• Aaron R Casha, Alexander Manché, Ruben Gatt, Wiktor Wolak, Krzysztof Dudek, Marilyn Gauci, Pierre Schembri-Wismayer, Marie-Therese Camilleri-Podesta, and Joseph N Grima.
• Department of Cardiac Services, Mater Dei Hospital, Msida, Malta Faculty of Medicine, Department of Anatomy, University of Malta, Msida, Malta aaron.casha@um.edu.mt.
• Eur J Cardiothorac Surg. 2014 Jun 1; 45 (6): 1011-6.

ObjectivesPrimary spontaneous pneumothorax has long been explained as being without apparent cause. This paper deals with the effect of chest wall shape and explains how this may lead to the pathogenesis of primary spontaneous pneumothorax.MethodsRib cage measurements were taken from chest radiographs in 12 male pneumothorax patients and 12 age-matched controls. Another group of 15 consecutive male thoracic computerised tomography (CT) were investigated using paramedian coronal and sagittal CT reconstructions to assess apical lung shape. A finite element analysis (FEA) model of a lung apex was constructed, including indentations for the first rib guided by CT scan data, to assess pleural stress. This model was tested using different anteroposterior diameter ratios, producing a range of thoracic indexes.ResultsThe pneumothorax patients had a taller chest (P = 0.03), wider transversely (P = 0.009) and flatter (P = 0.03) when compared with controls, resulting in a low thoracic index. Prominent rib indentations were found anteriorly and posteriorly on the lung surface, especially on the first rib on CT. FEA of the lung revealed significantly higher stress (×5-×10) in the apex than in the rest of the lung. This was accentuated (×4) in low thoracic index chests, resulting in 20-fold higher stress levels in their apex.ConclusionsThe FEA model demonstrates a 20-fold increase in pleural stress in the apex of chests with low thoracic index typical of spontaneous pneumothorax patients. Mild changes in thoracic index, as occurring in females or with aging, reduce pleural stress. Spontaneous pneumothorax occurring in young male adults may have a biomechanical cause.© The Author 2014. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.

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