Chest Film Clinic: What caused a solitary pulmonary mass in this patient with fever?

A 45-year-old man presented to the emergency department (ED) with fever and left-sided pleuritic chest pain. He had been in good health until 4 days earlier, when diffuse myalgias, weakness, and frontal headache developed. Two days later, these symptoms were accompanied by onset of fever (temperature, 39.4°C [103°F]) and left-sided pleuritic chest pain. He denied chills, rigors, shortness of breath, hemoptysis, and cough.

The patient denied any history of cigarette smoking but admitted to occasional binge alcohol consumption. His medical history was significant for epilepsy and an episode of pneumonia about 6 years earlier. Both of the patient's daughters had recently been ill with fever and diarrhea.

In the ED, a check of the patient's vital signs revealed a temperature of 38.6°C (101.6°F); blood pressure, 120/90 mm Hg; heart rate, 120 beats per minute; respiration rate, 18 breaths per minute; and oxygen saturation, 95% on room air. He was in no respiratory distress. Physical examination revealed faint crackles on auscultation of the left midlung region. There was no palpable lymphadenopathy or clubbing. The patient's white blood cell count was 19,700/ µL, with 84% neutrophils. His laboratory test results were otherwise unremarkable.

Posteroanterior (Figure 1) and lateral chest radiographs were obtained. Because of clinical suspicion of pulmonary embolism (PE), a CT pulmonary angiogram was also obtained (Figure 2).

Making the diagnosis

The patient's posteroanterior chest radiograph revealed a focal, round, 6-cm opacity (Figure 1, arrow) in the periphery of the lingula. There was no evidence of lymphadenopathy or pleural effusion. The CT image (lung window setting) demonstrated a confluent opacity, 6 cm in diameter, in the periphery of the lingula that contained an air bronchogram (Figure 2, arrow). There was no evidence of PE, lymphadenopathy, or endobronchial lesion.

Based on the imaging findings, clinical history, and laboratory data, a presumptive diagnosis of round pneumonia was made. The patient was treated with ceftriaxone intravenously and azithromycin orally for 2 days, followed by a 10-day course of oral levofloxacin. Follow-up chest radiographs several weeks after completion of antibiotic therapy were obtained to assess forresolution of the radiographic abnormality.

Discussion

Round pneumonia is a well-recognized entity in children. Although uncommon in adults, it is important to consider this diagnosis when an adult presents with a round pulmonary lesion and symptoms of pneumonia.

It has been hypothesized that round pneumonia is more common in children than in adults because of the relatively underdeveloped state of collateral ventilation in children, including the Kohn pores and channels of Lambert.¹ In addition, compared with adults, children have more closely apposed connective tissue septa and smaller alveoli. These factors combine to limit the spread ofinfection, thus producing a more compact, confluent area ofconsolidation, as opposed to the typical appearance of lobar consolidation in adults.¹

It has been estimated that fewer than 1% of cases of pneumonia in adults manifest as a round pulmonary lesion.¹ Because this is generally seen as a relatively early manifestation ofpneumonia, characteristic symptoms offever and cough may not always be present.² As the infection progresses, it spreads via direct intra-alveolar extension, as well as by centrifugal and peribronchial extension. This process results in progression to a more characteristic lobar consolidation. Although a round pulmonary opacity is usually seen in the early stage ofpulmonary infection, a similar appearance may also occasionally be seen during the resolution ofa lobar pneumonia.

The organisms responsible for round pneumonia are typically those that are associated with community-acquired lobar pneumonias--namely Streptococcus pneumoniae, Klebsiella pneumoniae, and Haemophilus influenzae. Additional causes include Legionella and fungal organisms. Other causes that are less commonly reported include Coxiella burnetti, Enterococcus cloacae, Mycobacterium tuberculosis, and severe acute respiratory syndrome-associated coronavirus.^3,4

Round pneumonia most often affects the lower lobes. The radiographic appearance varies and may range from a small, dense nodule to a large, ill-defined round opacity. The margins ofthe lesion are commonly smooth or mildly irregular, but they may also be spiculated or irregular.⁵ Air bronchograms are less commonly observed in round pneumonia than in a typical lobar pneumonia.

On CT scans, round pneumonia often appears as a heterogeneous, soft tissue attenuation mass, which may have associated air bronchograms, satellite lesions, spiculations, and pleural thickening.⁵ Several authors have noted that the most characteristic findings on CT scans include a broad-based lesion in contact with the pleural surface, with associated pleural thickening or satellite lesions.^5,6 It should be noted, however, that pleural thickening is generally seen only with peripherally located lesions.

Radiographic findings should promptly decrease after an appropriate course of antibiotics, with complete resolution expected within 4 weeks in most cases. Lesions that do not respond to antibiotics should be further evaluated to exclude malignancy.

Although the differential diagnosis for a solitary pulmonary mass is broad, the most important differential diagnostic considerations in this case were pulmonary infarction and lung cancer. Patients with pulmonary infarction may present with fever, pleuritic chest pain, and a focal peripheral pulmonary opacity. However, infarcts are typically more wedge-shaped than round.

Because of the presence of pleuritic chest pain and the absence of cough in this patient, a CT pulmonary angiogram was ordered to exclude the possibility of PE. In most cases, however, a presumptive diagnosis of round pneumonia can be entertained without the need to evaluate for PE.

Importantly, the bronchoalveolar form of lung cancer may present with a pulmonary mass that contains air bronchograms. This is the most common form to be identified in nonsmokers. Therefore, the absence of a smoking history in this patient does not exclude this diagnostic possibility. It is thus critical to obtain follow-up radiographs after antibiotic therapy to ensure resolution of presumed round pneumonias.

Persistence of a round pulmonary opacity with air bronchograms despite adequate antibiotic therapy should raise the concern for bronchoalveolar cell carcinoma. A chronic fungal infection should also be considered in this setting.

In conclusion, although relatively uncommon in adults, round pneumonia is an important diagnosis to consider when confronted with a patient who has a round pulmonary lesion and symptoms of infection.

The outcome in this case

The patient's symptoms resolved after antibiotic therapy. A follow-up chest radiograph obtained several weeks after antibiotic therapy showed complete resolution of the rounded opacity (Figure 3).

References:

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