Pathologic Principles

It is extremely important to have a good understanding of Pathological processes that occur if one desires to pick them up by physical exam. Each organ or tissue responds in only certain ways for offending agents. Same type of pathological responses are often seen with different etiologies.

The Lungs - Diffuse

• Alveolar
  In this pathological process the alveoli, diffusely in both lungs are filled with either water (pulmonary edema), blood or inflammatory exudate. The interstitium is normal. Hyaline membrane can form along alveolar wall. The elastic recoil increases and the size of the lung decreases. There is decreased compliance and lung expansion decreases.
• Interstitial
  The interstitium consists of lymphatics, capillary bed . Diseases of any of these structures can cause thickening. Water (pulmonary edema), lymphatic engorgement, blood, inflammatory exudate and fibroblasts can be the cause for the thickening. Lung becomes heavy. The elastic recoil increases resulting in smaller lung. Lungs become stiff and expansion decreases.

Localized

• Consolidation
  The process involves a segment or a lobe. The alveoli are filled with inflammatory exudate. Pneumonia goes through stage of red hepatization when the alveoli are predominantly filled with red cells. Polymorphs and organisms can be seen in the alveoli. The visceral pleura becomes irregular and inflamed. The size of the lobe initially slightly swells and gradually decreases slightly. There is no significant loss of lung volume in consolidation. the airways are patent except for mucus or pus in the stage of resolution. Depending on the nature of offending organism or agent there may be necrosis of lung tissue.
• Atelectasis
  Atelectasis means alveoli devoid of air. There are four types of atelectasis.
  1. Absorptive: When there is airway occlusion, there is no more ventilation to lung beyond obstruction. Gradually the air gets absorbed by the pulmonary circulation. The lung collapses. This results in loss of lung volume on that side.
  2. Relaxation: The lung is held in opposition to chest wall because of the negative pressure in the pleural space. Once this negative pressure is lost as in pneumothorax or effusion the lung relaxes to its resting state.
  3. Adhesive: Alveoli are kept open by surfactant. If for any reason the surfactant is depleted the alveoli collapse. In ARDS there is diffuse adhesive atelectasis. In pulmonary embolism you get plate like atelectasis due to loss of CO2 and surfactant.
  4. Contractile: In fibrosis the alveoli are squeezed out of their air.

Mass

This is a space occupying lesion. There is no lung architecture. The cut surface is homogenous. Margins are sharp. The lesion may not respect fissures. The lesion can infiltrate invade or compress surrounding structures.

Cavitation

Cavity is a hole in the lung. It has wall which can be made up of necrotic tumor or inflammatory mass. The lumen may be irregular. it can be either empty or filled with pus, blood, necrotic debris, or fungus ball. The cavity can be completely filled. There may or may not be a communication to bronchus.

Fibrosis

The lung is focally fibrotic. There is loss of lung volume.

Congestion

The bases of lungs are congested and heavy.

Distension

In patients with COPD, Asthma and Emphysema the alveoli are dilated or distended. The lungs are larger either due to loss of elastic recoil as in emphysema or due to air trapping as in Asthma. There may be blebs in Emphysema. Most of these blebs are superficial and along the upper lobes.

Airways

• Obstruction
• Dilatation
• Inflammation

Pleura

• Effusion
• Pneumothorax
• Pleurisy
• Fibrosis
• Pleural masses

Mediastinum

• Mass
• Air
• Inflammation

Chest Wall

• Deformity
• Mass
• Inflammation