Gliomatosis peritonei as a natural experiment in tissue differentiation.

Gliomatosis peritonei (GP) is an unusual condition in which nodules of mature astroglia, often miliary and microscopic in size, are widespread in the peritoneum and abdominal lymph nodes. Its behaviour is benign and it is usually found in association with ovarian teratoma and rarely with teratomas of other organs. Implants grow rapidly and can remain unchanged for life. Astroglia is the main component, but other neural lineage elements and many other tissues can be found. Cells are mature but not terminal, since they express SOX2. Secondary associated lesions include: a) degenerative astrocytic changes, b) granulomatous and follicular chronic inflammatory changes, c) association with hormonally related changes, such as decidual peritoneal metaplasia and endometriosis and d) endothelial and adventitial vascular hyperplasia leading to haemoperitoneum.Two pathogenetic mechanisms are considered: direct seeding of immature neural cells from a primary tumour with subsequent differentiation and metaplasia from peritoneal stem cells. The former proposal is supported by clinicopathologic data such as ample cellular heterogeneity, coexistence of mature astroglia with neural blastema, as well as the shed keratin and hairs from the ovarian neoplasm. However, metaplasia is sustained by a heterozygosity pattern of GP nodules, identical to the normal tissue and different from the coexistent ovarian teratoma. GP would constitute a response to growth factors from teratoma or macrophages. While an implantative origin from ovarian teratoma remains in most cases a more probable mechanism, metaplasia from peritoneal stem cells would explain cases of GP which present a monomorphic astrocytic cell population.