Reason - Pathogenesis

Reason

Οι κυριότεροι αιτιολογικοί παράγοντες δημιουργίας πνευμονικού αποστήματος είναι οι εξής:

• πολυμικροβιακές λοιμώξεις που σχετίζονται με εισρόφηση:
  
  • συνήθως από αναερόβια μικρόβια
    
    • αναφέρονται στο 85-93% των περιπτώσεων
    • η είσοδος των μικροβίων προκαλείται συνήθως από διάσπαση του βλεννογόνου σε έδαφος ουλίτιδας
    • συνήθως απομονώνονται οι εξής μικροοργανισμοί:
      • Peptostreptococcus
      • Prevotella
      • Bacteroides
      • Fusobacterium
• λοιμώξεις από αερόβια μικρόβια (συνήθως μονομικροβιακές):
  
  • Streptococcus milleri (μπορεί να συμμετέχει και σε πολυμικροβιακή λοίμωξη)
  • group A Streptococcus
  • Staphylococcus aureus, συμπεριλαμβανομένου του μεθικιλλίνη ανθεκτικού στελέχους
  • S. aureus (MRSA)
  • Klebsiella pneumoniae
  • Escherichia coli
  • Pseudomonas aeruginosa
  • Mycobacteria, συμπεριλαμβανομένου του Mycobacterium tuberculosis
  • Nocardia, κυρίως σε ανοσοκατασταλμένους ασθενείς
  • Rhodococcus
• λιγότερο συνήθη αίτια:
  
  • παράσιτα
    
    • Entamoeba histolytica
    • Paragonimus westermani
  • μύκητες
    
    • Aspergillus
    • Blastomyces
    • Histoplasma
    • Cryptococcus
    • Zygomycosis

Pathogenesis

The most common way is a complication of pneumonia by aspiration:

• inoculation of microbes in the lung parenchyma by aspiration of large amounts of oral cavity fluids
• tissue necrosis occurs after 7-14 days and leads to the formation of the abscess
• in case the abscess communicates with the bronchial tree, purulent and smelly sputum is produced

Other ways of creating the lung abscess are:

• pulmonary embolism from septic emboli of the right heart chambers in the setting of infective endocarditis
  
  • usually multiple abscesses are formed
  • abscesses are formed in different (discontinuous) parts of the lung parenchyma
• haematogenous dissemination from purulent thrombophlebitis (e.g. Lemierre's syndrome)

Patient's personal history and clinical examination

Clinical picture

The clinical picture of pulmonary abscess due to anaerobic microbes includes the onset of subclinical symptoms, which may last for weeks, such as:

• cough, fever, purulent expectoration
• smelly sputum (indicating infection by anaerobic microbes) in 50% of cases
• in clinically confirmed pulmonary abscess from anaerobic microbes have been observed
  
  • average temperature 38.9^oC
  • average white blood cell count in peripheral blood 15000/mm³
  • average duration of symptoms to diagnosis about 14 days
  • weight loss in 43% of cases

The clinical picture may be lightning-like in cases of Staphylococcus aureus or Klebsiella pneumoniae infection with symptoms such as:

• high fever
• leukocytosis
• early extension of the abscess to other lobes or to the pleural cavity

Individual background

Main symptom

• cough, fever, purulent expectoration
• additional symptoms:
  
  • chest pain
  • haemoptysis
  • weight loss

History of present disease

Symptoms may be subacute or sluggish for weeks, and there may be a history of loss of consciousness or mental disorder.

Clinical examination

During the clinical examination, the following are found:

• fever
• poor oral hygiene and gingivitis
• cavernous or sandy breathing whispering
• absence of pharyngeal reflex
• keypad finger

Diagnosis

Diagnostic approach

The diagnosis of pulmonary abscess is typically achieved by performing a chest X-ray in patients with the above-mentioned clinical features:

• the chest X-ray shows a cavity with a hydraulic plane:
  
  • usually with a thick wall
  • there may be pulmonary infiltrates surrounding the cavity
• clinical findings supporting the diagnosis of aspiration lung abscess
  
  • subclinical symptoms
  • smelly sputum
  • risk factors for causing aspiration
• clinical picture with a lightning strike usually associated with a monomicrobial infection by Staphylococcus aureus or Klebsiella pneumoniae

Microbiological diagnosis requires isolation of the pathogenic microorganism from sputum or other material of the bronchial tree and has:

• little benefit-usefulness in isolating anaerobic micro-organisms that are usually contaminated by the normal flora of the oral cavity and respiratory tract
• high utility-usability in identifying pathogenic micro-organisms causing monomicrobial infections

Differential diagnosis

The differential diagnosis includes the following conditions:

• Inspiration
• septic pulmonary embolism from infectious right ventricular endocarditis
• neoplasms, including:
  
  • lung cancer
  • non-Hodgkin's lymphoma
  • metastatic carcinoma
• pulmonary embolism
  
  • necrotic pneumonia
    
    • tuberculosis
    • knockout
    • actinomycosis
    • Rhodococcus
    • Mycosis
      • invasive aspergillosis
      • blastomycosis
      • histoplasmosis
      • coccidiomyelitis
      • cryptococcosis
      • zygomycosis
    • parasitism
      • amoeba
      • paragonimiasis
      • echinococcosis
• vasculitis
  
  • granulomatous vasculitis
  • lung disease in rheumatoid arthritis territory
• emphysematous cyst
• stinky stunts

Diagnostic tests

Imaging tests

The imaging tests that are usually performed to diagnose pulmonary abscess are:

• chest X-ray
  
  • depicts a cavity with a hydraulic level:
    
    • usually with a thick wall
    • there may be pulmonary infiltrates surrounding the cavity
• chest CT scan
  
  • can be more revealing than a simple X-ray
    
    • the emergence of very small cavities
    • in the identification of neoplastic lesions
    • the distinction between abscess and fever

The American Thoracic Society (ATS) and the Infectious Diseases Society of America (IDSA) recommend that CT scans be performed in patients with pneumonia who do not respond to antimicrobial therapy, as CT scans:

• can distinguish pleural effusion from pulmonary thickening
• identify intraparenchymal abscesses, lymphadenopathy and solid lesions

In a published large series of patients diagnosed with pulmonary abscess the imaging findings were:

• unilateral lesions in 96.8% of cases
• simultaneous presence of pleural effusion in 9.5% of cases
• anatomical location of the abscess
  
  • posterior part of the upper lobe or apical part of the lower lobe in 85.3% of cases
  • basal parts of the lower lobe in 11.5%
  • in the medial lobe or glottis at 3.2%
• diameter of the abscess
  
  • <4cm at a rate of 15.9%
  • 4-8cm at a rate of 66%
  • >8cm at a rate of 18.3%

Transthoracic colour ultrasound can be useful in the differential diagnosis between pulmonary abscess and fever, where the demonstration of vascularisation in the thickening surrounding the abscess cavity confirms the presence of a peripheral pulmonary abscess with:

• 94% sensitivity
• 100% specialty
• 100% positive predictive value
• 94% negative predictive value