Case 10

Discussion:

Pulmonary tuberculosis is caused by the bacteria Mycobacterium tuberculosis (M. tuberculosis). Radiographic screening for active TB in high-risk populations may demonstrate findings consistent with prior and/or current infection. A Ghon focus refers to the initial site of parenchymal involvement at the time of first infection; a Ranke complex is the combination of a Ghon focus and enlarged or calcified lymph nodes; and Simon foci are apical nodules that are often calcified and result from hematogenous seeding at the time of initial infection.

On a single screening chest radiograph, detection of any abnormality—parenchymal, nodal, or pleural—with or without associated calcification, should result in an interpretation of indeterminate disease activity. Radiographic differentiation between active and inactive disease can only be reliably made on the basis of temporal evolution. Lack of radiographic change over a 4- to 6-month interval generally indicates inactive disease.

Primary disease
Lymphadenopathy is the radiologic hallmark of primary TB. On contrast material–enhanced computed tomographic (CT) scans, mediastinal tuberculous lymphadenitis, particularly when nodal size exceeds 2 cm in diameter, may have a characteristic appearance consisting of central areas of low attenuation. Although the appearance is very suggestive, it is not pathognominic. Differential include: atypical mycobacterial infection; lymphoma; metastases, particularly from testicular carcinoma; and benign conditions such as Whipple and Crohn diseases.

Parenchymal opacities typically an area of homogeneous consolidation occur in association with and affect the same side as nodal enlargement in approximately two-thirds of pediatric cases of primary TB.

Pleural effusion is an uncommon manifestation of primary TB in infants and young children (<2 years of age) (32). The prevalence of effusion increases with age and is reported to be 6–11% in children (58,59) and 29–38% in adult

Postprimary disease
Parenchymal opacities situated in the apical and posterior segments of the upper lobes and the superior segment of the lower lobes, often associated with cavitation, are the characteristic radiographic manifestations of postprimary TB.

Parenchymal involvement occurs in more than one segment in the majority of cases. Cavitation in single or multiple sites is evident radiographically in 40%–45% of cases of postprimary TB (66,78). Walls of cavities may range from thin and smooth to thick and nodular. Hilar and mediastinal lymphadenopathy are uncommon manifestations of postprimary TB and occur in only approximately 5% of cases. Tuberculous pleural effusion, although usually regarded as a manifestation of primary disease, may occur in association with postprimary disease in up to 19% of detected cases.

References:

• Pulmonary Tuberculosis: The Essentials. Ann N. Leung. Radiology. 1999;210:307-322.