The tubal stroma beneath the epithelium shows increased eosinophilic cytoplasm indicative of decidual change.
The decidualized cells are better visualized on higher power -- note their polygonal shape and abundant eosinophilic cytoplasm.
The fallopian tube stroma undergoes decidualization in 5-12% of intrauterine pregnancies and up to 80% of tubal pregnancies.1 Microscopically, one sees polygonal cells with abundant pink cytoplasm with prominent cell borders. The nuclei are uniform, bland and ovoid/round.
Seen most often in those undergoing tubal ligation after delivery and rarely, and in women receiving progestin therapy.
1 Nucci MR, Oliva Esther. Gynecologic Pathology: Foundations in Diagnostic Pathology. Philadelphia, PA: Elsevier: 2009: 331-2.