Reversed halo sign
 Discussion of Reversed halo sign
- The reversed halo sign is defined as central ground-glass opacity surrounded by denser consolidation of crescentic (forming more than three fourths of a circle) or ring (forming a complete circle) shape of at least 2 mm in thickness.
- The reversed halo sign is a relatively specific sign for cryptogenic organizing pneumonia, although it is only seen in of fifth of patients with the disease.
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 References for Reversed halo sign
- Kim, Sang Jin, Lee, Kyung Soo, Ryu, Young Hoon, Yoon, Young Cheol, Choe, Kyu Ok, Kim, Tae Sung, Sung, Ki Jun. Reversed Halo Sign on High-Resolution CT of Cryptogenic Organizing Pneumonia: Diagnostic Implications. Am. J. Roentgenol. 2003 180: 1251-1254.