Page 491 - Textbook of Pathology, 6th Edition

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2. Non-sterile aspirate causes widespread broncho-
pneumonia with multiple areas of necrosis and suppu-
ration. A granulomatous reaction with foreign body giant
cells may surround the aspirated vegetable matter.

Hypostatic Pneumonia
Hypostatic pneumonia is the term used for collection of
oedema fluid and secretions in the dependent parts of the
lungs in severely debilitated, bed-ridden patients. The
accumulated fluid in the basal zone and posterior part of
lungs gets infected by bacteria from the upper respiratory
tract and sets in bacterial pneumonia. Hypostatic pneumonia
is a common terminal event in the old, feeble, comatose
patients.
Figure 17.13 Common locations of lung abscess. A, Primary lung
Lipid Pneumonia abscess—mostly single, large, commonly due to aspiration, located most
frequently in the lower part of right upper lobe or apex of right lower lobe.
Another variety of non-infective pneumonia is lipid B, Secondary lung abscesses—mostly multiple, small, most commonly
pneumonia which is of 2 types: exogenous and endogenous. post-pneumonic or following septic embolism.
1. Exogenous lipid pneumonia. This is caused by aspiration
of a variety of oily materials. These are: inhalation of oily are introduced into the lungs from one of the following
nasal drops, regurgitation of oily medicines from stomach mechanisms:
(e.g. liquid paraffin), administration of oily vitamin 1. Aspiration of infected foreign material. A number of
preparation to reluctant children or to debilitated old foreign materials such as food, decaying teeth, gastric
patients. contents, severely infected gingivae and teeth, and necrotic CHAPTER 17
2. Endogenous lipid pneumonia. Endogenous origin of tissue from lesions in the mouth, upper respiratory tract or
lipids causing pneumonic consolidation is more common. nasopharynx may be aspirated. This occurs particularly in
The sources of origin are tissue breakdown following favourable circumstances such as during sleep,
obstruction to airways e.g. obstruction by bronchogenic unconsciousness, anaesthesia, general debility and acute
cancer, tuberculosis and bronchiectasis. alcoholism.
2. Preceding bacterial infection. Preceding broncho-
MORPHOLOGIC FEATURES. Grossly, the exogenous pneumonia in a debilitated patient may develop into lung
lipid pneumonia affects the right lung more frequently abscess. Other infective conditions like tuberculosis,
due to direct path from the main bronchus. Quite often, bronchiectasis and mycotic infections may occasionally result
the lesions are bilateral. The affected part of the lungs is in formation of lung abscess.
consolidated. Cut surface is characteristically ‘golden 3. Bronchial obstruction. An abscess may form distal to an The Respiratory System
yellow’. obstructed bronchus such as from bronchial tumour or from
Microscopically, the features are as under: impacted foreign body.
i) Lipid is finely dispersed in the cytoplasm of
macrophages forming foamy macrophages within the 4. Septic embolism. Infected emboli originating from
alveolar spaces. pyaemia, thrombophlebitis or from vegetative bacterial
ii) There may be formation of cholesterol clefts due to endocarditis may be disseminated in the venous circulation
liberation of cholesterol and other lipids. and reach the right side of the heart from where they are
iii) Formation of granulomas with foreign body giant cells lodged in the lung and result in multiple abscesses.
may be seen around the large lipid droplets. 5. Miscellaneous. Rarely lung abscesses may occur from
following causes:
LUNG ABSCESS i) Infection in pulmonary infarcts.
ii) Amoebic abscesses due to infection with Entamoeba
Lung abscess is a localised area of necrosis of lung tissue histolytica.
with suppuration. It is of 2 types (Fig. 17.13): iii) Trauma to the lungs.
Primary lung abscess that develops in an otherwise normal iv) Direct extension from a suppurative focus in the
lung. The commonest cause is aspiration of infected material. mediastinum, oesophagus, subphrenic area or spine.
Secondary lung abscess that develops as a complication of MORPHOLOGIC FEATURES. Abscesses due to aspira-
some other disease of the lung or from another site. tion are more likely to be in right lung due to more vertical
main bronchus and are frequently single. They are
ETIOPATHOGENESIS. The microorganisms commonly commonly located in the lower part of the right upper
isolated from the lungs in lung abscess are streptococci, lobe or apex of right lower lobe. Abscesses developing
staphylococci and various gram-negative organisms. These