Adenomatoid tumor is a relatively uncommon, benign neoplasm of mesothelial origin that is usually confined to the male and female genital tracts (located in the myometrium, fallopian tube, ovary, epididymis, tunica albuginea, and testicular parenchyma).

Rare extragenital adenomatoid tumors have been identified in the adrenal glands, heart, mesentery, pleura, and lymph nodes.

Macroscopic features:  Two types of gross features have been described:  Small, solid tumours and large, cystic ones.   Image Link

Microscopic features: These tumours are composed of fibrous tissue, which are separated by numerous slit-like and pseudotubular spaces. The tumour may exhibit a variety of appearances (papillary, adenoid, tubular and solid patterns). In some cases marked cytoplasmic vacuolisation may produce  a signet ring cell appearance and mimic diffuse mesothelioma.

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The mesothelial origin of the adenomatoid tumor can be easily documented by such ancillary tests as immunohistochemical or electron microscopic studies.