Bronchiolitis obliterans organizing pneumonia

Oct 29, 2000

Histologic features--Idiopathic bronchiolitis obliterans organizing pneumonia (BOOP), also known as cryptogenic organizing pneumonia (COP) in the United Kingdom, is a disease characterized by granulation tissue polyps within the lumina of bronchioles and alveolar ducts and patchy areas of organizing pneumonia.^{2, 60, 61} Fibrosis and inflammation are not conspicuous features of BOOP. BOOP may be idiopathic (cryptogenic organizing pneumonia), although a BOOP-like reaction may be seen with pulmonary infections, drug reactions, as a complication of organ transplantation, collagen vascular disease, Wegener's granulomatosis, and following toxic fume inhalations.^{1, 61}

Clinical findings--Patients with idiopathic BOOP typically present with a several month history of non-productive cough.^{1, 2} Most patients report symptoms being present for <6 months.⁶² Low grade fevers, malaise, and shortness of breath are also seen.² The presentation has been characterized as "flu-like" in 40% of patients. PFTs typically reveal a restrictive defect. The prognosis of idiopathic BOOP is good; patients usually respond to corticosteroids.²

Radiographic findings--Chest radiographs: The characteristic chest radiographic features of idiopathic BOOP include bilateral, patchy, nonsegmental areas of air space consolidation and/or ground glass opacities.¹⁰ A peripheral distribution is characteristic, although not seen in the majority of patients (14%) (figure 11 -- 31KB).¹⁰ Recurrent/migratory opacities, often in the upper lobe, have been reported. Small nodules may be present, most commonly accompanying air space consolidation. Irregular linear opacities are less common and generally are not dominant features on the radiograph. Pleural effusions are also uncommon. Adenopathy and honeycomb cysts are considered rare.^{10, 63}

CT and HRCT: CT and HRCT scans in BOOP may demonstrate:^{3, 63-66}

Patchy air space consolidation (80%) or ground glass opacity (60%), often with a subpleural (50% to 60%) and/or peribronchiolar distribution. No particular zonal predilection is present (figure 12 -- 44KB), (figure 13A -- 33KB), (figure 13B -- 40KB), (figure 13C -- 57KB), and (figure 13D -- 33KB);
small ill-defined nodules have been reported in 30% to 50% of cases, and may be peribronchiolar in distribution;
bronchial wall thickening and bronchial wall dilation have also been described; and
irregular, large nodules or masses.⁶⁷

Irregular linear opacities, pleural effusions, and adenopathy may variously be seen, but are generally less common. HRCT provides useful information for guiding surgical biopsy.^{3, 5, 10} Most patients respond well to treatment (figure 13A -- 33KB), (figure 13B -- 40KB), (figure 13C -- 57KB), and (figure 13D -- 33KB), although relapses do occur and a small minority of patients may even die due to respiratory failure.

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