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Pulmonary Lymphoid Hyperplasia and Lymphoid Interstitial Pneumonia (Lymphocytic Interstitial Pneumonia) *


Pulmonary Lymphoid Hyperplasia (Follicular Bronchiolitis)

Etiology, Prevalence, and Epidemiology

Pulmonary lymphoid hyperplasia, also known as follicular bronchiolitis or hyperplasia of bronchus-associated lymphoid tissue, is a benign condition characterized histologically by the presence of polyclonal lymphoid aggregates along the bifurcation of the bronchioles and along the pulmonary lymphatics and is mainly differentiated from lymphocytic interstitial pneumonia (LIP) by its typical distribution limited mainly to the airways. It is seen most commonly in association with connective tissue disease, particularly rheumatoid arthritis; immunodeficiency, particularly acquired immune deficiency syndrome (AIDS) (usually in children); hypersensitivity disorders; and as a nonspecific response in patients with airway infection, airway obstruction, or bronchiectasis.

Clinical Presentation

Pulmonary lymphoid hyperplasia may occur in children and adults (age range, 1.5–77 years). The most common presenting symptoms are progressive shortness of breath and cough. Other manifestations include fever, recurrent pneumonia, and weight loss.

Pathology

Pulmonary lymphoid hyperplasia is characterized histologically by the presence of discrete foci of hyperplastic lymphoid tissue, often associated with germinal centers, along the bronchovascular bundles ( Figs. 23.1 and 23.2 ). Hyperplastic lymphoid tissue also may be present within interlobular septa and visceral pleura.

Fig. 23.1, Pulmonary lymphoid hyperplasia in a patient with rheumatoid arthritis: pathologic findings. Low-power view shows hyperplastic lymphoid follicles (arrows) along the bronchovascular bundles.

Fig. 23.2, Pulmonary lymphoid hyperplasia: pathologic findings. Histologic specimen shows extensive lymphoid hyperplasia with lymphoid nodules, including lymphoid follicles, adjacent to small airways.

Manifestations of the Disease

Radiography

The chest radiograph may be normal or show bilateral reticular or reticulonodular opacities ( Fig. 23.3 ).

Fig. 23.3, Pulmonary lymphoid hyperplasia in rheumatoid arthritis. (A) View of the right lung from posteroanterior chest radiograph shows ill-defined nodular opacities. A similar pattern was present in the left lung. (B) High-resolution CT scan targeted to the right lung shows sharply defined peribronchovascular nodular opacities (arrows) in the right upper lobe.

Computed Tomography

The main high-resolution computed tomography (CT) findings consist of bilateral centrilobular and peribronchial nodules. Most nodules measure less than 3 mm in diameter. Nodules 3 to 12 mm in diameter are present in approximately 50% of patients, and patchy ground-glass opacities are present in approximately 75% of patients; small foci of consolidation may be seen in some patients (see Fig. 23.3 ). The nodules may be diffuse or involve mainly the lower lung zones. The nodules reflect the predominant histologic findings of peribronchiolar inflammation and coalescent germinal centers. Less common manifestations include mild interlobular septal thickening and bronchial dilation.

Differential Diagnosis

Centrilobular nodules are seen in a variety of diseases that affect predominantly the bronchioles or peribronchiolar interstitium. Common causes include hypersensitivity pneumonitis, respiratory bronchiolitis, and infectious bronchiolitis. Pulmonary lymphoid hyperplasia requires lung biopsy for definitive diagnosis.

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