20-30% of malignant mesotheliomas arise in peritoneum
• CT: Omental and peritoneal stranding, nodularity, and discrete masses
Stellate, thickened (pleated) mesentery secondary to encasement and straightening of mesenteric vessels
Tumor spreads along serosal surfaces and can directly invade adjacent viscera, especially colon and liver
Can spread across diaphragm into pleural cavity
Less ascites than peritoneal carcinomatosis
Calcified pleural plaques may be clue to diagnosis
• MR: Low to intermediate T1WI and intermediate to high T2WI signal intensity of omental and peritoneal masses
• Typically no distant metastatic disease or lymphadenopathy
TOP DIFFERENTIAL DIAGNOSES
• Peritoneal carcinomatosis
• Lymphomatosis
• Pseudomyxoma peritonei
• Tuberculous peritonitis
• Sclerosing mesenteritis
PATHOLOGY
• Relationship with asbestos exposure is less strong than with pleural mesothelioma (requires much higher exposure to asbestos than pleural mesothelioma)
Asbestos is still strongest risk factor
CLINICAL ISSUES
• Rare tumor (1-2 cases per million) with extremely poor prognosis (most patients die within 1 year)
• M:F > 4:1; usually 6th-7th decade
• Treatment: Cytoreductive surgery and peritonectomy combined with heated intraperitoneal chemotherapy
(Left) Axial CECT in an elderly man with abdominal distention shows a calcified pleural asbestos plaque . The parietal peritoneum under the diaphragm is diffusely thickened with a discrete mass .
(Right) Axial CECT in the same patient shows an omental mass with loculated ascites. The abdominal findings are indistinguishable from peritoneal carcinomatosis, but the asbestos plaque is an important clue to the diagnosis of mesothelioma.
(Left) Axial CECT in an elderly man with abdominal pain shows marked mass-like omental thickening and encasement of bowel loops . Open biopsy confirmed malignant mesothelioma.
(Right) Axial NECT in a patient with renal insufficiency shows a lobulated mass in the omentum abutting the anterior abdominal wall. Surgical biopsy confirmed malignant mesothelioma. Such an isolated mass is an unusual manifestation of the disease, which is usually widespread at the time of diagnosis.
TERMINOLOGY
Abbreviations
•
Synonyms
• Malignant mesothelioma, peritoneal mesothelioma
Definitions
• Primary malignant neoplasm arising from peritoneum
• “Benign cystic mesothelioma” is misnomer
More accurately referred to as “peritoneal inclusion cyst”
Has nothing in common with malignant mesothelioma other than having mesothelial cells in its lining
IMAGING
General Features
• Best diagnostic clue
Peritoneal masses or omental caking associated with calcified pleural plaques
• Location
Malignant mesothelioma can arise from pleura, peritoneum, pericardium, tunica vaginalis, or any other serosal membrane in body
– 70% of malignant mesotheliomas arise in pleura
– 20-30% arise in peritoneum
– Very few cases involve both pleura and peritoneum
• Size
Usually involves peritoneal surfaces diffusely or multifocally
– Localized (focal): Large tumor mass with scattered satellite peritoneal nodules
Radiographic Findings
• Radiography
Calcified pleural plaques in 50% of patients with peritoneal mesotheliomas
– Only 20% of pleural mesotheliomas have calcified plaques
– Suggests heavier asbestos exposure in patients with peritoneal mesothelioma
Fluoroscopic Findings
• Separation and fixation of bowel loops
• Spiculation of loops when bowel wall invaded
• Segmental stenoses with circumferential bowel invasion
CT Findings
• Omental and peritoneal stranding, nodularity, and discrete masses
Stellate, thickened (pleated) mesentery secondary to encasement and straightening of mesenteric vessels
Spreads along serosal surfaces and can directly invade adjacent viscera, especially colon and liver
Can spread across diaphragm into pleural cavity
Calcification in peritoneal masses is very uncommon
• 2 primary forms
Diffuse (desmoplastic) peritoneal mesothelioma: Diffuse thickening of peritoneal surfaces and omentum with involvement of entire abdomen and multiple discrete masses
– Aggressive form that accounts for majority of cases
Localized (focal) peritoneal mesothelioma: Solid dominant mass in 1 portion of abdomen without widespread disease or nodularity
– Mass may infiltrate and involve adjacent local organs, but does not spread to distant sites in abdomen
– Lesser degree of ascites
– May have better prognosis, but only represents a minority of cases
• Variable amount of ascites: Massive ascites uncommon
Amount of ascites in mesothelioma (for a given amount of solid tumor burden) tends to be less than is seen with peritoneal carcinomatosis
• Calcified pleural plaques may be clue to diagnosis
• Does not typically demonstrate distant metastatic disease or lymphadenopathy
Buy Membership for Radiology Category to continue reading. Learn more here
Stellate, thickened (pleated) mesentery secondary to encasement and straightening of mesenteric vessels
. The parietal peritoneum under the diaphragm is diffusely thickened 
with a discrete mass 
.
with loculated ascites. The abdominal findings are indistinguishable from peritoneal carcinomatosis, but the asbestos plaque is an important clue to the diagnosis of mesothelioma.
and encasement of bowel loops 
. Open biopsy confirmed malignant mesothelioma.
in the omentum abutting the anterior abdominal wall. Surgical biopsy confirmed malignant mesothelioma. Such an isolated mass is an unusual manifestation of the disease, which is usually widespread at the time of diagnosis.
Diffuse (desmoplastic) peritoneal mesothelioma: Diffuse thickening of peritoneal surfaces and omentum with involvement of entire abdomen and multiple discrete masses
