Glands with serrated lumens lined by plump vacuolated epithelial cells. The tortuous glands resemble endometrial glands in late secretory phase.

Cytoarchitectural changes include intraluminal budding, nuclear enlargement and hyperchromasia, cytoplasmic swelling and vacuolation. Some cells with enlarged nuclei and scant cytoplasm can protrude into the lumen, creating a hobnail appearance.

The glands somewhat resemble secretory endometrium, with focal back to back architecture and infoldings into the lumen .

Most of the cells show cytoplasmic budding into the lumen, along with a few enlarged nuclei.

Another area again shows scattered enlargement of the nuclei, but without hyperchromasia. Pronounced budding of cells with clear cytoplasm can be seen. Vacuolization of the cytoplasm is usually prominent.

Confluent stromal decidualization is seen, along with a gland lined by cells with variably sized nuclei.

Nuclear atypia can be disconcerting but unlike clear cell carcinoma, the chromatin is smooth and uniform. Optically clear nuclei, several of which are seen here, are often encountered in Arias-Stella. The lumen contains some mucinous material.

The Arias-Stella reaction typically occurs in endometrial and endocervical glands in response to pregnancy. Note that the presence of Arias-Stella reaction in an endometrial biopsy does not confirm the presence of an intrauterine pregnancy, as an ectopic pregnancy and gestational trophoblastic disease can also lead to the same changes.1

The main entity to distinguish from Arias-Stella reaction is clear cell carcinoma. Arias-Stella ought to be associated with other changes of pregnancy such as hypersecretory glands and decidua. Clear cell carcinoma forms a mass lesion, elicits a desmoplastic stromal response and has an infiltrative pattern with frequent mitotic figures, features not seen in Arias-Stella.2

→Key histologic features include a tortuous glandular architecture reminiscent of secretory endometrium, nuclear enlargement and hyperchromasia, cytoplasmic vacuolization and hobnailing.

→Unlike clear cell carcinoma, the chromatin is smooth and bland, there is no desmoplastic reaction and stroma decidualization ought to be present.

• Fallopian Tube : Decidualization

• Cervix : Clear Cell (Adeno)carcinoma

• Ovary : Clear Cell Carcinoma