Systemic Pathology ISystemic Pathology IVPM 221

PATHOLOGY OF THE

PERITONEUM

November 2008

i l i i l l di id d i b

Normal structure and function• peritoneal cavity incompletely divided into compartments by

mesentery, omentum and ligaments, which are all lined by mesothelium; surface area greater than that of the skin;; g ;

• normal peritoneum: smooth, shiny membrane with just enough fluid to keep it moist;

• fibrinolytic activity of mesothelium;• resident population of

h l i h d bmacrophages, replenished by blood monocytes;

Normal structure and function (cont’d)

• partial compartmentalization of peritoneal cavity + adhesive ability and blood supply of omentum / mesentery → possible sequestration of bacterial infections;

• ascites (hydroperitoneum), due to d ti di i i h d loverproduction or diminished removal

of intraperitoneal fluid;• hemoperitoneum in acute• hemoperitoneum in acute

traumatic injury;• peritonitis.peritonitis.

AscitesHemoperitoneum

Chylous ascites

Damage to adipocytes → formation of soaps free cholesterol free

Abdominal fat necrosis (steatonecrosis)Damage to adipocytes → formation of soaps, free cholesterol, free radicals → marked inflammation, acute (hyperemia, neutrophils, cellular debris) to chronic (macrophages, multinucleated giant cells, fibrosis).

1. Enzymatic Fat Necrosis.

Abdominal fat necrosis (cont’d)y

acute pancreatic necrosis releases proteolytic and lipolytic enzymes;grossly:

• multifocal to confluent white masses of necrotic adipose tissue, associated with inflammatory reaction (hyperemia fibrin);associated with inflammatory reaction (hyperemia, fibrin);

• peripancreatic and, possibly, distant locations.Multifocal fat necrosis (white areas) disseminated throughout the abdominal fat, pancreatitis, cat.

2. Multifocal Fat Necrosis.especially in fat sheep occasionally in other species;especially in fat sheep, occasionally in other species;pathogenesis: probably related to pressure ischemia (necrosis) of the fat and subsequent inflammation;grossly: small, white, dry, firm or gritty plaques associated with chronic inflammation.

(bovine –perirenal fat)

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3. Massive Fat Necrosis (diffuse lipogranulomatosis).

especially in fat cattle of the Channel Island breedsespecially in fat cattle of the Channel Island breeds.

pathogenesis: increased production of saturated fatty acids in rumen → fat stores solid at body temperature → prone to trauma / ischemic → at sto es so d at body te pe atu e → p o e to t au a / sc e cnecrosis.

grossly: hard masses of necrotic fat in abdomen and elsewhere; incidental, or may cause intestinal obstruction, compression of ureters, or dystocia.

seen in many species.Steatitis (yellow fat disease)

y p

diet high in polyunsaturated fat and low in vitamin E, allowing peroxidation of body fatty acids (e.g. cats on all-fish diet).

all fat stores are affected (= pansteatitis, including panniculitis).

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Great blue heron – pansteatitis? or massive fat necrosis secondary to obesity?secondary to obesity?

cross section of stomach and perigastric fat

Inflammation - peritonitis

Very common in large animals less so in dogs and cats;Very common in large animals, less so in dogs and cats;

most often caused by bacteria, but also viruses, helminths and chemicals (e.g. bile, pancreatic enzymes);c e c s (e.g. b e, p c e c e y es);

classified as: primary or secondary, acute or chronic, localized or diffuse, septic or nonseptic;

Inflammation - peritonitis (cont’d)

common causes:

► bacteremia / septicemia, particularly in young animals:

serosal surfaces (peritoneum, pleura, pericardium), synovial membranes of joints, and meninges normally have a large population of macrophages replenished by blood monocytes; in young animalsof macrophages, replenished by blood monocytes; in young animals, monocytes phagocytize well but have limited bactericidal power, and they end up transporting bacteria from other sites (e.g.

h li i b ) h iomphalitis, mucous membranes) to these sites;

► intestinal accident;

► perforated viscera (stomach / abomasum, reticulum, uterus);

if the animal survives, sequelae may include fibrous adhesions / intestinal obstruction.

