OVERVIEW
• The Arias-Stella reaction is a benign endometrial change due to hormonal effect. It was first described by Dr. Javier Arias-Stella in 1954. Also referred to as Arias Stella change
• It may be seen in pregnancy and postpartum
• It is characterized by hypertrophy and vacuolization of the cells of the endometrium, associated with marked nuclear pleomorphism, enlargement, and hyperchromasia.
• When it occurs in extra-uterine sites such as ovary, fallopian tubes, vagina and cervix, the differentiation of Arias-Stella changes from clear cell cancers in these locations can be challenging and the biopsy should be carefully examined to avoid misdiagnosis of cancer

ETIOLOGY
• Pregnancy associated
• Oral contraceptive use especially progesterone
• Trophoblastic disease associated

CLINICAL FEATURES
Incidental finding
May present as endocervical polyp when it occurs in the cervix

HISTOLOGICAL TYPES
Five histologic variants are recognized
• Minimal atypia – nuclear enlargement is minimal and occurs focally; usually at the start of pregnancy
• Early secretory pattern – Similar to normal early secretory endometrium with subnuclear or subnuclear / supranuclear vacuolation
• Secretory or hypersecretory pattern – Most common pattern; glandular cells with extensive cytoplasmic vacuolization; enlarged and hyperchromatic nuclei
• Regenerative, proliferative or nonsecretory pattern – Minimal evidence of secretory activity; enlarged vesicular nuclei
• Monstrous cell pattern – Usually occurs focally, with giant and bizarre nuclei, affecting all the glandular epithelial cells

DIFFERENTIAL DIAGNOSIS
• Clear cell adenocarcinoma
• Serous papillary carcinoma
• HPV associated endocervical adenocarcinoma
• Radiation or chemotherapy induced changes

SIGNIFICANCE OF ARIAS STELLA REACTION
Recognition of Arias-Stella reaction in extra-uterine locations, especially in young women, is important and to avoid a wrong diagnosis of clear cell adenocarcinoma. It is necessary to pay attention to cellular and nuclear detail and interpret the changes in the clinical context (pregnancy or other forms of hormonal stimulation).

MANAGEMENT
Arias Stella changes disappear after pregnancy.