Primary peritoneal epithelioid mesothelioma

Case contributed by Jan Frank Gerstenmaier


Incidental finding on chest radiograph during AVR workup.

Patient Data

Age: 75 years
Gender: Male

Pre-operative chest radiographs


PA and lateral erect views have been obtained. Previous imaging provided for comparison.

New mass like opacity right costophrenic angle, as well as nodular outline of right diaphragm.

The lungs and pleural spaces are clear. The cardiomediastinal contours are within normal limits. Small right diaphragmatic eventration noted.

CT chest and abdomen


CT preop demonstrates a right lower chest mass ? pleural/extrapleural.
CT abdo/pelvis to further characterize:

Soft tissue density material (~50 HU) distributed diffusely throughout the peritoneal cavity. It involves the right and left subphrenic spaces, extends under the spleen and liver, involves the left paracolic gutter and extends into the pelvis (large mass in the rectovesical pouch). It enters the porta hepatis extending along the posterior wall of the gallbladder and along the falciform ligament. There is scalloping of the liver and spleen. There is displacement of bowel loops. The soft tissue density extending up into the right hemithorax is again visualized. No evidence of bowel obstruction. Small left renal cyst (4 HU). The pancreas and adrenal glands are normal. No free intraperitoneal gas. Small right effusion. The lung bases are clear.

Diffuse low attenuation masses throughout the peritoneal cavity are consistent with extensive peritoneal metastasis. No obvious intra-abdominal primary tumor. US guided biopsy of the omental tumor is a better alternative to CT guided biopsy if required.

Ultrasound and biopsy


Diagnostic US demonstrates large masses seen on recent CT: at right lung base (largest dimension measuring up to 6 cm), and in left upper quadrant at splenic flexure (measuring 12 x 8 x 6 cm). Decision is made to biopsy the left abdominal mass.

Patient is prepped and draped. Sedation with 25 mcg fentanyl and 1 mg midazolam IV. 10 mL 1% lignocaine in subcutaneous soft tissues and at peritoneum. 2 x 18 G cores of mass taken under US guidance.

Microscopic description: The sections show features of malignant epithelioid tumor. The tumor forms trabeculae, nests with occasional acinar structures, surrounded by inflamed stroma. The tumor cells have enlarged nuclei, prominent nucleoli and moderate amounts of cytoplasm. Lymphovascular invasion is not seen. The tumor cells are CK7 positive. They are TTF-1, CK20, CDX-2 and PSA negative. This immunoprofile is non-specific. Possible primary sites include lung, upper gastrointestinal tract, biliary tract and pancreas.

Diagnosis: Omental mass biopsy: Metastatic poorly differentiated adenocarcinoma.

Supplementary report: Further immunostains have been performed after discussion at the MDM. The tumor cells are calretinin, CK5/6, mesothelin and WT1 positive (all mesothelial markers). They are BER-EP4 (adenocarcinoma marker) negative. The features are those of epithelioid mesothelioma.

Amended diagnosis: Omental mass biopsy: Epithelioid mesothelioma.

Case Discussion

The differentiation between adenocarcinoma and mesothelioma can be difficult at histology. In this case, the initial histological diagnosis of metastatic adenocarcinoma was revised following review of clinical and radiologal features, and the correct diagnosis was confirmed with special stains (calretinin, CK5/6, mesothelin and WT1) which are expressed in the majority of malignant mesotheliomas,

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