Background: Cryptogenic organizing pneumonia is increasingly being recognized as a major cause of diffuse infiltrative lung disease. The differential diagnosis of non-infectious diseases that resemble pneumonia should include this entity. Understanding the radiologic features of this entity will help in defining the correct diagnosis, although lung biopsy is needed to provide histopathologic confirmation. Treatment with steroids achieves an excellent response.
Objectives: To present a variety of radiologic findings on high resolution computerized tomography in eight sequential patients with COP, together with clinical and pathologic correlation.
Methods: Sequential HRCT examinations of eight patients (four males) aged 53–80 years (mean 65.5 years) with pathologically proven COP were retrospectively analyzed by a consensus of two experienced chest radiologists for the existence and distribution of airspace consolidation, ground-glass opacities, nodular thickening along bronchovascular bundles, small (<1 cm) and large (>1 cm) nodules. The distribution of radiologic findings was classified as unilateral or bilateral, located in the upper, lower or middle lobe, and central or peripheral. Also recorded was the presence or absence of mediastinal lymphadenopathy and pleural effusion. Correlation with clinical symptoms was analyzed.
Results: All eight patients had bilateral airspace consolidations: in two cases consolidations were limited to central fields, in four they were peripheral, and in the remaining two cases they were both central and peripheral. Small nodules were noted in six cases and large nodules in three. Ground-glass opacities were found in four cases. All patients had enlarged lymph nodes (1–1.5 cm) in the mediastinum. Radiologic abnormalities resolved or improved after steroid treatment in all patients.
Conclusions: HRCT findings of bilateral multiple heterogenic lung infiltrates and nodules associated with mild mediastinal lymphadenopathy in a patient with non-specific clinical symptoms are suggestive of COP; in such cases, lung biopsy is indicated. Radiologic resolution of abnormalities correlates well with clinical improvement under adequate steroid treatment.
 COP = cryptogenic organizing pneumonia
 HRCT = high resolution computerized tomography