Aetiological aspects of lung abscess.
Lung abscess is a lesion of the pulmonary parenchyma containing purulent material and caused by a variety of aetiological factors.
Lung abscess is never primary; it is almost always secondary to something else. The aetiological aspects of lung abscess have witnessed a phenomenal change in trend in the present century thanks to the advent of powerful chemotherapeutic agents, advances in skilled anaesthesia and refinements in surgical technique. It is the responsibility of the physician to delineate the cause of lung abscess.
Despite adequate work-up, in 15-20% cases of lung abscess the aetiological mechanism is elusive.
This study was undertaken with the object of studying the aetiological aspects of lung abscess namely predisposing factors, bronchopulmonary segments involved and the causative organisms.
Thirty patients of lung abscess admitted to Medical College Hospital Aurangabad, between August, 1978 and July, 1980 were studied. In all cases a penetrating history especially directed at delineating the causative mechanism for the production of lung abscess was taken (i.e. history of dental extraction, sinusitis, bronchiectasis, pneumonia, malignancy, anycoma, anaesthesia, alcoholism, epilepsy, electro-convulsive therapy, etc.).
Dental examination was done by the hospital's dental staff.
Lung abscess was diagnosed as any cavity with a fluid level in the chest X-ray, tuberculosis being excluded.
Tuberculosis was excluded in all cases by looking for Acid Fast Bacilli by Petroff's concentration method. Sputum was also seen for malignant cells by Papanicolaou stain. X-ray chest (P.A. and lateral views) was done in all cases. Bronchoscopy was done in 24 cases under local anaesthesia and the aspirate aerobically cultured immediately.
Bronchography was done in 10 cases.
Twenty one patients were males, and 9 females. Nine cases (30%) were in the 4th decade of life and eight (26.6%) were in the 5th. Eighteen patients (60%) belonged to poor socio-economic group.
Thirteen patients (43.3%) were smokers. There were 10 patients (33.3%) who regularly consumed alcohol.
This had isolated beta hemolytic streptococci in 14 cases (46.6%) and staphylococci (coagulase positive) in an equal number. Klebsiella was grown in 8 cases (26.6%), D. pneumoniae in 5 cases (16.6%) and E. coli in 3 cases (10%). Multiple organisms were grown in 12 cases (40%).
Bronchoscopy was done in 24 cases (80%) by a rigid bronchoscope. No case showed a growth, foreign body, bronchostenosis, ulcer or an anatomical abnormality.
In 11 cases (45%), the culture of the bronchoscopic aspirate showed beta hemolytic streptococci. In nine cases (37%), coagulase positive staphylococci were isolated. Klebsiella occurred in 6 cases (25%). D. pneumoniae and E. coli occurred in 2 cases each (8%) and Pseudomonas in 1 case (4%). Three cases showed sterile cultures.
Involvement of the lobes
Three patients (10%) had multiple-lobe involvement. Twenty-seven (90%) had one lobe involvement. Of these 27 cases, 16 patients (53.312) had lung abscess on the right side, and 11 patients (36.6%) had it on the left. Right upper lobe was involved in 9 cases (30%), right middle lobe in 3 cases (10%) and right lower lobe in 4 cases (13.3%). The left upper lobe was involved in 4 cases (13.3%) and the left lower lobe was affected in 7 cases (23.3%).
The posterior segment of the right upper lobe was involved in 3 cases (10%) and the anterior segment of the same lobe in 4 cases (13.3%). The apical segment of right lower lobe was involved in one case (3.3%)
Predisposing causes of lung abscess
Out of 30 cases, predisposing causes were found in 23 cases (76.6%). In 6 cases (20%) dental sepsis was severe enough to be the aetiological cause by itself. In 4 cases (13.3%), alcoholic intoxication had caused lung abscess. There were two cases (6.6%) each of Klebsiella pneumoniae, diabetes, bronchogenic carcinoma and amoebic liver abscess causing lung abscess. There was one case each (3.3%) of septicemia secondary to corticosteroid therapy, staphylococcal pneumonia, epilepsy, bronchiectasis, and sinusitis. In 7 cases (23.3%), no predisposing cause could be found out for the lung abscess.
In the present study the right lung was involved oftener than the left, [16 cases (53.3%) to 11 cases (36.6%), the R: L ratio being 3:2]. This is consistent with reports from the literature.,  Bernhard had collected 501 cases of lung abscess from the literature. There were 35.2% right upper lobe abscesses, 25.5% right lower lobe abscesses, and 13.3%left lower lobe abscesses.
In the present study the posterior segment of the right upper lobe was involved in 3 cases (10%). In the literature this segment is seen to be involved oftener e.g. Schweppe et al -24%, Barnett and Herring-40%. Similarly in the present study the apical segment of the right lower lobe was affected in only one case (3.3%). Again Schweppe et al (13%) and Barnett and Herring (14,%) report a higher incidence of affection. In the present study, the anterior segment of the right upper lobe was involved in 4 cases (16.5%.). Schweppe et al and Barnett and Herring report a lesser incidence, 10% and 8% respectively.
The significance of this striking difference cannot be adequately explained at present because of the small sample size.
The incidence of lobar affection of lung abscess as found by various authors has been presented in [Table 1]
The yield of organisms on sputum culture in this study is consistent with that reported in the literature.,  In 12 cases (40%), there was a mixed flora.
Correlation of sputum culture with bronchoscopic culture
Sputum culture had isolated the same organisms as the bronchoscopic aspirate did, in 12 cases (correlation coefficient 50%).
No case of post-operative lung abscess was found. None occurred after dental extraction or tonsillectomy. Similar observations were noted by Das.
Dental sepsis, severe enough to be the sole aetiological factor was found in 20%. This is consistent with Brock (18.8% ) and Shafron and Tate (28%).
In 4 patients (13.3%) in this series, alcoholic intoxication must have carried a septic embolus from the oral cavity to the lungs during the inebriated state and caused lung abscess. Shafron and Tate implicated alcoholic intoxication in 50%, and Barnett and Herring in 42% of cases of lung abscess.
Lung abscesses secondary to bronchogenic carcinoma are reported in the literature in 2 to 25% cases of lung abscess. In the present study, there were 2 cases (6.6%) of lung abscess secondary to bronchogenic carcinoma.
Amoebic liver abscess bursting into the lung and causing lung abscess is often reported from tropics. There were 2 cases (6.6%) in this study. Wig and Agrawal and Agrawal[l] have reported one case each in their series while Vigg and Sahay have reported 3 cases in their study. Other predisposing causes were diabetes 2 cases (6.6%), epilepsy, steroid therapy, sinusitis and bronchiectasis one each (3.3%)
In the present study, there were 7 cases (23.3%) in whom no predisposing cause could be found for lung abscess. This is probably due to the limitations of facilities for diagnostic work-up.