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An Arias-Stella reaction is a common gynecological histological finding in curettage specimens of gestational endometrium describing a non-neoplastic lesion that is easily confused with uterine malignancy 1,2.
An Arias-Stella reaction is due to hormonal hyperstimulation causing atypical endometrial glandular cells associated with the presence of viable chorionic tissue 3.
It can present in normal physiologic conditions including pregnancy, postpartum and uterine abortion but is also associated with ectopic pregnancy, gestational trophoblastic disease, and uterine disease affecting the myometrium 1.
The reaction has also been found in extra-endometrial sites 4.
The characteristic features of the Arias-Stella reaction include hypertrophic and hyperchromatic nuclei with abundant cytoplasm and infrequent mitotic activity. The nuclei may protrude into the glandular lumen creating a hobnail appearance 5.
There are five histologic variants that are comparable with the phases of normal endometrium and the associated degree of atypical cells present 1:
minimal atypia: usually seen at the beginning of gestation with minimal hypertrophied nuclei and in limited numbers
early secretory pattern: resembles normal early secretory endometrium with glandular cells having a marked number of centrally located hypertrophied nuclei arranged in a palisading fashion with subnuclear or supranuclear vacuoles
secretory or hypersecretory pattern: hypertrophied glandular cells with a compact pyknotic hyperchromatic nuclei and a diffuse centronuclear cytoplasmic vacuolization 3
regenerative, proliferative, or nonsecretory pattern: hypertrophied glandular cells display a vesicular chromatin pattern with minimal secretory activity; usually found in cases of hydatidiform mole, choriocarcinoma and ectopic pregnancy 1
monstrous cell pattern: rare, all cells display a giant and bizarre nuclei with a dense homogeneous chromatin and frequent pseudoinclusions