Lung Abscess – A Preventable Pulmonary Disorder

Localized suppurative lesion in the lung is called lung abscess. Tuberculous and cystic cavities, though secondarily infected by pyogenic organisms, are not usually included under this term.

Causes

1. Aspiration Pneumonia: Aspiration of gastric contents or materials from the upper respiratory tract occurs during coma, anaesthesia or deep sleep.

2. Other types of Pneumonias

3. Systemic pyemia

4. Secondary infection of pulmonary infarcts

5. Necrosis and infection of bronchogenic carcinoma

6. Spread of amoebic liver abscess and primary pulmonary amoebiasis

7. Bronchial obstruction leads to abscess formation distally.

Impairment of cough due to painful conditions in the chest or during postoperative period and conditions which impair ciliary function (heavy smoking or bronchitis) predispose to abscess formation. Right lower lobe is the commonest site for aspiration and suppuration. In this supine comatose patient, the axillary segment of the right upper lobe and apical segment of the right lower lobe being the most dependent parts suffer more frequently. Next in frequency are the corresponding segments on the left.

Pathology

Suppuration and necrosis of lung tissue constitute the basic pathological process. The abscess is lined by granulation tissue which limits the spread of infection. Common organisms are those derived from the upper respiratory tract and mouth. These include aerobic and anaerobic streptococci, staphylococci, pneumococci and spirochaetes. Less commonly E.Coli, Clostridia and B. Proteus may be present. When the abscess ruptures into a bronchus, pus is expectorated. The cavity contains pus and air. The wall is thick and ragged compared to tuberculous cavity or cyst. Chronic abscesses may be multiloculated. When the contents are discharged, healing occurs by fibrosis.

Clinical features

Early symptoms are those of pneumonia with fever, cough, rigor, malaise and pleuritic chest pain. Initially cough may be unproductive. Hemoptysis is not uncommon. When the abscess ruptures into a bronchus the cough becomes postural. The sputum is large in volume (300-500 ml/day), purulent, blood-stained and foul smelling systemic symptoms depend on the virulence of the organisms and general condition of the patient. In a moderately severe case the patient is febrile, toxic and dyspneic. Painful clubbing of the fingers and toes develops in a few weeks.

Physical examination may reveal the presence of consolidation due to the surrounding pneumonic process. Pleural rub may be heard. Once the abscess opens into a bronchus, the auscultatory signs of cavernous and coarse post-tussive crepitations are heard.

Laboratory findings

Neutrophil leukocytosis is present in most cases on allowing it to stand in a conical glass, the sputum settles into the typical three layers (froth above, serous portion in the middle and thick nummular particles below). The organisms can be identified by Gram-staining and culture.

X-ray chest reveals consolidation with clearance in its centre. A partially drained abscess is seen as a cavity containing fluid and is necessary to locate the abscess. Tomography gives further details of the abscess wall and its contents.

Diagnosis

It is arrived at by clinical examination and chest X-ray. The etiology can be determined by microbiological examination of the sputum. Bronchoscopy helps in visualizing the main bronchi, to exclude obstruction and new growths and also to aspirate sputum for further tests. It may also help in clearing up obstruction and allowing drainage.

Complications

Pulmonary

• Severe hemoptysis

• Extension to other parts of the lung and to the other side

• Pleurisy, empyema, and pyopneumothorax; and

• Local fibrosis and bronchiectasic changes

Extrapulmonary complications

Brain abscess may develop due to metastases of septic emboli from the lung which reaches the cerebral circulation through the vertebral system of the veins (Batson’s system). Other complications include pulmonary Osteoarthropathy, emaciation and Cachexia due to loss of large amounts of proteins (in the form of purulent sputum) and infection. If left untreated, Lung abscess proves fatal.

Differential diagnosis

Lung abscess has to be differentiated from bronchiectasis, bronchogenic carcinoma, pulmonary tuberculosis, fungal infections, pulmonary cysts, and secondary neoplasms. Bronchiectasis is more chronic and usually bilateral. A cavitating bronchogenic carcinoma may resemble an abscess clinically and radiologically. Carcinoma is more common in smokers. The sputum is seldom profuse or purulent. It is more often blood stained with necrotic tissue being expectorated at times. Presence of hilar lymphadenopathy is suggestive of carcinoma. In cavitary pulmonary tuberculosis, the sputum is mucoid and often not foul smelling. Digital clubbing is less common. Tuberculosis affects the upper lobes more often, whereas abscess usually occupies the lower lobes. X-ray reveals thin-walled cavities, without free fluid level.

In endemic areas, lung abscesses should be investigated for fungal pathogens by sputum tests and immunological studies. Cystic disease of the lung is often bilateral and present from early life. Radiologically, the cysts appear thin walled. Rarely cysts may be solitary. Digital clubbing is less marked in cystic disease of the lung.

Treatment

Principles of therapy include antimicrobial drugs, drainage of the abscess cavity and surgery in intractable cases.

Antibiotics

Properly collected sputum uncontaminated by oropharyngeal microbes should be sent for culture and sensitivity studies and the antibacterial drug should be given in appropriate dosage till radiological clearance is complete. In most of the cases recovery is full in 4-6 weeks. Anaerobic infection has to be treated with metronidazole 500mg, given intravenously every 8 hours. Drainage of the abscess is achieved by postural drainage and gentle tapotement over the chest. Respiratory physiotherapy to stimulate cough and help expectoration is instituted early. If clearance of the abscess is unsatisfactory, bronchoscopic aspiration may help. With proper medical treatment, majority of lung abscesses heal.

Surgery

It is indicated in some circumstances such as failure of medical treatment, residual fibrosis with bronchiectatic changes, suspicion of bronchogenic carcinoma, severe hemoptysis and pleural suppuration. If the condition does not show improvement, after a reasonable course of medical treatment, surgery should not be indefinitely delayed. Necessary surgery should be performed before the general condition deteriorates.

Prevention of Lung Abscesses

Lung abscess is largely a preventable disease which can be forestalled by preventing aspiration pneumonia. Other measures include prompt removal of bronchial obstruction, complete treatment of pneumonia, and early diagnosis of pulmonary suppuration.