Abdominal Mesothelioma

Michael P. Federle, MD, FACR

Key Facts

Terminology

Rare primary malignant neoplasm arising from peritoneum

Imaging

70% of malignant mesotheliomas arise in pleura
- 20-30% of malignant mesotheliomas arise in peritoneum
- May also arise in pericardium, tunica vaginalis
Calcified pleural plaques in 50% of patients with peritoneal mesotheliomas
Omental and peritoneal-based masses
Stellate, thickened (“pleated”) mesentery secondary to encasement and straightening of mesenteric vessels
Spreads along serosal surfaces and directly invades adjacent viscera, especially colon and liver
Variable amount of ascites; massive ascites uncommon

Top Differential Diagnoses

Peritoneal metastases and lymphoma
- Cannot be distinguished from mesothelioma by imaging
- Is much more common than mesothelioma
Pseudomyxoma peritonei
Peritoneal inclusion cyst
- Sometimes (incorrectly) called “benign cystic (or multicystic) mesothelioma”
- Has nothing in common with malignant mesothelioma
Tuberculosis, abdominal manifestations

Pathology

Associated with asbestos exposure
- 20-40 year latency between exposure and diagnosis

(Left) Axial CT in an elderly man with abdominal distention shows a calcified pleural asbestos plaque

. The parietal peritoneum under the diaphragm is diffusely thickened

. (Right) Axial CECT in the same patient shows an omental mass

, loculated ascites, and a “stiff” mesentery (better shown on other sections). 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 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

along the peritoneal surface. Surgical biopsy confirmed malignant mesothelioma. This isolated mass is an unusual manifestation of the disease, which is usually widespread at the time of diagnosis.

TERMINOLOGY

Abbreviations

Malignant mesothelioma (MM), peritoneal mesothelioma (PM)

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 cake associated with calcified pleural plaques
Location
- 70% of malignant mesotheliomas arise in pleura
- 20-30% of malignant mesotheliomas arise in peritoneum
  - Few involve both pleura and peritoneum
- May also arise in pericardium, tunica vaginalis
Size
- Usually involves peritoneal surfaces diffusely or multifocally
- Focal masses from few mm to many cm
Morphology
- 2 primary forms
  - Desmoplastic form: Diffuse disease thickening peritoneal surfaces and enveloping viscera
  - Focal form: Large tumor mass with scattered satellite peritoneal nodules