Cystic endometrial hyperplasia (CEH) is a common uterine disorder in older intact female dogs, being characterized by an abnormal cystic distension of the endometrial glands [[1], [2], [3]]. Although its exact cause is still unknown, it has been suggested that CEH may occur in response to repeated stimulation of the uterus by progesterone in older female dogs [4,5].

Poor conception rates and low litter sizes have been reported in bitches affected by CEH [6,7]. It has been suggested that these phenomena are likely attributable to post-mating endometritis, which is characterized by a reduced uterine vasodilatory response to mating as well as impaired clearance of uterine fluid due to decreased uterine contractility compared with normal bitches [6]. A larger polymorphonuclear neutrophils influx has been observed in bitches with CEH post-mating which could affect the ability of spermatozoa to attach to the uterine epithelium with direct impacts on fertility [7]. Additionally, a recent study reported a decrease in normal preantral follicle and ovarian stromal cell densities in dogs affected by CEH and pyometra compared with normal dogs, suggesting that an inappropriate uterine environment may lead to premature depletion of ovarian reserve and impaired fertility potential [8]. Furthermore, CEH may have a negative impact on the placentation process, particularly by disturbing implantation, foetal development and viability. [9]. In addition to the impact on fertility, changes in the endometrium may lead to further infections and favour the development of pyometra. [3,10]. In fact, even if the true relationship between the two conditions is not yet known, pyometra and CEH can coexist, resulting in a condition often referred to as the ‘CEH-pyometra complex’ [10,11].

Even if the prevalence of CEH is still debated today [3,12], there is evidence that breed [13] and increasing age [3] may be risk factors.

B-mode ultrasound is widely recognised as the preferred method for evaluating the uterus in dogs, enabling the assessment of uterine changes during the different phases of the oestrus cycle [14] and the detection of uterine disorders [3,15]. In dogs affected by CEH, uterine layers integrity is affected by the presence of cysts [15,16]. The size and amount of the cysts may be highly variable, and this may limit the capability of the operators to assess the severity of the condition. Bigliardi and colleagues tried to correlate the ultrasound findings with histological classifications in dogs with CEH-pyometra complex [17]. However, to the best of our knowledge, there is no widely recognised standardized method of characterising CEH in dogs using ultrasound, meaning that the disease is generally described and evaluated subjectively. It has been shown that lack of standardization for imaging documentation can potentially lead to inaccuracies, while standardized reporting systems reduce errors and variations in healthcare [18]. The present study aims to establish an objective and standardized ultrasonographic method to score CEH features and grade the disease in female dogs, providing new insights into ultrasonographic pathological appearance of the uterus in bitches.

We hypothesize that the development of an ultrasonographic grading system for CEH could represent a valuable diagnostic and documentation tool. It may improve inter-observer agreement, favour a better documentation of disease progression or regression in individual dogs and may potentially help to better predict fertility or disease risks.