Primary neoplasia of the female peritoneum.

Primary neoplasms of the female peritoneum may be mesothelial or Müllerian in nature. Primary mesotheliomas may be cystic, benign papillary or diffuse malignant. Primary Müllerian tumours of the peritoneum are thought to arise within the secondary Müllerian system: the overwhelming majority are serous in nature and probably develop from pre-existing endosalpingiosis. Primary peritoneal serous tumours of borderline malignancy are identical histologically to the peritoneal 'implants' found in association with ovarian serous tumours of borderline malignancy, whereas primary peritoneal serous adenocarcinomas are histologically identical to ovarian serous adenocarcinomas. The recognition of a primary peritoneal serous neoplasm of borderline malignancy rests on the presence of either normal ovaries, ovaries containing only a fully benign neoplasm or ovaries showing only minimal surface involvement. The diagnosis of a primary peritoneal serous adenocarcinoma is made if the ovaries are of normal size with either no tumour or only minimal surface involvement: in some cases normal ovaries will have previously been prophylactically removed because of a family history of ovarian cancer. The differential diagnosis between a primary serous adenocarcinoma and a diffuse malignant mesothelioma can be difficult and is often not resolved by either electronmicroscopy or immunocytochemistry.