1 © 2015 Journal of Clinical Imaging Science | Published by Wolters Kluwer - Medknow Back to Basics – ‘Must Know’ Classical Signs in Thoracic Radiology Athiyappan Kumaresh, Mitesh Kumar, Bhawna Dev, Rajani Gorantla, PM Venkata Sai, Vijayalakshmi Thanasekaraan Department of Radiology, Sri Ramachandra Medical College and Hospital, Chennai, Tamil Nadu, India ABSTRACT There are a few signs in radiology which are based on many common objects or patterns that we come across in our routine lives. The objective behind the association between such common objects and the corresponding pathologies is to make the reader understand and remember the disease process. These signs do not necessarily indicate a particular disease, but are usually suggestive of a group of similar pathologies which will facilitate in the narrowing down of the differential diagnosis. These signs can be seen in different imaging modalities like plain radiograph and computed tomography. In this essay, we describe 24 classical radiological signs used in chest imaging, which would be extremely helpful in routine clinical practice not only for radiologists but also for chest physicians and cardiothoracic surgeons. Key words: Chest, computed tomography, signs, thoracic radiography, X-ray INTRODUCTION Radiological signs are classical and distinctive abnormalities, characteristic of a disease or a group of similar pathologies which can be seen either on a plain radiograph or on a computed tomography (CT) scan. These signs are generally based upon and associated with common objects and patterns that we come across in our routine lives. The objective behind establishing such an association is to help the reader understand and memorize their appearance and characteristics. The familiarity and application of these signs can facilitate in narrowing down the diferential diagnosis and timely management of the disease. The knowledge of these signs is helpful to residents and practitioners across various streams like radiology, internal medicine, chest medicine, and cardiothoracic surgery. The aim of this essay is to serve as a ready reference guide in the feld of chest imaging. Air crescent sign Air crescent sign appears as a crescent of air surrounding a soft‑tissue mass in a pulmonary cavity and can be seen in both plain X‑ray and CT scan [Figure 1]. Though it is characteristic of invasive pulmonary aspergillosis, it can also be seen in cavitating neoplasms, lung abscesses, and infections. This sign is considered a good marker of immune activity as it is seen when the necrotic tissue gets invaded by leukocytes and replaced by air in invasive pulmonary Received : 18‑05‑2015 Accepted : 21‑07‑2015 Published : 31‑07‑2015 Address for correspondence: Dr. Athiyappan Kumaresh, Department of Radiology, Sri Ramachandra Medical College and Hospital, Chennai, Tamil Nadu, India. E‑mail: drkumaresha@gmail.com www.clinicalimagingscience.org For entire Editorial Board visit : www.clinicalimagingscience.org/editorialboard.asp Editor‑in‑Chief: Vikram S. Dogra, MD Department of Imaging Sciences, University of Rochester Medical Center, Rochester, USA OPEN ACCESS HTML format Journal of Clinical Imaging Science PICTORIAL ESSAY Access this article online Quick Response Code: Website: www.clinicalimagingscience.org DOI: 10.4103/2156-7514.161977 This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms. For reprints contact: reprints@medknow.com How to cite this article: Kumaresh A, Kumar M, Dev B, Gorantla R, Venkata Sai PM, Thanasekaraan V. Back to Basics ‑ 'Must Know' Classical Signs in Thoracic Radiology. J Clin Imaging Sci 2015;5:43. Available FREE in open access from: http://www.clinicalimagingscience.org/text. asp?2015/5/1/43/161977