistosomiasis, pneumonococcal pneumonia, tuberculosis.
• Vasculitides: Wegener granulomatosis, dermatomyositis.
• Sarcoidosis:
• Lymphomatoid granulomatosis: Rare Epstein-Barr virus–associated lymphoproliferative disease, characterized by vascular destruction, classically in the lungs.

References

• Agarwal R, Aggarwal AN, Gupta D. Another cause of reverse halo sign: Wegener's granulomatosis. Br J Radiol. 2007 Oct;80(958):849-50.
• Algin O, Gokalp G, Topal U. Signs in chest imaging. Diagn Interv Radiol. 2010 Jul 28.
• Benamore RE, Weisbrod GL, Hwang DM, Bailey DJ, Pierre AF, Lazar NM, Maimon N. Reversed halo sign in lymphomatoid granulomatosis. Br J Radiol. 2007 Aug;80(956):e162-6.
• Gasparetto EL, Escuissato DL, Davaus T, de Cerqueira EM, Souza AS Jr, Marchiori E, Müller NL. Reversed halo sign in pulmonary paracoccidioidomycosis. AJR Am J Roentgenol. 2005 Jun;184(6):1932-4.
• Kim SJ, Lee KS, Ryu YH, Yoon YC, Choe KO, Kim TS, Sung KJ. Reversed halo sign on high-resolution CT of cryptogenic organizing pneumonia: diagnostic implications. AJR Am J Roentgenol. 2003 May;180(5):1251-4.
• Kumazoe H, Matsunaga K, Nagata N, Komori M, Wakamatsu K, Kajiki A, Nakazono T, Kudo S. "Reversed halo sign" of high-resolution computed tomography in pulmonary sarcoidosis. J Thorac Imaging. 2009 Feb;24(1):66-8.
• Marchiori E, Grando RD, Simões Dos Santos CE, Maffazzioli Santos Balzan L, Zanetti G, Mano CM, Gutierrez RS. Pulmonary tuberculosis associated with the reversed halo sign on high-resolution CT. Br J Radiol. 2010 Mar;83(987):e58-60.
• Marchiori E, Zanetti G, Hochhegger B, Irion KL. Re: Reversed halo sign: nodular wall as criterion for differentiation between cryptogenic organizing pneumonia and active granulomatous diseases. Clin Radiol. 2010 Sep;65(9):770-1.
• Tokuyasu H, Isowa N, Shimizu E, Yamadori I. Reversed halo sign associated with dermatomyositis. Intern Med. 2010;49(15):1677-8.
• Tzilas V, Bastas A, Provata A, Koti A, Tzouda V, Tsoukalas G. The "reversed halo" sign in pneumonococcal pneumonia: a review with a case report. Eur Rev Med Pharmacol Sci. 2010 May;14(5):481-6.
• 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). Acta Radiol. 1996 Nov;37(6):889-92.