Appendicular abscess pathophysiology

An appendicular abscess is a complication of acute appendicitis. It is resulted due to the invasion of the appendix by bacteria following an obstruction. The appendix exists at the junction of the small and large intestine and is a natural habitat of wide variety of bacteria. It is, therefore, prone to develop complications when blocked. Coupled with an infection, acute appendicitis can be life threatening. Other serious complications which may develop as a result of neglected appendicitis or appendicular abscess include gangrene, appendicular masses, rupture, and general peritoneal infections.

• Obstruction of the tubular space inside the appendix is the main inciting event, this initial problem leads to the inflammation of the appendix, obstruction of the blood vessels supplying it, and finally infection.^[1]
• Once these blood vessels are obstructed, appendiceal tissue starts to die and leak out its cellular components.^[2]
• This leads to an increase in endoluminal and intramural pressure, which can result in an occlusion of the venules in the appendiceal wall resulting in thrombosis and occlusion and stasis of blood and lymphatic flow.
• The stasis favors the bacterial growth leading to infection of the appendix.
• Inflammatory mediators along with various bacterial toxins and proteolytic enzymes from the neutrophils are released, resulting in the formation of abscess in appendix.

• The abscesses usually contain a mixture of aerobic and anaerobic bacteria from the gastrointestinal tractt.

• The risk of perforation or abscess formation is negligible within the first 12 hours of untreated symptoms, but then increases to 8.0% within the first 24 hours.^[1]

• The serosal surface of the appendix may appear pale with rough edges and yellowish exudate along with hyperemia.

• A focally necrotic appendiceal debris is seen in the mucosal wall.
• Intravascular fibrin is seen in medium-sized blood vessels.
• Clusters of neutrophils are seen on the serosal aspect.