Imaging of the pulmonary manifestations of systemic disease.

Lung involvement in systemic disease may be a manifestation of the underlying pathological process, may be a complication of the underlying disease or may be related to the treatment. Lung pathology is dominant in certain diseases, such as in Wegener’s granulomatosis, but may be only rarely present, for example in Henoch-Schönlein purpura. However, lung involvement has a profound eVect on prognosis and may be challenging to accurately diagnose. In some patients, bronchoalveolar lavage and tissue diagnosis with transbronchial or percutaneous biopsy is not possible, due to the poor clinical state of the patient. Imaging often plays a central part when lung involvement is suspected clinically and this role has increased with the advent of high resolution computed tomography (HRCT). The chest radiograph may provide diagnostic information and be useful in follow up but it is relatively insensitive. HRCT now has several established roles: (1) May be diagnostic and if not will often narrow the diVerential diagnosis. 2 This in turn may reduce the need for biopsy. The HRCT signs of interstitial lung disease, small airways disease and bronchiectasis are well established (see box 1). (2) May demonstrate pathology when the chest radiograph appears normal, in patients with respiratory symptoms or abnormal pulmonary function tests. This particularly applies to diseases in which the radiographic signs are subtle or obscured by overlying structures, for example obliterative bronchiolitis, bronchiectasis, early fibrosing alveolitis, and fine walled cystic structures, such as in lymphangioleiomyomatosis. (3) Assessment of disease activity. Several studies suggest that ground glass shadowing on HRCT in fibrosing alveolitis corresponds histologically to active alveolitis. This in turn predicts a better response to treatment and better prognosis. Although ground glass shadowing is non-specific, it often represents reversible pathology, such as infection, haemorrhage, or oedema. (4) Assessment of interval change and treatment response, by acquiring comparative scans on follow up. (5) Prognostic information. (6) Planning a biopsy: for example transbronchial biopsy in peribronchial disease or percutaneous in subpleural disease and in guiding the optimal site for open biopsy, by defining areas of active alveolitis and avoiding areas of established fibrosis. (7) Prospective HRCTstudies may help in understanding the natural history of lung involvement in systemic disease. Recently, several groups have published HRCT findings in several of the systemic diseases. This evidence based article reviews the radiological features of lung involvement, including the recent literature on HRCT Box 1: HRCT signs (adapted from Webb et al p 118, 207, 243)