Pseudo Placentational Endometrial Hyperplasia (PEH) in Female Dog

Abstract

Pseudo-placentational endometrial hyperplasia (PEH) is a distinct uterine lesion in dogs, exhibiting histological features that mimic normal placental structures. Initially reported by Krainz (1914) through the accidental discovery of organized endometrial responses to intrauterine porcelain balls, PEH has since been recognized as a progesterone-driven pathology most commonly occurring during diestrus. Subsequent experiments confirmed that foreign material inserted into the uterus during diestrus reliably induces deciduoma-like formations. Clinically and pathologically, PEH is distinguishable from cystic endometrial hyperplasia (CEH) by its organized, decidualized architecture. Recent studies have shown that PEH may also arise in the absence of pregnancy, often in cases involving pseudopregnancy, early embryonic resorption or failed implantation. Exogenous progestin administration and prolonged luteal phases are strongly implicated in the pathogenesis. Grossly, PEH presents with ovoid uterine swellings, thickened mucosa and villous protrusions that may occlude the lumen. Histologically, the endometrium demonstrates a three-layered structure: a deep glandular zone, a fibrous connective tissue band and luminal epithelial folds, without fetal tissue. Clinically, bitches may show signs of mucoid or hemorrhagic vaginal discharge, abdominal distension, lethargy and signs mimicking pseudopregnancy. Diagnosis is confirmed by combining clinical history, ultrasonography and definitive histopathology. Despite its distinct features, PEH remains underdiagnosed, often misidentified as CEH or pyometra, underscoring the need for improved recognition and differentiation among uterine pathologies.