Axial HRCT scan of the chest of a 30-year-old patient with primary ciliary dyskinesia (absence of outer and inner dynein arms) and advanced lung disease. Note significant involvement of the lung bases, with bronchial wall thickening, the signet ring sign, areas of consolidation, and attenuation differences. Source: Department of Clinical Pulmonology, Heart Institute, University of São Paulo School of Medicine - Hospital das Clínicas, São Paulo, Brazil, 2014.