Post-Treatment, Inactive Tuberculosis

Definition: Resolution of tuberculosis is seldom complete. The usual residual changes include walled-off, caseous necrosis, thin- or thick-walled cavities, emphysema, bronchiectasis, obliterative bronchiolitis, focal pleural and parenchymal scars, and focal calcifications.

Emphysema, bronchiectasis, bronchiolitis: This lung shows extensive involvement of the peripheral part of the upper lobe and lesser involvement of the superior segment of the lower lobe by emphysematous bullae and some fibrosis. Bronchovascular structures in the central part of the upper lobe are normal, but more peripherally, the arrow indicates an ectatic airway. Scattered throughout are small, white nodules (one is next to the dilated airway), which represent calcified, caseous material probably in former airways. Most of the central parenchyma in the upper lobe is mildly emphysematous compared to that in the lower lobe.

The emphysema, bronchiectasis, and presumed bronchiolar disease all contribute to airflow obstruction.

Localized, inactive disease--caseous nodules and apical scar: Sometimes a tuberculous pneumonia becomes completely walled off, and only caseous material remains. Here, an apical scar (top) is connected to a nodule of caseous necrosis (center) that is encapsulated. The caseous material is friable and white. There was no evidence of active disease in this patient, although dormant bacilli are undoubtedly present in the caseous material.

Caseous necrosis refers to necrosis that has a crumbly, white, cheesy appearance. The term should be restricted to the gross appearance in tuberculosis. Nevertheless, this appearance is not specific for tuberculosis and can occur in fungal diseases, sarcoidosis, Wegener's granulomatosis, and neoplasms. Histologically, the material should be described as necrotic, rather than caseous. Similarly, the term tubercle should be reserved for the granuloma of tuberculosis.

More residual changes: This slice of left lung has the anterior surface toward the right. Two thin-walled cavities are shown here. The larger apical cavity is bordered by subpleural fibrosis posteriorly. Also note several dilated, thin-walled, upper lobe airways, which represent bronchiectasis. Compare these bronchovascular bundles with those near the bottom of the picture, where airways and vessels are about the same size. The branching, "Y"-shaped fibrosis is scar around bronchovascular bundles.

Tuberculous cavities, as shown here, have poor clearance and predispose to infection with fungi of various types, especially aspergillus. Fungus balls may result.

 

Note that the segments most likely to be involved with postprimary tuberculosis (apical-posterior segment of the upper lobe and superior segment of the lower lobe on the left) are located in the upper half of the picture. The apical-posterior segment is primarily involved here. The anterior segment of the upper lobe is lower and better perfused, perhaps escaping disease for this reason.

Clinical summary Miliary diseaseDiscussion

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