Sandbox:Aditya

Pathophysiology

The pathogenesis of lung abscess in primary lung abscess is mainly due to aspiration of oral pathogens at the time of altered level of consciousness in conditions such as alcoholism, Seizure disorder.Normally in a healthy individual, the defense mechanisms would cope up with the small amounts of aspirates with no ill effects, however, in conditions like alcoholism, DM, and immunocompromised state these defense mechanisms are compromised leading to decreased activity of alveolar macrophages and mobility of leucocytes.Alcohol also triggers vomiting center which in turn increases the risk of aspiration. Bronchial obstruction from benign or malignant intrabronchial lesions or extrinsic compression of bronchus as in middle lobe syndrome results in distal abscess formation are causes of secondary lung abscess It takes around 8-14 days to form a recognizable abscess after aspiration
The Basic pathology of lung abscess is destruction of segment or a portion of lobe, sometimes multiple lobes are involved based on severity of infection ( multiple abscesses ).after the bacterial invasion resulting in the inflammation of the lung tissue and release of various bacterial toxins,along with disrupture of fine blood vessel architecture and release of various proteolytic enzymes from the neutrophils leading to the formation of colliquative necrosis focus

Acute Lung abscess

• Gross morphology: Circumscribed with no so well defined borders with lung parenchyma fulfilled with necrotic debris
• Histopathology: central part of the abscess is filled necrotic tissue mixed with necrotic granulocytes and bacteria

Chronic Lung abscess

• Gross morphology: Irregular in shape with well-defined borders with lung parenchyma filled with grayish and thick detritus
• Histopathology: Abscess with pus with or without bacteria,a layer of pyogenic membrane is present around the abscess through which white blood cells migrate to form the fill the abscess cavitation.Lymphocytes, plasmacells and histiocytes surround the pygogenic membrane in a connective tissue

Location of abscess

• Right lung is most commonly involved than the left.
• 75% of the time the abscess presents on the posterior segment of the right apical lobe or apical segments of lower lobes of both the lungs
• Lateral part of posterior segment of upper lobe of right lung is most commonly involved in alcoholics

Classification

Based on duration

• Acute : If symptoms are present for less than 6 weeks before presenting to medical care.
• Chronic : If symptoms persist for more than 6 weeks

Based on Etiology

Primary: When Abscess develops among patients who were healthy previously or with high risk factors such as those prone for aspiration

• Aspiration of oropharyngeal secretions
• Immunodeficiency conditions like HIV
• Necrotizing pneumonitis

Secondary : When abscess develops among patients with an underlying lung abnormality

• Bronchial obstruction
• Hematogenic dissemination
• Infection spread from mediastinum
• Coexisting Lung Diseases

Based on mode of spread

Bronchiogenic

• Aspiration of Oropharyngeal secretions
• Bronchial obstruction by Tumor
• Foreign body, Congenital Malformations and Enlarged LymphNodes

Hematogenic

• Infective endocarditis
• Abdominal Sepsis
• Septic Thromboembolism

Risk Factors

Common risk factors in the development of lung abscess are

Common Risk Factors

• Alcoholism
• Seizer disorder
• Artificial ventilation
• Coma
• Neuromuscular disorders with bulbar dysfunction
• Nocturnal Aspiration /Inability to cough
• Bronchial obstruction
• Gingivo-dental sepsis
• Diabetes Mellitus
• Immunosuppression

Less Common Risk factors

• Drug abuse
• Malnutrition
• Mental retardation
• Gastroesophageal reflux disease

Causes

Common causes

• Dental/peridental infections
• Paranasal sinuses
• Alcoholism
• Seuizre disorder
• Patients on artificial ventilation
• patients with tracheotomy tube
• Intubated patients
• Infective endocarditis
• Abdominal sepsis
• IV drug abuse
• Septic thromboembolism

