Atrophic quiescent glands are embedded in a spindled stroma.
Small tubular glands are surrounded by a spindled and mildly edematous stroma. In certain forms of 'pill endometrium' the stroma may be predecidualized. However, when a woman ingests low-dose OCP or after long-term usage, the stroma becomes atrophic.
The glands only hint at secretory activity as seen by apical snouts.
This patient shows long term use of the pill but also small foci of breakdown along the surface. Other areas shows microthrombi.
Pill effect or 'pill endometirum' occurs when a woman takes a combination oral contraceptive pill containing progestin and estrogen. The effect of progestin dominates and note that there is a spectrum of changes depending on how long the woman has been taking the pill.
Initially, progestins will induce secretory differentiation and there will be a mixture of proliferative and secretory features. Predecidual change is not prominent until after a few cycles. After several cycles, the glands develop secretory exhaustion and become quiescent and atrophic. At this point, the stromal is well-developed and predecidualized. The histologic picture of atrophic glands against a background of predecidualized stroma is what some experts (Robboy) call the 'classic pill endometrium'.1
Eventually, the stroma loses sensitivity to hormonal stimulation and no longer exhibits precidualization. Both glands and stroma are atrophic. Remember that progestins downregulate estrogen and progesterone receptors and so that long-term exposure will blunt endometrial response to these hormones.
Often, especially in low dose regimens, the stroma may not exhibit precidualization. In fact, small tubular glands in a background of edematous and spindled stroma is what Dr. Crum defines as 'pill endometrium' in his text.2
1 Robboy SJ, Anderson MC, Russell P. Pathology of the Female Reproductive Tract. London, UK: Churchill Livingstone; 2002: 268-271
2 Crum CP, Lee KR. Diagnostic Gynecologic and Obstetric Pathology. Philadelphia, PA: Elsevier; 2006: 472-5.