Fig. 3.3  Diffuse panbronchiolitis. (a) Scattered nodules are seen at a low power. The primary lesion is an in ammatory process of the respiratory bronchioles with marked associated foam cell accumulation. (Courtesy of Jeffrey L Myers, MD, Department of Pathology University

of Michigan). (b) In ammatory process in the respiratory bronchioles characterized by mononuclear cell in ammation in the wall. (c) Numerous foamy macrophages are present in the bronchiolar lumina (and adjacent alveoli)

Proliferative Bronchiolitis

Proliferative bronchiolitis is characterized by an organizing intraluminal exudate and is extensive and prominent in organizing pneumonia [13]. The intraluminal fbrotic buds (Masson bodies) are seen in the respiratory bronchioles, alveolar ducts, and alveoli. Proliferative bronchiolitis is most frequently associated with diffuse alveolar opacities on chest radiographs and CT scans [14]. A restrictive defect is found on pulmonary function testing.

Diagnosis

Patients who present with a chronic, insidious onset of cough and dyspnea, especially when the symptoms and signs do not follow a typical pattern, should raise the consideration of bronchiolitis.

Clinical Vignette

A 42-year-old female never smoker presented with a 12-week history of dyspnea with exertion and a nonproductive cough. She is a secondary school science teacher and an avid runner. She frst experienced a nonproductive cough with chest tightness about 15 weeks following accidental exposure to a sulfur-based chemical that overheated, giving off fumes. She has had progressive worsening of her dyspnea such that she is now not able to run. She has no chest pain, tightness, or heaviness. She is afebrile. Her respiratory rate is 16 breaths/min, and pulse oximetry shows 96% saturation on room air. Pulmonary examination shows slight expiratory wheezing and occasional bibasilar rhonchi that clear with coughing. Results of cardiac examination are normal, and no ankle edema is present. Lung function testing revealed moderate air ow obstruction

with moderate overdistension. The diffusing capacity was slightly reduced. A chest X-ray showed fndings suggestive of hyperin ation. Inspiratory HRCT demonstrated mild bronchiolar dilatation. Expiratory HRCT showed multifocal lobular air trapping in several lobes of her lungs. A surgical lung biopsy was performed and showed marked concentric narrowing of the bronchiolar lumen. Step sectioning of the tissue specimen confrmed the presence of complete obliteration of the bronchiolar lumen due to fbrosis (Fig. 3.4). Following treatment with bronchodilators and oral prednisone, her lung function stabilized with persistent reduction in her exercise capacity.

The differential diagnosis includes severe asthma, chronic obstructive pulmonary disease, hypersensitivity pneumonitis, and sarcoidosis. A multidisciplinary approach that considers the clinical setting and radiographic pattern is often helpful. When bronchiolitis is suspected, the most helpful tests are chest imaging, usually a high-resolution CT (HRCT) scan, and pulmonary function testing (see Box 3.1).

Fig. 3.4  (a) Slightly dilated bronchiole with minimal fbrosis (arrow) and a normal intervening lung (pentachrome stain; ×156 original magnifcation). (b) Severe concentric narrowing of the bronchiolar lumen

due to fbrosis (arrow) (pentachrome stain; ×156 original magnifcation). (Adapted from King [2])

Chest Imaging Studies

Chest radiography is of limited usefulness in the diagnosis and follow-up of patients with bronchiolitis and may be normal or may show varying combinations and degrees of any of the following: hyperin ation, peripheral attenuation of the vascular markings, and nodular or reticular opacities [15].

Inspiratory and expiratory CT scans are most useful in identifying fndings consistent with bronchiolitis (Fig. 3.5). Bronchiolitis is suggested on inspiratory CT scans by the presence of centrilobular thickening, bronchial wall thickening, bronchiolar dilatation, the tree-in-bud pattern, and the mosaic perfusion pattern [15–21].

Cylindrical bronchiectasis is frequently associated with bronchiolitis [18]. Expiratory CT scans are important in the assessment of air trapping, which is a characteristic fnding of partial airway obstruction [22]. Small peripheral centrilobular nodular parenchymal densities are nonspecifc indirect signs of small airway diseases [21].

These hazy nodular opacities appear as focal rounded areas of increased ground glass attenuation, measuring less than 1 cm in size [21]. The predominant CT fndings associated with proliferative bronchiolitis and organizing pneumonia are bilateral areas of consolidation. These are usually found in a predominantly peribronchial or subpleural distribution of the consolidation [20]. The fndings are asymmetric and vary over time.