Formation of single or multiple, thin- or thick-walled cavities on either side of the lung fields, especially in the apical or posterior segment and superior segment of the lower lobe, is considered an important hallmark of reactivation pulmonary tuberculosis. 1 Differential diagnosis of a cavitory lesion on chest x-ray includes infectious diseases like common bacterial infections (Staphylococcus, Klebsiella, anaerobes), necrotizing pneumonias and lung abscesses, septic pulmonary emboli, fungal infections, parasitic infections, and, most importantly, mycobacterial infections in a country like India where tuberculosis is rampant. However, noninfectious causes include malignancies (squamous cell carcinoma of the lung), rheumatologic diseases, pulmonary infarcts, and Wegener granulomatosis.2
How does “tennis racket” form?
Involvement of bronchus in the tuberculous process, causing its narrowing or occlusion with the dilatation of its distal part beyond this narrowing, due to the local wall destruction with weakening, appears as a ring shadow (tuberculous cavity) while the proximal part of the draining bronchus (toward hilum) is also either narrowed, thickened, or dilated by the tuberculous process, giving it the appearance of a “tennis racket” shadow. 3 Histological features of the wall of such a “cavity” are similar to those of the bronchial wall with or without tuberculosis foci in it.4
Clinical significance
The ring shadows or tubercular cavity has abundant significance in the definitive diagnosis of active tuberculosis infection as a solid nodule of 2 cm in diameter devoid of communication with the bronchi. The number of tubercle bacilli ranges from 102 to 104, while a cavitory lesion of the same size contains approximately 107 to 109 bacilli. Thus, cavitory disease having bronchial communication has a good association with a sputum smear positivity, as a large number of bacilli are excreted with the sputum and such patients are highly infectious.5 Therefore, the “tennis racket” sign can be considered one of the radiological hallmarks of active pulmonary tuberculosis.3
Learning points
No radiological pattern or sign is specific for tuberculosis; however, the presence of “tennis racket” sign endorses higher grades of bacteriological presence.
The presence of “tennis racket” sign on chest radiograph should ignite a search for underlying active pulmonary tuberculosis.
Figure 1.
(A) Chest x-ray PA shows a thick walled cavity in the left upper zone with a tubular shadow starting from it, extending up to the left hilum, forming a ‘tennis racket’ appearance. (B) Highlighting the ‘tennis racket’ sign.
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