The Pathology
of
Appendix and Peritoneum
The Pathology of Appendix
Appendix
The vermiform appendix, which is usually 8 to 10
cm
Has a retrocecal attachment to the cecum, move
freely.
The wall of the appendix is composed of the
same layers as the rest of the intestine.
The most prominent microscopic feature is the
predominance of submucosal lymphoid
tissue.
Acute Appendicitis
This condition is by far the most common disease of the appendix
Most frequent cause of an abdominal emergency
An inflammatory disease of the wall of the vermiform appendix that
leads to transmural inflammation and perforation and peritonitis
Right lower quadrant syndrome
Etiology:
Obstruction of its orifice (50 to 80%)
– Fecalith / Solid fecal material (50%)
– Hyperplastic lymphoid tissue [bacterial or viral infection (e.g., by Salmonella
or measles)]
– Tumor
– Ball of pinworms (Enterobius vermicularis)
– Foreign body (e.g., gallstone)
Pathogenesis:
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Continued mucinous secretion
Progressive increase in intraluminal pressure
Increased venous pressure
Ischemic injury
Mucosal ulceration
Invasion by intestinal bacteria
Additional inflammatory edema and exudation
(neutrophil accumulation  acute suppurative
inflammation)
– Gangrene
Pathology
The appendix is congested, tense, and covered by a fibrinous
exudate.
Its lumen often contains purulent material.
Earliest stage:
– Normal glistening serosa
 a dull, granular, red
membrane
– A scant neutrophilic
exudate
– Congestion
Later stage:
– A prominent neutrophilic
exudate
– Foci of suppurative
necrosis in the mucosa
– Fibrinopurulent reaction
over the serosa
– Abscess formation within
the wall, along with
ulcerations
– Acute suppurative
appendicitis
Acute gangrenous appendicitis
– Large areas of hemorrhagic green ulceration
of the mucosa
– Green-black gangrenous necrosis through the
wall, extending to the serosa,
– Rupture (perforation)  Suppurative
peritonitis
perforation of the wall releases the luminal
contents into the peritoneal cavity
Complications
Periappendiceal abscesses (anywhere in the abdominal cavity)
Fistulous tracts (the small and large bowel, bladder, vagina, or
abdominal wall)
Superior mesenteric vein syndrome
– Pylephlebitis (thrombophlebitis of the intrahepatic portal vein)
– Secondary hepatic abscesses
Perforation and diffuse peritonitis
Septicemia
Wound infection after surgery
– in patients with perforation and periappendiceal abscess
Mucocele
A dilated mucus-filled appendix (bag of
mucus)
Etiology:
– Neoplastic
mucin-producing adenoma (mucinous cystadenoma)
mucinous cystadenocarcinoma
– Non-neoplastic
chronic obstruction
Complications
Infection
Rupture (perforation)
– discharging mucin and debris into the
peritoneum  localized collections of mucus
attached to the serosa (without tumor cells)
Pseudomyxoma peritonei
– Cystadenoma or Cystadenocarcinoma 
perforation  seeding of the peritoneum by
mucus-secreting tumor cells
In less than one third of cases, pseudomyxoma
peritonei is caused by disease of the appendix
In half, it originates from ovarian mucinous
cystadenocarcinoma
Tumors
Carcinoid
– Common
– Small ones do not metastasize
they do if they are over 1.5 cm, which is very rare
The Pathology of Periton
The peritoneum is the mesothelial lining of the abdominal cavity and its
viscera
Peritonitis
Peritonitis results in an acute abdomen
Classification and Etiology
Bacterial peritonitis
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Perforation (appendicitis, cholecystitis, diverticulitis, salpingitis, ect.)
Ileus (intestinal obstruction, blunt abdomial trauma)
Iatrogenic (surgery: infected surgical instruments&environment)
Penetrating wounds (bullet, knife, stab, blown from an explosion,
falling on a sharp object)
– Bacterial invasion of ascites (spontaneous bacterial peritonitis)
Chemical peritonitis
– Sterile (bile) peritonitis:
perforated gallbladder
needle biopsy of the liver
– Perforated peptic ulcer (stomach or duodenum)
Hydrochloric acid
Hemorrhage
– Acute hemorrhagic pancreatitis
release and activation of potent lipolytic and proteolytic enzymes
Severe peritonitis and fat necrosis
Globules of free fat may be found floating in the peritoneal fluid, and
bacterial permeation of the bowel wall leads to a frank suppurative exudate
after 24 to 48 hours.
