Lobar pneumonia is a form of

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severi ...

characterized by inflammatory exudate within the intra-alveolar space resulting in consolidation that affects a large and continuous area of the lobe of a lung. It is one of three anatomic classifications of pneumonia (the other being

bronchopneumonia Bronchopneumonia is a subtype of pneumonia. It is the acute inflammation of the bronchi, accompanied by inflamed patches in the nearby lobules of the lungs. citing: Webster's New World College Dictionary, Fifth Edition, Copyright 2014 It is ofte ...

and

atypical pneumonia Atypical pneumonia, also known as walking pneumonia, is any type of pneumonia not caused by one of the pathogens most commonly associated with the disease. Its clinical presentation contrasts to that of "typical" pneumonia. A variety of microorgan ...

). In children round pneumonia develops instead because the pores of Kohn which allow the lobar spread of infection are underdeveloped.

Mechanism

The invading organism starts multiplying, thereby releasing toxins that cause inflammation and edema of the lung parenchyma. This leads to the accumulation of cellular debris within the lungs. This leads to consolidation or solidification, which is a term that is used for macroscopic or radiologic appearance of the lungs affected by pneumonia. Bacterial pneumonia is mainly classified into lobar and diffuse depending on the degree of lung irritation or damage.

Stages

Lobar pneumonia usually has an acute progression. Classically, the disease has four stages: * Congestion in the first 24 hours: This stage is characterized histologically by vascular engorgement, intra-alveolar fluid, small numbers of neutrophils, often numerous

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

. Grossly, the lung is heavy and hyperemic. * Red hepatization or consolidation: Vascular congestion persists, with extravasation of red blood cells into alveolar spaces, along with increased numbers of

neutrophil Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying ...

s and fibrin. The filling of airspaces by the exudate leads to a gross appearance of solidification, or consolidation, of the alveolar parenchyma. This appearance has been likened to that of the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

, hence the term "hepatization". * Grey hepatization: Red blood cells disintegrate, with persistence of the neutrophils and fibrin. The alveoli still appear consolidated, but grossly the color is paler and the cut surface is drier. This is when death typically occurs in severe cases. * Resolution (complete recovery): The exudate is digested by enzymatic activity, and cleared by macrophages or by cough mechanism. Enzymes produced by neutrophils will liquify exudates, and this will either be coughed up in sputum or be drained via lymph.

In children

The openings between the alveoli known as the pores of Kohn, and the collateral airways of the

canals of Lambert Collateral ventilation (CV) is a back-up system of alveolar ventilation that can bypass the normal route of airflow when airways are restricted or obstructed. The pathways involved include those between adjacent alveoli ( pores of Kohn), between br ...

, are undeveloped in children. Spread of infection that would otherwise occur is prevented and can result in round pneumonia, most commonly caused by '' S. pneumoniae''. This clinically presents with an initial mild respiratory infection, followed by

fever Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...

. On

imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of an image). Imaging technology is the application of materials and methods to create, preserve, or duplicate images. ...

it presents an opaque pulmonary consolidation which is unusually round, and can resemble a lung mass. However it quickly resolves with antibiotics.

Diagnosis

The most common organisms which cause lobar pneumonia are ''

Streptococcus pneumoniae ''Streptococcus pneumoniae'', or pneumococcus, is a Gram-positive, spherical bacteria, alpha-hemolytic (under aerobic conditions) or beta-hemolytic (under anaerobic conditions), aerotolerant anaerobic member of the genus Streptococcus. They ar ...

'', also called pneumococcus, ''

Haemophilus influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative, non-motile, coccobacillary, facultatively anaerobic, capnophilic pathogenic bacterium of the family Pasteurellaceae. The bacter ...

'' and ''

Moraxella catarrhalis ''Moraxella catarrhalis'' is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system, and joints of humans. It causes the inf ...

''. '' Mycobacterium tuberculosis'', the tubercle bacillus, may also cause lobar pneumonia if pulmonary

tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, i ...

is not treated promptly. Other organisms that cause lobar pneumonia are Legionella pneumophila and

Klebsiella pneumoniae ''Klebsiella pneumoniae'' is a Gram-negative, non-motile, encapsulated, lactose- fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar. Although found in the normal flora of the mo ...

. Like other types of pneumonia, lobar pneumonia can present as community acquired, in immune suppressed patients or as nosocomial infection. However, most causative organisms are of the community acquired type. Pathological specimens to be obtained for investigations include: # Sputum for culture, AAFBS and gram stain # Blood for full hemogram/complete blood count, ESR and other acute phase reactants # Procalcitonin test, more specific On a posteroanterior and lateral chest radiograph, an entire lobe will be radiopaque, which is indicative of lobar pneumonia. File:X-ray of lobar pneumonia.jpg, Chest radiograph of a lobar pneumonia, affecting the right middle lobe. File:CT of lobar pneumonia.jpg, CT scan of the same case. The identification of the infectious organism (or other cause) is an important part of modern treatment of pneumonia. The anatomical patterns of distribution can be associated with certain organisms, and can help in selection of an antibiotic while waiting for the pathogen to be cultured.

References

External links

* {{Respiratory pathology Pneumonia