Lobar pneumonia is a form of pneumonia 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 and atypical pneumonia). 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. 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 neutrophils 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, hence the term "hepatization". Grey hepatization: Red blood cells disintegrate, with persistence of the neutrophils and fibrin.
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 specificOn a posteroanterior and lateral chest radiograph, an entire lobe will be radiopaque, which is indicative of lobar pneumonia. 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
 Media related to Lobar pneumonia at Wikimedia Commons