– Chemicals introduced by surgery
Talc
Some chemical in the dialysate
Gynecologic conditions
– Endometriosis (blood into the peritoneal cavity)
– Ruptured dermoid cysts (peritoneal granulomatous reaction)
Pathogenesis
PERFORATION
– Inflamed appendix
– Peptic ulcer
– Colonic diverticulum
– Cholecystitis
– Strangulation of bowel
– Acute salpingitis
Acute abdomen
– Severe abdominal pain and tenderness
– Nausea, vomiting, and a high fever
– Severe cases  generalized peritonitis, paralytic ileus, and
septic shock
– Often the perforation becomes “walled off” in which case a
peritoneal abscess results.
Origin of organisms:
– GIS: E. coli, streptococci, Staphylococcus aureus, enterococci,
gram-negative rods, Clostridium perfringens
– Genital system: gonococcus and Chlamydia
CHRONIC PERITONEAL DIALYSIS
Contamination of instruments or dialysate
Staphylococci, Streptococci
One fourth of cases are aseptic
Caused by some chemical in the dialysate
SPONTANEOUS BACTERIAL PERITONITIS
No appearent cause (such as a perforated viscus)
Risk factors: Ascites
– Cirrhosis (adults): enteric bacilli
– Nephrotic syndrome (children): urinary tract infections
TUBERCULOUS PERITONITIS
An uncommon site of extrapulmonary TB infection
Risk factors:
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Cirrhosis
HIV infection
Diabetes mellitus
Malignancy (treatment with TNF agents)
Pathogenesis:
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Reactivation of latent tuberculous foci
Hematogenous spread
Infected small intestine
Tuberculous salpingitis
Pathology
A fibrinopurulent exudate covers the surface of the
intestines
Organization of exudate  adhesions (between loops of
bowel)
– adhesions may be lysed
– may lead to volvulus and intestinal obstruction
Bacterial salpingitis
– Gonococcal
– may lead to pelvic peritonitis and adhesions  pelvic inflammatory
disease
Familial Paroxysmal Polyserositis
(Familial Mediterranean Fever - FMF)
Peritonitis and Amyloidosis
Inherited autosomal recessive disorder
Recurrent episodes of aseptic peritonitis with
fever and abdominal pain
Arthritis and pleuritis at some time
The disease predominates in Sephardic Jews
and other Mediterranean populations, such as
Armenians, Turks, and Arabs
The pathogenesis of FMF remains obscure
Retroperitoneal Fibrosis
Dense fibromatous overgrowth of the retroperitoneal tissues
Sclerosing retroperitonitis or idiopathic retroperitoneal fibrosis (also
called Ormond disease).
Uncommon
Fibrosing condition of the abdomen, becomes symptomatic when it
causes obstruction of the ureters
Inflammatory infiltration (lymphocytes, plasma cells, and neutrophils)
Hydronephrosis
Cystic Lesions and Neoplasms of
the Peritoneum
Mesenteric and Omental Cysts
– Large to small cystic masses
(1) arising from sequestered lymphatic channels (mesenteric and omental
cysts are usually of lymphatic origin)
(2) derived from pinched-off enteric diverticula of the developing foregut
and hindgut
(3) derived from the urogenital ridge or its derivatives (i.e., the urinary tract
and male and female genital tracts)
(4) derived from walled-off infections or following pancreatitis, more
properly called pseudocysts
(5) malignant origin (intra-abdominal adenocarcinomas)
– Complications:
rupture
bleeding
torsion
intestinal obstruction
Primary tumors
Mesotheliomas
Most common primary peritoneal tumor
Asbestos exposure (80%)
The pathologic characteristics of peritoneal
mesotheliomas are identical to those of their
pleural counterparts
Secondary tumors
Metastatic Carcinoma
Quite common
Ovarian and pancreatic cancers
– penetration to the serosal membrane or metastatic
seeding (peritoneal carcinomatosis)
Appendiceal mucinous carcinomas
– pseudomyxoma peritoneii
Extra-abdominal locations
– may be implicated in peritoneal seeding