Acute appendicitis results in
severe acute inflammation of the appendix
Acute appendicitis is a common
cause of abdominal pain.
A predisposing factor is obstruction of the lumen of the appendix, sometimes by
a faecolith, but such obstruction is not seen in all cases.
The complications of acute
• Necrosis of appendix wall
(gangrenous appendicitis), leading to perforation, with subsequent generalized
• Involvement of adjacent
bowel loops, causing perforation of small bowel.
• The omentum may become
adherent, localizing the peritonitis to the right iliac fossa. Fibrosis and
continued inflammation cause development of a mass in the right iliac fossa
(appendix mass). This may resolve with scarring, may form an abscess that drains
to the surface, or may rupture, with development of generalized peritonitis.
• Spread of infection by
portal vein branches may propagate to the liver; this was formerly an important
cause of portal pyaemic abscesses in the liver.
In early acute appendicitis
there is acute inflammation of the mucosa of the appendix which undergoes
Pus may be present in the lumen. At this stage the patient experiences an
ill-defined central abdominal pain.
Macroscopically the appendix is usually swollen and serosal vessels are dilated.
As the acute inflammation develops, it spreads through the full thickness of the
appendix wall to reach the serosal surface.
This causes a localized acute peritonitis, which is perceived as a sharp pain,
localized to the right iliac fossa.
Macroscopically the appendix shows dilated serosal vessels and a rough, yellow,
fibrinous exudate in the surface.
If the appendicitis progresses, there is necrosis of the wall of the appendix
The muscle layer is replaced by an acute inflammatory infiltrate and necrotic
muscle. The resulting weakness leads to appendix perforation, liberating bowel
contents into the peritoneal cavity.
This causes a generalized peritonitis and leads to a severe deterioration in
Macroscopically the appendix is typically plum-coloured or black, and a site of
perforation may be seen.