Consolidation is a clinical term for solidification into a firm, dense mass. It is more specifically used in reference to a region of lung tissue that, normally compressible, has filled with liquid, a condition marked by induration (swelling or hardening of normally soft tissue) of a normally aerated lung

Lung

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

. Consolidation occurs through accumulation of inflammatory cellular exudate in the alveoli and adjoining ducts. Simply, it is defined as alveolar space that contains liquid instead of gas. The fluid can be pulmonary edema, inflammatory exudate, pus, inhaled water, or blood (from bronchial tree or haemorrhage from a pulmonary artery). It is clinically important in pneumonia

Pneumonia

Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

: the signs of lobar pneumonia are characteristic and clinically referred to as consolidation.

Signs

Signs that consolidation may have occurred include:

• Expansion of the thorax on inspiration is reduced on the affected side
• Vocal fremitus is increased on the side with consolidation
• Percussion is dull in affected area
• Breath sounds are bronchial
• Possible medium, late, or pan-inspiratory crackles
• Vocal resonance is increased. Vocal resonance testing can be done with a stethoscope. Here, the patient's voice (or whisper, as in whispered pectoriloquy
  Whispered pectoriloquy
  Whispered pectoriloquy refers to an increased loudness of whispering noted during auscultation with a stethoscope on the lung fields on a patient's back.Usually sounds of this volume would not be heard when whispered...
  
  ) can be heard more clearly when there is consolidation, as opposed to in the healthy lung where speech sounds muffled.
• A pleural rub may be present

Radiology

• Typically, an area of white lung is seen on a standard X-ray. Consolidated tissue is radio-opaque, so that it is clearly demonstrable in X-rays and CT (computerized tomography) scans. Consolidation is often a middle-to-late stage feature/complication in pulmonary infections.