Cancer of Peritoneum
Primary malignant tumors of the peritoneum (meso-theliomas or endotheliomas) are rare, but secondary malignant tumors are relatively common. Tumor cell spread into the peritoneum occurs by direct extension, hematogenous spread, or lymphatic spread. Once the peritoneum has been invaded, dissemination of malignant cells throughout the peritoneal cavity and implantation diffusely throughout the peritoneal surfaces can occur rapidly. Epithelial primary carcinomas commonly metastasize to the peritoneum (e.g., adenocarcinomas of the stomach, intestine, ovaries, and, less commonly, lung and breast). Melanomas also frequently metastasize to the digestive system, including the mesentery. Malignant neoplasms of the retroperitoneal connective, nervous, or muscular tissue, as well as sarcomas and teratomas, although rare, invade the peritoneum or become metastasized within it.
Mesothelioma,
the most common primary tumor, is a rare, aggressive tumor arising from
mesothelial cells within the serosal lining of the peritoneum, pleura, and
pericardium. Though the cause is unclear, there is a strong association with
asbestos exposure. Peritoneal mesothelioma is classified as either
benign-borderline (multicystic or well-differentiated papillary) mesothelioma
or diffuse peritoneal (epithelial, sarcomatoid, or biphasic) mesothelioma.
Normally,
the peritoneal stromal tissue is a rich source of growth factor and chemokines.
Infiltration of malignant cells often increases exudative secretions and
occludes the lymphatics. Accumulation of excess fluid in the peritoneum, (malignant
ascites) may be serous, serofibrinous, hemorrhagic, or chylous from
malignant fatty degeneration. Chylous pleural effusions, in contrast, are
caused by damage to the thoracic duct or its main tributaries.
Peritoneal
metastases have various morphologic findings, with the gross pattern dependent
on the histology of the primary tumor, manner of spread, and intensity and type
of peritoneal reaction. Most common are nodules scattered over the
omentum, mesentery tissue, and visceral and parietal peritoneum; smaller
nodules, measuring a few millimeters in diameter, are semitranslucent, whereas
larger ones are opaque, white, yellowish white, gray, or reddish. When surface
growth exceeds growth in depth, plaque-like masses develop, which vary
in size and usually have a waxy appearance. Such lesions may be difficult to
detect by even the most accurate cross-sectional imaging. Necrotic changes can
produce ulcer-like depressions and most commonly occur with metastases from
ovarian papillary serous cystadenoma. In the adhesive form, extensive
adhesions may develop in the peritoneal cavity due to organized fibrin bands
produced by dense exudate, the confluence of adjacent implants, or tumor
infiltration from one organ to another. Gastric carcinoma is prone to produce
metastases; many experts recommend peritoneal fluid cytologic analysis before
one attempts extensive surgical resections. When more advanced, such metastases
may merge into a mass that can lead to fistula formation or obstruction. Other
types of peritoneal metastases appear as pedunculated nodules or as small
sessile or pedunculated cysts. The cause is
usually papillary serous cystadenocarcinoma or cystic ovarian tumors.
Metastases of appendicular adenocarcinoma or of ovarian pseudomucinous
cystadenocarcinoma on the peritoneal surfaces may produce pseudomyxoma
peritonei, in which a large quantity of gelatinous material accumulates in
the peritoneal cavity. Rupture of a nonmalignant
mucocele of the appendix with fistula formation may also lead to accumulation
of mucus in the peritoneal cavity.
The
symptoms of peritoneal carcinomatosis are chiefly abdominal distention due to
ascites and abdominal pain but may include weight loss, anorexia, fever, and
diarrhea. Physical examination reveals signs of fluid and, eventually, palpable
masses. The differential diagnosis should consider all chronic peritoneal
conditions. The initial diagnostic procedure is paracentesis for analysis of
fluid, including the cell count, gram-stained smear and culture, acid-fast
bacilli stain and culture, cytologic studies, and chemistry testing. Malignant
ascites is typically exudative with a low albumen gradient. Cytologic
demonstration of tumor cells in ascitic fluid is also diagnostic.
False-positive results may occur because reactive mesothelial cells can
simulate carcinoma. Immunohistochemistry can also establish the
diagnosis. CT scanning and magnetic resonance imaging may show mesenteric
thickening, peritoneal studding, a tumor mass, and ascites, though advanced
disease may present without radiologic evidence. When the diagnosis remains
unclear, peritoneoscopy by laparoscopy permits visualization of
peritoneal deposits, cytologic assessment, and/or biopsy.
There is no staging system for primary peritoneal mesothelioma, though one has been proposed. The expected median survival time for peritoneal carcinomatosis is 1 to 2 years. Local invasion of the liver, abdominal wall, diaphragm, retroperitoneum, gastrointestinal tract, and bladder commonly occurs. Treatment involves a multidisciplinary approach, combining cytoreductive surgery, chemotherapy, hyperthermic perioperative intraperitoneal therapy, and irradiation. Surgical intervention can be palliative for debulking, particularly when intestinal obstruction is present.