• high capacity for sequestration of infections;Cattlehigh capacity for sequestration of infections;

• common causes: omphalophlebitis / septicemia (newborns);perforated reticulum / abomasum / uterus.p

Acute: hyperemia / h h/ hemorrhage; fibrin, (fibrinous peritonits), cow

Cattle Rupture of liver abscesses causes septic peritonitis

subacute / chronic fibrinopurulent peritonitis – hardware (adult)

subacute / chronic fibrinopurulent peritonitis –perforated abomasal ulcer (calf)

• poor capacity for sequestration of infections;ll d f l

Horse

• usually acute and fatal;• common causes: rupture of stomach;

intestinal accident (torsion volvulus sequestration);intestinal accident (torsion, volvulus, sequestration);• septicemia in foals: Rhodococcus equi, Actinobacillus equuli.

l i i ( lib ill i )

Pig

• neonatal septicemia (e.g. colibacillosis);• fibrinous / fibrinosuppurative peritonitis (and polyserostitis / arthritis),

e g Hemophilus parasuis (Glasser’s disease) Mycoplasma sppe.g. Hemophilus parasuis (Glasser s disease), Mycoplasma spp., Streptococcus suis type 2.

Dog, CatFocal foreign body (granulomatous) reaction (forgotten gauze)

• nocardiosis;• uterine rupture, intestinal accidents.

Perforated gastric ulcers in a dog.

Nocardiosis, note the yellow granular material (“sulfur granules”)

characteristic of this condition

Feline infectious peritonitisp

incidence is low and sporadic;• caused by feline coronaviruses – broad spectrum of virulence,

i i l f fspontaneous mutations are common → potential for emergence of more virulent strains;

• persistently infected healthy cats carry the virus in their intestinepersistently infected healthy cats carry the virus in their intestine, blood and tissues - reservoirs;

• disease is more common in young and aged cats, especially in environments with close continuous contact among many cats.

Feline infectious peritonitis

Pathogenesis:

• ingestion or inhalation of FCoV → replication in tonsils, intestinal gest o o a at o o CoV → ep cat o to s s, test aepithelium, mesenteric lymph nodes → hematogenous spread and some replication in monocytes / macrophages;

• ability of individual strains of FCoV to cause disease appears to correlate with their ability to invade and replicate in monocytes / macrophages;macrophages;

• animal’s immune response, i.e humoral vs cell-mediated, determines outcome of infection;;

• immune-complex disease → vasculitis;

• activated macrophages may have central in development of lesions• activated macrophages may have central in development of lesions.

Effusive form:• serofibrinous peritonitis (up to 1 litre of exudate) and pleuritis; p ( p ) p ;• fluid is clear, viscous, pale to deep yellow, and contains fibrin strands; • foci of necrosis or inflammatory nodules on serosal surfaces of viscera.

Marked abdominal distension due to the presence of fluid FIPMarked abdominal distension due to the presence of fluid, FIP, effusive form.

Effusive form (cont’d)

Both examples (top and left bottom) show abundant clear yellow fluidshow abundant clear yellow fluid

and abundant fibrin deposited on the serosal surface

White foci of necrosis or nodules areSometimes present on serosal surfaces of

visceral organs

Effusive form (cont’d): vasculitis - fibrinoid necrosis of several arterioles, necrosis of tissue (mesenteric lymph node).( y p )

Noneffusive form:• nodular to locally extensive pyogranulomatous inflammation innodular to locally extensive pyogranulomatous inflammation in

several organs;• less severe peritoneal exudate.

Examples of pyogranulomatous nephritis resembling neoplasticlesions (lymphoma), cats, FIP, dry form.

Noneffusive form (cont’d): meningitis, with vasculitis

Noneffusive form (cont’d): myocarditis, with vasculitis

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Neoplasia Mesothelioma

• rare malignant tumor; seen most commonly as congenital neoplasia in calves;• spread is usually by exfoliation / implantation, rather than by blood / lymph;• must be differentiated from granulomatous peritonitis (e.g. tuberculosis) or

secondary neoplasia (e.g. carcinomatous implantation).

• common in horses; arises from the mesentery, often large and Lipoma

; y, gpedunculated;

• can cause intestinal strangulation when peduncle winds around

Lipoma (cont’d)can cause intestinal strangulation when peduncle winds around

loop of intestine.

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• Usually arise from exfoliation / implantation rather than by

Secondary tumorsUsually arise from exfoliation / implantation, rather than by lymphogenous or hematogenous metastasis;

• carcinomas are more common than sarcomas.

Uterine carcinoma with metastases to the omentum, bovine

Peritoneal carcinomatosis3 examples of direct seeding of the peritoneal surface (cavity)

in two dogs (left) and a chicken (top right)

Disseminated hemangiosarcoma (omentum), dog