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Diagnostic imaging of lung abscess (Lung Abscess) and necrotizing pneumonia (Necrotizing pneumonia)

Lung abscess is defined as necrosis and cavitation of lung parenchyma secondary to microbial infection. Some authors use the term necrotizing pneumonia to distinguish pulmonary necrosis with multiple small abscesses from a larger cavernous lesion, although the two terms represent a continuum of the same process. .

Pulmonary Abscess (LUNG ABSCESS)

General Notes

– Cavitary lung lesions caused by infectious agents.

They may result from aspiration (most common) or pneumonia (pneumonia), or they may be secondary to bronchial obstruction, bronchiectasis, infective or infectious endocarditis spread the infection from elsewhere in the lungs.

Most abscesses are caused by anaerobes from the mouth in patients with pre-existing periodontal disease.

Alcoholics (most common), patients with seizure disorders that lead to aspiration, and patients with poor dentition are at higher risk.

– Anaerobic bacteria are the most common cause; Most lung abscesses are caused by a variety of microorganisms:

+ Peptostreptococcus

+ Bacteroides

+ Fusobacterium

– There are also:

Staphylococci (Staphylococcus)

Streptococcus (Streptococcus pyogenes)

+ Klebsiella

Haemophilus influenzae

+ Species Actinomyces

– Rarely:

+ Aspergillus

+ Cryptococcus

+ Histoplasma

+ Blastomyces

+ Coccidioides

+ Mycobacterium

Clinical signs:

It usually takes about 7-14 days from pneumonia to abscess formation, depending on the causative agent.

– Fever.

– A cough.

Foul-smelling phlegm

– Coughing up blood (Hemoptysis)

– Night sweats

– Anorexia and weight loss

Diagnostic imaging features:

  1. Conventional radiography

– Usually a nest (cavity)

– Caves usually have:

Thick wall (may become thinner as surrounding inflammation clears)

+ Smooth inner edge (Smooth)

+ Air-fluid level

– More common in the superior segments of the lower lobes or the posterior segments of the lower lobes.

Unlike pleural collections, lung abscesses usually have approximately the same length on both anteroposterior and lateral chest x-rays.

About one-third may have accompanying emphysema.

  1. Computer class cutting

Useful in distinguishing between lung abscess and emphysema.

– Round caverns with thick walls and air-fluid levels can be seen.

Lung abscess, located in the parenchyma, forms an acute angle with the chest wall.

Differential diagnosis

– Cavitary bronchogenic carcinoma

– Tuberculosis of the lung

– More cavitation points to necrotizing pneumonia rather than lung abscess

Many cavernous masses tend to be septic emboli.

Treatment

Antibiotics for 4-6 weeks or until chest X-ray shows the lesion is gone.

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– Percutaneous catheter drainage.

Surgery, either lobectomy or pneumonectomy, is available for patients who do not respond to medical treatment.

Symptoms

– Emphysema

Bronchopleural fistula (bronchopleural fistula)

– pleural fibrosis

Prognosis

With appropriate antibiotic treatment, more than 90% are cured.

Patients who are immunocompromised or with bronchial obstruction have a high mortality rate.

Figure 1. Lung abscess.

Axial contrast-enhanced chest CT image shows a large cavernous lesion in the left lower lobe with a relatively thick wall (black arrows). Cavities have smooth internal margins and air-fluid levels (white arrows). There is an inflammatory reaction around the lung (yellow arrow). Note the acute angle of the abscess formed with the posterior chest wall.

Figure 2. Lung abscess.

There is a thick walled cavern with smooth medial margin, located in the left lower lobe with air-fluid levels.

Figure 3. Lung abscess.

There is a thick walled cave with a smooth inner edge (red and white arrows). There is an internal air-fluid level (black arrow).

Figure 4. Lung abscess.

There is a thick walled cavern (white arrow) with smooth medial margin (red arrow), located in the right lung. Air-fluid levels are present (black arrows).

Necrotizing Pneumonia (NECROTIZING PNEUMONIA)

Necrotizing pneumonia refers to pneumonia that is characterized by the progression of necrosis in infected lung tissue.

Terminology

Although the term is sometimes used synonymously with cavitating pneumonia in the literature, not all necrotizing lung infections are complicated by cavitation.

Epidemiology

Necrosis can be seen in ~7% of patients with bacterial pneumonia. It can affect patients of all ages and is increasingly being reported in children.

Pathology

Progression to necrotizing pneumonia may occur due to virulence factors of the organism, factors of host susceptibility, or both.

It can be the result of a large number of pathogens, including:

– Staphylococci (Staphylococcus aureus)

Especially in young immunocompromised patients.

Klebsiella pneumoniae (Klebsiella pneumonia)

– Enterobacter spp.

– Nocardia spp. (pulmonary nocardia infection)

– Actinomyces spp. (thoracic actinomyces infection)

– Pseudomonas spp. (Pseudomonas aeruginosa pneumonia)

– Pneumococcus spp.: especially type III Pneumococcal sp.

Haemophilus influenzae (pulmonary Haemophilus influenzae infection)

Image features

Computer class cutting

If necrotizing infection is suspected and CT evaluation is required, it is preferable to have contrast-enhanced imaging because it allows for low attenuation and non-contrast assessment of the necrotic lung area.

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CT imaging may show clearly hypoattenuated areas with poorly contrast-enhanced parenchyma (representing liquefaction) in all or parts of the infected affected area (consolidation).

Normal lung parenchyma structure is often lost in the necrotic zone.

Treatment and prognosis

Treatment depends on the background agent while the prognosis depends on the severity of the pathogen as well as the susceptibility of the host. In general, complete recovery is predictable in children with necrotizing pneumococcal pneumonia, whereas in adults it is more difficult to predict.

Unlike an established lung abscess, interventional procedures (eg, drainage) may have poor outcomes in necrotizing pneumonia because of the potential for a bronchopleural fistula. In some centers, pneumonectomy is performed as a surgical option.

Differential diagnosis

For a large lesion with low internal density, consideration should be given to:

Pulmonary abscess: more defined with a few surrounding solidified lesions.

– Malignant lung disease with necrosis.

Figure 1. Mycoplasma necrotic pneumonia is difficult to treat causing pneumonia in children.

Chest computed tomography (CT) images of a 4-year-old male patient (a, b) and a 4-year 3-month-old female patient (c, d) hospitalized for necrotizing pneumonia (NP). Lung (a, c) and mediastinal (b, d) CT windows are shown at the same anatomical level. The CT features of necrotizing pneumonia include multiple air-filled caverns in the lung parenchyma.

Figure 2. Bedside chest radiograph of a 5-year-old female patient co-infected with 2009 pandemic virus (H1N1) and Streptococcus pneumoniae, showing multiple right-sided thin-walled air sacs (brackets), lesions opacification in the right middle lobe (black arrow) and indentation of the right diaphragm (white arrow).

Figure 3. (A) Axial computed tomography (CT) image showing necrosis of the right middle lobe with thin-walled air sacs (pneumatoceles) and three pleural sacs (one filled with air, one filled with air) translation and a mixture; arrows). (B) Coronal CT image shows large thin-walled air sacs and necrosis of the right middle lobe (brackets).

References

  1. Lung Abscess – Learningradiology
  2. Necrotizing pneumonia – Radiopaedia
  3. Severe necrotizing pneumonia in a child with pandemic (H1N1) influenza

BS. LE THI NY NY – Nguyen Tri Phuong Hospital

Works at anhvanyds

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