- In the initial stage the disease is characterized by numerous small nodules or plaques covering visceral and parietal serosal surfaces.

- At the later stage individual nodules fuse and form a diffuse, sheetlike thickening often encasing and compressing the lungs or the intestines and sometimes the liver and spleen.

- The final stage of the disease are marked by massive encasement of the viscera with matting of the affected structures, commonly causing complete obliteration of the pleural or peritoneal cavity. This may cause fatal functional disturbance.

In some cases tumour extends through the chest or abdominal wall along a needle biopsy tract or a scar from a previous excision. This complication should be kept in mind when planning thoracoscopy or needle biopsy or when aspirating fluid for cytological examination or relief of symptoms.

Macroscopically the tumour varies greatly in appearance and may be firm and rubbery or soft and gelatinous. Cut surface is greyish-white and  glistening in appearance. There may be foci of hemorrhage or necrosis.

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PLEURA: Parietal pleura is usually more extensively involved ;

Usually located in the inferior aspect of the cavity & diaphragm ;

Lung parenchyma may be involved in some cases ;

Distance metastases has been reported in about 50% cases.

PERITONEUM:  Variable growth pattern ; Indistinguishable from extensive carcinomatosis ; 

Multiple coalescing grey-white nodule in greater omentum and visceral peritoneum ;

Tumour is firm or hard in consistency ; Cystic and mucoid areas may be present  ;

Encasement of the intra-abdominal organs ;

Intramucosal tumour may present as multiple intestinal polyps ;

Liver and spleen may contain tumour nodules ;

Other mesothelial lesions may be present: - Well differentiated papillary mesothelioma ; multicystic mesothelioma; deciduoid mesothelioma ; adenomatoid tumour.

PERICARDIUM:  Not a common site for diffuse mesothelioma ;

Tumour may encase heart and great vessels.

TUNICA VAGINALIS TESTIS: Rare tumour presents as multiple nodules ;

Invade testicular parenchyma, spermatic cord and subcutaneous tissue of penis ; Hydrocele is usually present ;

D/D: Adenocarcinoma of rete testis , metastatic tumour from primary lung , renal and prostatic carcinomas.

Malignant peritoneal mesothelioma. J Surg Oncol. 2005;91(1) :17-25.

Extended surgical staging for potentially resectable malignant pleural mesothelioma.Ann Thorac Surg. 2005;80(6):1988-92; discussion 1992-3.

Pleural mesothelioma with cutaneous extension to chest wall scars.J Cutan Pathol. 2004 ;31(7):497-501.

Disseminated malignant solitary fibrous tumor of the pleura.Pathol Int. 2004 ;54 (2) :111-5.

Resection margins, extrapleural nodal status, and cell type determine postoperative long-term survival in trimodality therapy of malignant pleural mesothelioma: results in 183 patients.J Thorac Cardiovasc Surg. 1999 Jan;117(1):54-63; discussion 63-5

Diagnostic criteria for human diffuse malignant mesothelioma.Acta Pathol Jpn. 1992 Nov;42(11):767-86.