Pneumonia 

Definition:-

The term "pneumonia" and "pneumonitis" are synonymous for inflammation of lungs

Pneumonia is defined as acute inflammation of the lung parenchyma distal to the terminal bronchioles(consistting of the respiratory bronchioles, alveolar duct, alveolar sac, and alveoli).

Pathogenesis:-

The microorganisms gain entry in the lungs and cause infection so the mainly 4 route of infection occurs -

1. Inhalation of the microbes these present in air.
2. Aspiration of organisms from the nasopharynx or oropharynx.
3. Haematogenous spread from the distant focus of infection.
4. Direct infection from an adjoining site of infection.

The normally lungs are free from any microbes because of the presence of the "lung defence mechanisms " at the different levels. Such as-

• Nasopharyngeal filtering action 
• Mucociliary action of the lower respiratory airways.
• Presence of phagocytosing alveolar macrophages 
• Immunoglobulins

Failure of these defence mechanisms due to some certain predisposing factors results in pneumonia cause.

Classification of pneumonia:-

On the basis of etiological classification pneumonia classified in 3 main groups-

1. Bacterial pneumonia 
2. Viral pneumonia 
3. Pneumonia from other etiologies.

​​​​​​​1. Bacterial pneumonia:-

Bacterial infection in the lung parenchyma is the most common cause of the pneumonia,or consolidation of one or both the lungs. These divided in two types-

           A.  Lobar pneumonia 

           B.  Broncho (lobular) pneumonia 

A.  Lobar pneumonia:-

Lobar pneumonia is an acute bacterial infection of a part of a lobe, entire lobe,or even two lobes of one or both the lungs.

Mainly caused by-  Streptococcus pneumoniae (90%)

                                   Staphylococcal pneumoniae

                                   Beta- haemolytic streptococci 

                                   Some gram-negative aerobic bacteria 

Histology:- 

Lobar pneumonia shows 4 pathologic phase-

1. Stage of congestion (initial phase)
2. Red hepatisation (early consolidation)
3. Grey hepatisation (late consolidation)
4. Resolution 

​​​​​​​1. Stage of congestion: initial phase 

The initial phase represents the early acute inflammatory response to the bacterial infection for lasts 1 to 2 days.

Grossly:-

The affected lobe is enlarged, heavy, dark-red congestion. Cut surface exudes blood stained frothy fluid.

Microscopically:-

Dilatation and congestion of the capillaries, pale eosinophilic oedema fluid in the air space and numerous bacteria can also be demonstrated.

2. Red hepatisation: early consolidation 

This phase lasts for 2 to 4 days . The term hepatisation in pneumonia means "liver like consistency" 

Grossly:- 

THe affected lobe is red ,firm and consolidated ​​​​​​. The cut surface of affected lobe is airless, red pink,dry, granular and liver like consistency. The red hepatisation is accompanied by "serofibrinous pleurisy".

Microscopically :-

THe oedema fluid is replaced by strands of fibrin. The cellular exudates marked with Neutrophils and extravasation of red cell.

3. Grey hepatisation: Late consolidation 

This phase lasts for 4 to 8 days.

Grossly:-

The affected lobe is firm and heavy and the cut surface is dry, granular and gery liver like consistency. Or fibrinous plurisy is prominent .

Microscopically:-

The fibrin thread is dense and numerous ​​​​​​, the cellular exudates of Neutrophils is reduced due to disintegration of many inflammatory cells.

4. Resolution:-

This stage is begins by 8th or 9th day and it completed in 1 to 3 weeks. Antibiotic therapy can help to induce resolution in the organ.

Grossly:-

The previously formed solid fibrinous constituent is liquefied by the enzymatic activity. And restoring the normal aeration in the affected lobe.

Microscopically:-

Now macrophages are present predominately in the lumen and Neutrophils gets dismissed. Granular and fragmented strand of fibrin get digest by the enzymatic action.

Complication of pneumonia in severe cases:-

• Plural effusion:- fibrous adhesion in between visceral and parietal plura. In some treated patient of lobar pneumonia shows inflammation in plura with effusion.
• Lung abscess:- the rare complication of the lobar pneumonia, specially when secondary infection occurs by the other organisms.
• Empyema:- less then 1% of treated case of lobar pneumonia devloped encysted pus in plural cavity.
• Organisation:- less than 3% of lobar pneumonia resolution will not occur of exudates.

​​​​​​​Clinical features:-

The major symptoms of the lobar pneumonia is- shaking chills, fever ,malaise,chest pain, dyspnoea and cough(purulent or even bloody). Some patients tachycardia, tachypnoea, and sometime cyanosis occurs

Diagnostic findings:-

• Blood culture and sputum culture 
• Chest radiography 
• Antibiotics sensitivity test 

​​​​​​​Treatment:-

​​​​​​​The mainly gives antibiotics in pneumonia, and antibiotics shows rapid actions and clinical improvement within 48 to 72 hours.

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