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 severity ...

characterized by inflammatory exudate within the intra-alveolar space resulting in consolidation that affects a large and continuous area of the

lobe Lobe may refer to: People with the name * Lobe (surname) Science and healthcare * Lobe (anatomy) * Lobe, a large-scale structure of a radio galaxy * Glacial lobe, a lobe-shaped glacier * Lobation, a characteristic of the nucleus of certain biolo ...

of a lung. It is one of three anatomic classifications of pneumonia (the other being bronchopneumonia 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 The pores of Kohn (also known as interalveolar connections or alveolar pores) are discrete holes in walls of adjacent alveoli. Cuboidal type II alveolar cells, which produce surfactant, usually form part of aperture. Etymology The pores of Kohn tak ...

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 biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. Grossly, the

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

is heavy and

hyperemic Hyperaemia (also hyperemia) is the increase of blood flow to different tissues in the body. It can have medical implications but is also a regulatory response, allowing change in blood supply to different tissues through vasodilation. Clinically, ...

. * 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 in ...

s and

fibrin Fibrin (also called Factor Ia) is a fibrous, non-globular protein involved in the clotting of blood. It is formed by the action of the protease thrombin on fibrinogen, which causes it to polymerize. The polymerized fibrin, together with platele ...

. The filling of airspaces by the exudate leads to a gross appearance of solidification, or consolidation, of the alveolar

parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...

. This appearance has been likened to that of the

liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...

, 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

macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer cel ...

s 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

, 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 bron ...

, 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 ''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 are ...

''. This clinically presents with an initial mild respiratory infection, followed by

fever Fever, also referred to as pyrexia, is defined as having a body temperature, temperature above the human body temperature, normal range due to an increase in the body's temperature Human body temperature#Fever, set point. There is not a single ...

. On imaging 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'', 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 bacteria ...

'' and '' Moraxella catarrhalis''. ''

Mycobacterium tuberculosis ''Mycobacterium tuberculosis'' (M. tb) is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, ''M. tuberculosis'' has an unusual, waxy coating on its c ...

'', 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, in ...

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

Legionella pneumophila ''Legionella pneumophila'' is a thin, aerobic, pleomorphic, flagellated, non-spore-forming, Gram-negative bacterium of the genus ''Legionella''. ''L. pneumophila'' is the primary human pathogenic bacterium in this group and is the causative age ...

and Klebsiella pneumoniae. 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 A chest radiograph, called a chest X-ray (CXR), or chest film, is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in med ...

, an entire lobe will be radiopaque, which is indicative of lobar pneumonia. File:X-ray of lobar pneumonia.jpg,

Chest radiograph A chest radiograph, called a chest X-ray (CXR), or chest film, is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in med ...

of a lobar pneumonia, affecting the right middle lobe. File:CT of lobar pneumonia.jpg,

CT scan A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...

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