Use of reticulin stain in the diagnosis of intra-uterine gestation

Summary Aims The diagnosis of intra-uterine gestation may be problematic when specimens from clinically suspected products of conception lack chorionic villi and/or fetal somatic tissues, since the distinction of intermediate trophoblast from decidual or myometrial elements can be difficult. The placental site is also characterised by stromal changes, including the deposition of a characteristic extracellular fibrinoid matrix. We have noted that these stromal changes may be highlighted by a simple reticulin stain; therefore, we have evaluated reticulin staining in a series of endometrial biopsy specimens from patients with intra-uterine and ectopic gestations. Methods Reticulin staining was performed in 28 endometrial specimens from patients with first trimester intra-uterine gestations, including 14 cases that lacked chorionic elements. Eight endometrial samples from patients with concurrent histologically verified tubal ectopic pregnancy were also examined. Selected cases were also studied using a Masson trichrome stain, and immunohistochemically with antisera to cytokeratin and HPL. Results There was a distinct increase in reticulin staining, usually evident at low power magnification, in most areas of decidua showing implantation site. Prominent reticulin staining was present around the decidual and trophoblast cells and there was also accentuation around stromal vessels, glands and myometrial cells. There was no clear difference in staining within areas of decidua including only rare intermediate trophoblast cells but this pattern was seldom seen in isolation. Minimal changes were seen in the placental site using the Masson trichrome stain. Conclusions Reticulin stains may prove useful in the assessment of endometrial specimens from patients with purported intra-uterine gestations when chorionic elements are not identified. Since the staining technique is simple and can be quickly performed, it could be used as an adjunct to conventional H&E assessment and to select appropriate specimen blocks for additional more sensitive studies, including immunohistochemistry