Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at www.rsna.org/rsnarights. 723 PEDIATRIC IMAGING Jonathan฀R.฀Dillman,฀MD฀•฀Ramon฀Sanchez,฀MD฀•฀Maria฀F.฀Ladino- Torres,฀MD฀•฀Sai฀G.฀Yarram,฀MD฀•฀Peter฀J.฀Strouse,฀MD฀•฀Javier฀Lucaya,฀MD Unilateral hyperlucent hemithorax is a common pediatric chest radio- graphic finding that may also be seen at computed tomography. It may result from congenital or acquired conditions involving the pulmonary parenchyma, airway, pulmonary vasculature, pleural space, and chest wall, as well as from technical factors such as patient rotation. Unilateral hyperlucent hemithorax has a broad differential diagnosis that includes unilateral emphysematous or bullous disease, pneumatocele, foreign body aspiration, Swyer-James syndrome, congenital lobar emphysema, endobronchial mass, unilateral pulmonary agenesis, proximal interrup- tion of the pulmonary artery, scimitar syndrome, diaphragmatic hernia, and Poland syndrome. Although certain causes of unilateral hyperlucent hemithorax are clinically significant and potentially life threatening, oth- ers are of minimal or no clinical significance. When evaluating a patient with this finding, it is important to establish whether the apparent uni- lateral hyperlucent hemithorax is truly too lucent (hypoattenuating) or if the contralateral hemithorax is too opaque (hyperattenuating). It is imperative that radiologists be aware of the various causes of unilateral hyperlucent hemithorax so that they may diagnose the underlying con- dition and appropriately guide patient management. Introduction Unilateral hyperlucent hemithorax is a common pediatric chest radiographic finding that may also be observed at computed tomography (CT). The differential diagno- sis for this finding is quite broad, and it may result from a variety of congenital and acquired conditions. Certain causes of unilateral hyperlucent hemithorax may be life threatening, whereas others have little or no clinical significance. When evaluating a patient with this finding, it is important to establish whether the apparent unilateral hyperlucent hemithorax is truly too lucent (hypoattenuating) or if the contralateral hemithorax is too opaque (hyperattenuating). Expanding upon the Unilateral Hyperlucent Hemithorax in Children 1 CME FEATURE See฀www.rsna .org/education /rg_cme.html LEARNING OBJECTIVES FOR TEST 3 After฀reading฀this฀ article฀and฀taking฀ the฀test,฀the฀reader฀ will฀be฀able฀to: ■ Discuss the condi- tions associated with a unilateral hyperlu- cent hemithorax in children at radiogra- phy and CT. ■ Describe a sys- tematic approach for evaluating a unilateral hyperlu- cent hemithorax in children. ■ Discuss the ra- diographic and CT findings of the different causes of unilateral hyperlu- cent hemithorax in children. Abbreviations: AP = anteroposterior, PA = posteroanterior RadioGraphics 2011;฀31:723–741฀•฀Published online฀10.1148/rg.313105132฀•฀Content Codes: 1 From the Department of Radiology, Section of Pediatric Radiology, C. S. Mott Children’s Hospital, University of Michigan Health System, 1500 E Medical Center Dr, Ann Arbor, Mich 48109 (J.R.D., R.S., M.F.L.T., P.J.S.); FWRadiology, Fort Wayne, Ind (S.G.Y.); and Department of Pediatric Radiology, Hospital Vall d’Hebron, Barcelona, Spain (J.L.). Recipient of a Certificate of Merit award for an education exhibit at the 2008 RSNA Annual Meeting. Received May 13, 2010; revision requested July 20 and received August 16; accepted September 13. For this CME activity, the authors, editors, and reviewers have no relevant relationships to disclose. Address correspondence to J.R.D. (e-mail: jonadill@med.umich.edu). © RSNA, 2011฀•฀radiographics.rsna.org