Arias-Stella reaction

The Arias-Stella reaction is a benign change.

General

• Benign atypical endometrial changes associated with chorionic tissue.
  • May be seen in a normal pregnancy, hydatidiform moles, others.
• Historically it was diagnosed as endometrial cancer.
• Usually in premenopausal women - pregnant or recently pregnant; however, it may be seen postmenopausal women.

Note:

• To the novice... the nuclei look really scary, i.e. they look like cancer.

Microscopic

Features:

• Epithelial component of endometrium with large nuclei - key feature.
  • +/-Nuclear hyperchromasia, i.e. dark nuclei.
  • +/-Irregular nuclear membrane.
  • +/-Nuclear clearing.
  • +/-Nuclear pseudoinclusions.
• NC ratio is preserved.
• Usually a focal change.
• +/-Mitoses - uncommon.

Notes:

• No decidual reaction in the stroma.

DDx:

• Choriocarcinoma.
• Herpetic endometritis.
• Clear cell endometrial carcinoma.
• Serous endometrial carcinoma.

Images:

• Intermediate trophoblast reaction - low mag. (WC).
• Intermediate trophoblast - high mag. (WC).

Subtypes

There are five subtypes:

1. Minimal atypia.
   • Usually early gestation.
2. Early secretory pattern.
   • Mimics secretory endometrium: cytoplasmic vacuoles, central nucleus, palisading architecture.
3. Secretory or hypersecretory pattern.
4. Regenerative, proliferative or nonsecretory pattern.
5. Monstrous cell pattern.

See also

• Gynecologic pathology.