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 followed by Streptococcus Pneumoniae especially serotype type 3. But recently Klebsiella Pneumoniae has been the most isolated pathogen of lung abscess, especially in alcoholics.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

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
• Prolonged symptoms
• Abscess due to Aerobic bacteria
• Bronchial obstruction due to tumors or foreign body( secondary abscess)
• immunocompromised individuals

Complications

Complications that can develop as a result of Lung abscess are

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

Diagnosis

History and symptoms

Initial presentation of Lung abscess may be similar to that of pneumonia which includes

• Cough (initially non-productive later becomes productive sometimes followed by hemoptysis)
• Fever with shivering
• Night sweats
• Pleuritic chest pain
• Dyspnea
• Weight Loss
• Anemia and Fatigue is more commonly seen in anaerobic infections

The disease follows a fulminant course of high fevers with rapid progression if it is by non- anaerobic organisms like Staph-aureus.Fungi,Nocardia and Mycobacterium sps have an indolent and gradual progressive course

Physical examination

Physical examination findings of Lung abscess largely depends on the other underlying conditions,and organisms involved and severity of the disease and other comorbidities

General appearnce

Patient appears to be having Fever with chills and appear cachectic

• Anaerobic infection:- low-grade fever
• Other infection:- high-grade fever

HEENT

Poor oral hygiene with gingivitis, dental erosions or poor dentition

LUNGS

• Decreased breathe sounds on the side of Lung abscess
• Dullness to percussion
• Bronchial breathe sounds on Auscultation
• Inspiratory Crackles

If it is associated with other conditions like empyema or effusion clinical signs like

• Contralateral shift of mediastinum
• Absent of breathe sounds over the effusion can be appreciated

Extremities

Digital clubbing is seen in chronic cases of lung abscess