Infectious pneumonia in the immunocompetent host: What the radiologist should know

Abstract

Lung infections are an important cause of morbidity and mortality, particularly because of the rising antimicrobial resistance. According to the clinical setting, they can be categorized as community-acquired pneumonia and hospital-acquired pneumonia. Radiological patterns of lung infections are lobar consolidation, bronchopneumonia, interstitial pattern, and nodular pattern. In addition, typical imaging features of several infections serve as "red flag signs" in reaching a diagnosis or altering the management. It would be prudent for the radiologist to be well informed regarding these aspects of lung infections to be able to make a valuable contribution to the management.

Keywords: Imaging; immunocompetent; lung infections; pneumonia; radiological signs.

Figure 1

Coronal lung window image shows lobar pattern of consolidation in the right lower lobe. The upper margin of the consolidation is limited by oblique fissure. Air bronchogram is present

Figure 2

Bilateral upper lobe consolidation with extensive necrosis and areas of cavitation. Blood culture in this patient was positive for S aureus

Figure 3

Lobar consolidation in right lower lobe due to aspiration. Air bronchogram is absent. Centrilobular nodules are seen in dependent location in left lower lobe also

Figure 4 (A-C)

Right lobe Staphylococcal pneumonia. (A) lentiform fluid collection in right pleural cavity with thickening and enhancement of visceral and parietal pleura (split pleura sign) suggestive of empyema. (B) Cavity with air-fluid level in apical segment of right lower lobe. Bronchi are seen to end at the margin of the cavity (arrow) rather than being splayed, indicating intraparenchymal abscess. (C) Pneumatocele seen as a thin-walled air filled cyst

Figure 5

A 7-year-old child with 15 days history of cough, cold, and flu-like symptoms with rapid clinical deterioration requiring hospitalization. Large area of liquefied necrotic consolidation with cavitation in right lower lobe. PVL positive S. aureus should be considered in such patients

Figure 6

Chest radiograph showing extensive and coalescent larger acinar opacities in bronchopneumonia

Figure 7 (A and B)

A 40-year-old patient with acute onset of fever with dyspnea, not resolving with antibiotics. (A) Interstitial pneumonia in the form of well-defined consolidation, ill-defined scattered acinar infiltrates with air bronchograms (asterisk), GGO, and diffuse micronodular pattern. (B) Adenopathy (open arrow) seen on mediastinal window. There were microabscesses in the liver and spleen and ascites. The serology was positive for scrub typhus. Significant reduction in the lung lesions was seen after tetracycline therapy

Figure 8

A 40-year-old patient with fever, dry cough, headache, and dyspnea. Bilateral consolidation and GGO with subpleural and peribronchovascular predominance is seen. Throat swab was positive for H1N1

Figure 9

Chest radiograph in an infant with fever and respiratory distress shows features of bronchiolitis as hyperinflated lung fields and fine linear opacities due to atelectasis

Figure 10

A 12-year-old child with septicemia. Multiple well-defined nodules, more in subpleural region and most of them show a “feeding vessel sign” (arrow), suggesting septic emboli. Cavitation is seen in many nodules

Figure 11

Supine and prone axial CT scans showing “air crescent” sign of a dependent fungal ball in old lung cavity

Figure 12

Coronal reconstructed CT image showing fluid filled branching bronchoceles or “gloved finger sign” in ABPA

Figure 13

Serpentine old calcified guinea worm in muscles of the chest wall in a 60-year-old female overlying the right lung shadow

Figure 14

Bilateral dependent consolidation with air bronchogram. There is an anteroposterior gradient from normal lung to GGO to consolidation suggesting ARDS in the appropriate clinical setting

Figure 15

Wedge-shaped subpleural GGO in both lung apices. CT pulmonary angiogram in the revealed right pulmonary artery thrombosis

Figure 16

“CT angiogram sign.” Lobar consolidation with homogenous low attenuation and visibility of pulmonary vasculature through it

Figure 17

A 50-year-old male patient with dry cough for 6 months. Patchy wedge-shaped GGO which tend to be subpleural in location. The S. IgE levels in this patient were markedly raised upto 1818 kU/L, suggestive of chronic eosinophilic pneumonia

Figure 18 (A and B)

A 40-year-old male patient with cough and hemoptysis. (A, B) Combination of peripheral wedge-shaped GGO, consolidation, and cavity in left upper lobe (arrow), indicating a pulmonary vasculitis. ANCA was positive suggestive of granulomatous polyangitis

Figure 19 (A and B)

A 5-year-old male child with recurrent right lower lobe pneumonia and episode of massive hemoptysis. (A) Mass-like consolidation with cavitation in right lower lobe, with caudal extension into the retroperitoneum. (B) CT angiography shows an arterial feeder from the celiac artery (arrow). Radionuclide examination was positive for ectopic gastric mucosa indicating an infected transdiaphragmatic duplication cyst

Figure 20 (A and B)

(A, B) Imaging algorithm for approach to differential diagnosis of infectious pneumonia in immunocompetent host