A Disappearing Lung Mass: Round Pneumonia

To the Editor:

A 29-year-old woman presented with fever and cough for 2 days. She reported sudden onset of shortness of breath and right pleuritic chest pain. She had no history of recent travel, sick contacts, pets, environmental exposures, or smoking. She had no family history of lung cancer. She had a temperature of 36.2°C, pulse rate of 112 beats per minute, respiratory rate of 18 breaths per minute, and a blood pressure of 110/70 mm Hg. The physical examination was unremarkable except for the right-sided pleural friction rub. Laboratory data showed a white blood cell count of 26.1 × 10⁹/L with a left shift and unremarkable serum biochemistry. Human immunodeficiency virus screen, (1,3)-beta-D-glucan assay, urinary legionella, and streptococcal pneumonia antigen were negative. A chest radiograph (CXR) obtained on admission showed a round mass-like opacity in the right upper lobe (Figure, A ). All these findings were suggestive of infectious process, although malignancy could not be ruled out. The patient was started on broad-spectrum antibiotics. Chest computed tomography (CT) revealed a 5.6 × 4.9 × 5.6 cm round, pleural-based opacity with smooth margins in the right lung apex with normal pulmonary vasculature coursing through the mass (Figure, B & C). Although there was no mediastinal lymphadenopathy, possibility of malignancy was considered in the differentials, especially in the setting of large lung mass. CT-guided lung biopsy revealed benign lung tissue with acute inflammation. No organism was isolated from the sputum, urine, or blood. She was discharged on antibiotics on Day 4. After completion of 14 days of antibiotics, a follow-up CXR was performed, which revealed resolution of the lung mass (Figure, D) consistent with round pneumonia.

Figure.

(A) Chest X-ray at the presentation demonstrated round, pleural-based mass-like opacity in the right upper lobe (yellow arrow). (B, C) Same-day contrast-enhanced computed tomography of the chest revealed 5.6 × 4.9 × 5.6 cm round, pleural-based opacity with smooth margins in the right lung apex with normal pulmonary vasculature coursing through the mass. (D) Chest radiograph after completion of 14 days of antibiotic course revealed resolution of right upper lobe mass-like opacity consistent with round pneumonia.

Round pneumonia is rarely reported in adults, compared with children. Less than 1% of pneumonia in adults are round in shape, mimicking lung cancer.¹ Perhaps the true incidence in adults may be higher, as many cases get treated with antibiotics prior to imaging. In children, air bronchograms are usually present; however, in adults, air bronchograms are present in only 17%, delaying the diagnosis of pneumonia.² In a majority of pediatric cases, they occur in the superior segments of lower lobes; however, in adults they occur in upper lobes,² as seen in our case.

Pathogenesis behind formation of round pneumonia is unclear. Some argue that round pneumonia may represent an early stage of pneumonia when the infection is still contained, nonsegmental, and has smooth borders.¹ Others argue that the pores of Kohn and the canals of Lambert in the lungs, which allow intra-alveolar communication, may be blocked or poorly developed, resulting in compact and confluent consolidation.² In children, these communications are usually not well developed, resulting in higher prevalence of this pneumonia.² Several organisms have been reported in the literature; however, Streptococcus pneumoniae, Coxiella burnetii, and the Coronavirus are the most common etiological agents associated with round pneumonia in adults.

The importance of identifying round pneumonia in clinical practice lies in its close resemblance to lung cancer on imaging. Although clinical features like fever and cough can point toward infectious etiology, occasionally, bronchogenic carcinoma can present with pneumonia secondary to obstruction of bronchus with superimposed infection. Even F18-FDG positron emission tomography CT cannot differentiate round pneumonia from primary lung malignancy.³ This can lead to unnecessary invasive diagnostic biopsy, resulting in increased morbidity. A trial of antibiotics followed by a repeat CXR in 3-4 weeks should be considered in all adults presenting with solitary pulmonary mass, because round pneumonia can occur in patients of all ages.