Microbiology

About 90% of the lung abscess is caused by polymicrobial infection from the oral pathogens that got aspirated.Anaerobes being the predominant type followed by Streptococcus Pneumoniae especially serotype type 3. But recently Klebsiella Pneumoniae has been the most isolated pathogen of lung abscess.Staphylococcus Aureus is the most common pathogen responsible for lung abscess in Children.The following table elaborates the Most common etiological pathogens responsible for lung abscess

Polymicrobial                                                                                                                                     Bacterial                     Fungal       Parasites                                                                                                               Anerobic                   Aerobic         Histoplasma Blastomyces Coccidoides Aspergillus Cryptococcus       Entamoeba histolytica Paragominus Westermani                                                                                         Gram Negative       Gram Positive       Gram Positive       Gram Negative                                                     Bacteroides fragilis Fusobacterum capsulatum Fusobacterum necrophorum       Peptostreptococcus Microerophilic streptococci Actinomyces       Staphyloccocus areus(including MRSA) Streptococcous Pneumonia Streptococcus Pyogens Nocardia       Klebsiella pneumoniae Heamophillus influenza type B Pseudomonas aeurongiosa Escherichia coli Legionella Pneumophilia Acinetobacter spp

Cardiovascular	No underlying causes
Chemical/Poisoning	No underlying causes
Dental	Gingivo-dental sepsis ,Dental/peridental infections
Dermatologic	No underlying causes
Drug Side Effect	No underlying causes
Ear Nose Throat	Paranasal sinusitis
Endocrine	Diabetis Mellitus
Environmental	No underlying causes
Gastroenterologic	GERD,Gastro and esophageal surgeries,
Genetic	Cystic Fibrosis
Hematologic	No underlying causes
Iatrogenic	No underlying causes
Infectious Disease	Abdominal Sepsis,Infective endocarditis;HIV-AIDS
Musculoskeletal/Orthopedic	No underlying causes
Neurologic	Seizure disorder,Coma,altered level of consciousness
Nutritional/Metabolic	No underlying causes
Obstetric/Gynecologic	No underlying causes
Oncologic	Bronchiogenic carcinoma
Ophthalmologic	No underlying causes
Overdose/Toxicity	No underlying causes
Psychiatric	No underlying causes
Pulmonary	Bronchiectasis;Cystic fibrosis;Bullous emphysema;Bronchial obstruction by tumor, foreign body or enlarged lymph nodes;Congenital malformations (pulmonary sequestration, vasculitis, cystitis);Infected pulmonary infarcts;Pulmonary contusion;Broncho-oesophageal fistula.
Renal/Electrolyte	No underlying causes
Rheumatology/Immunology/Allergy	Immunosuppresents ,corticosteroid therapy
Sexual	No underlying causes
Trauma	No underlying causes
Urologic	No underlying causes
Miscellaneous	No underlying causes

Natural History ,Prognosis and Complications

Natural History

The symptoms of Lung Abscess usually develop in more in the Fourth decade of life, and start with symptoms such as fever,cough,pleuritic chest pain and putrid smell sputum with hemoptysis. The symptoms of Lung abscess typically develop 8-14 days after the initial exposure to the infection with pathogens . Without treatment, the patient will progress to chronic stage and develop symptoms of night sweats and weight loss, which may eventually lead to Death.

Prognosis

The prognosis of Lung abscess is good with appropriate antibiotic treatment with a high success rate. The outcome mostly depends on the other associated conditions underlying lung abscess.The mortality rate is around 75% in patients with immunocomprimised state or bronchial obstruction .The presence of following factors is associated with poor prognosis among patients with Lung abscess.

• Large size cavities
• Old age
• Necrotizing Pneumonia
• Prlonged symptoms
• Abscess due to Aerobic bacteria
• Bronchial obstruction due to tumors or foriegn body( secondary abscess)
• immunocomprised individuals

Complications

Complications that can develop as a result of Lung abscess are

• Pyeopneumothorax
• Pleural Empyema
• Fibrosis and calcification of lung tissue
• Mediastinal,Pleural and Cutaneous Fistulas
• Sepsis