Lobar Pneumonia

The classical "primary" lobar pneumonia of nonimmune tuberculosis may affect any part of the lung, usually a whole lobe but sometimes only a segment (Fig. 5.4). It is probably a little more common in the upper lobes, but no part of the lung escapes and being influenced by the site of the lobar infection is not a safe way to exclude tuberculosis. Clinically the patient may present at any age, with a high temperature and the physical findings of lobar pneumonia. Quite contrary to this acute presentation, in other patients the lobar consolidation may be seen on a chest radiograph when there is little or no clinical ill health and the pneumonia is quite unsuspected. There is no atelectasis in the early stages, nor is there a pleural effusion associated with the lobar pneumonia.

There may be M. tuberculosis in the sputum or gastric lavage, but failure to find the bacillus does not invalidate the diagnosis. A tuberculin skin test may be negative or change to positive during the illness, usually in 2-3 weeks after the onset.

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Fig. 5.4 A-F. Tuberculous primary lobar pneumonia can occur in any lobe or segment of lung. There is almost always hilar lymphadenopathy. A, B Primary pneumonia in the posterior segment of the right upper lobe, with right hilar lymphadenopathy. C, D Left upper lobe tuberculous pneumonia: the enlarged lymph nodes are only clearly seen in the lateral projection. There is also tuberculous infection in the lower thoracic spine. E Right lower lobar pneumonia. There is probably lymphadenopathy, partially obscured by the lung consolidation. F Bilateral primary pneumonia in the right middle lobe, the lingula, and the anterior segment of the right upper lobe. This child had had a mild but persistent cough and a low fever for 2 weeks. (A, B, E, F Courtesy of Semin Roentgenol, 1979).

The lobar consolidation is definite but seldom dense, yet it is more opaque than the hazy and ill-defined consolidation which is usually seen in a viral infection. The distinctive feature of primary pulmonary tuberculosis is enlargement of the hilar and mediastinal lymph nodes, which is nearly constant in primary tuberculosis at any age; in adults, this lymphadenopathy can be seen on standard posteroanterior (PA), high kV, grid films of the chest. In children it may be necessary to obtain a lateral view as well as the frontal film to reliably identify the enlarged nodes: as always, full inspiratory radiographs are essential. Lymphadenopathy is a way to distinguish tuberculosis from pyogenic pneumonia, in which hilar adenopathy recognizable on standard radiographs is distinctly unusual (although it may be visible with CT). "If the nodes are enlarged and can be seen on a standard radiograph in a case of lobar or segmental pneumonia, then suspect tuberculosis." This is a reliable dictum. It was the Viennese pathologist, Anton Ghon, who in 1912 first described the combination of a focal tuberculous lesion in the lung with regional lymphadenopathy. Radiologists have continued to recognize the Ghon complex as important evidence of a tuberculous infection.

Tuberculous consolidation resolves from the periphery towards the hilum, often with a well-defined edge (Fig. 5.5). When this occurs in a lung segment, such as the superior segment of the lower lobe, it may radiologically resemble a tumor, particularly if this is the appearance on the first chest radiograph (Fig. 5.6). In children this will be an unlikely diagnosis, and malignant disease of the lung (apart from metastases) is uncommon in many parts of the tropics at present.

Tuberculosis in one-third of babies may progress radiologically for as much as 3 months, even during intensive antibiotic therapy. In addition to extension of the lobar consolidation, there may also be increasing lymphadenopathy, thought to be the result of a high-sensitivity reaction during the first 2-10 weeks after infection. In most patients, the resolution of the radiographic changes of tuberculous pneumonia is slow: it often takes as long as 9 months even when adequate therapy has been given and when the clinical improvement has been dramatic (as is the case in many patients).

The considerable discrepancy between the x-ray appearance and the well-being of the patient may be useful confirmation of the diagnosis when there has been no other more positive proof of tuberculosis (see Figs. 5.5, 5.6). Any lobar pneumonia which disappears within 2 or 3 weeks, leaving a normal chest radiograph, is probably not tuberculous.

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Fig. 5.5 A-D. The resolution of primary tuberculous pneumonia usually occurs from the periphery inwards towards the hilum. A Right upper lobe pneumonia, moderate pyrexia and cough, and a negative PPD. The patient was given penicillin, after which there was some clinical improvement but persisting pyrexia (December). B By January the PPD had converted and the lobar pneumonia had begun to resolve from the periphery towards the hilum. There were tubercle bacilli in the sputum and antituberculous therapy was started. C By March consolidation had decreased further towards the hilum. D One year later, after continuous treatment, there is calcification in the small residual granuloma. The patient had remained clinically fit. This pattern of healing can be seen in a patient of any age. (Courtesy of Semin Roentgenol, 1979)

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Fig. 5.6. A-D. The resolution of primary (nonimmune) tuberculosis in a young male adult. A July: Persistent loss of weight and cough due to a tuberculous infection in the superior segment of the left lower lobe, with perihilar lymphadenopathy. PPD was positive and there were M. tuberculosis in the patient's sputum. Treatment was started with three drugs. B Four months later consolidation is less pronounced but the lymph nodes are still enlarged and appear much more dense. C After a further 3 months' treatment the consolidation and nodes are again much smaller: shrinkage has continued from the periphery inwards. If the patient had been radiographed at this stage, or at the stage depicted in B, the "mass" could have been mistaken for a neoplasm. D After another 14 months of treatment there has been much improvement, but the lymph nodes are still slightly enlarged.