Cystic Endometrial Hyperplasia in a Domestic Rabbit (Oryctolagus cuniculus domesticus)

Background: Cystic endometrial hyperplasia is a hormone-dependent disease induced by systemic increase in progesterone that can occur in several domestic species, such as the rabbit. This disease may be associated with sex steroid hormones, especially progesterone, and may be asymptomatic, and it is diagnosed using complementary imaging tests such as total abdominal ultrasound. However, surgical excisional biopsy with histopathological tissue analysis is the gold standard. This study reports a case of asymptomatic cystic endometrial hyperplasia in a female Miniature Lion Lop rabbit (Oryctolagus cuniculus domesticus) treated with therapeutic ovariohysterectomy. Case: A domestic, adult, female Miniature Lion Lop rabbit (Oryctolagus cuniculus domesticus), aged approximately 5 years and weighing 3.2 kg, was referred to specialized care to undergo ovariohysterectomy, an elective procedure. The tutor only reported the occurrence of a single episode of vulvar secretion more than 2 years ago, treated with antibiotics, with remission of clinical signs. In the intraoperative period after celiotomy, the uterine horn and uterine body showed a significant increase in volume, with abnormal color changes and tissue consistency; however, both changes were clinically asymptomatic. Subsequently, biopsy was performed during the ovariohysterectomy procedure. The excised uterus and ovaries were placed in 10% formalin and histopathologically analyzed. The macroscopic histopathological examination of the sectioned tissue revealed a slight amount of brownish fluid inside the uterine horns, in addition to multiple cystic areas in the uterine mucosa. Microscopic examination revealed marked hyperplasia of well-differentiated endometrial epithelial cells, occasionally forming cystic structures of different sizes. Moderate congestion, mild multifocal hemorrhage, and mild multifocal inflammatory infiltrate in the lamina comprising lymphocytes and plasma cells were also observed. Therefore, a diagnosis of cystic endometrial hyperplasia with mild lymphoplasmacytic endometritis was made. Observation of the patient was recommended without therapeutic indication. Discussion: Although the pathogenesis of cystic endometrial hyperplasia remains unknown, it is suggested that it is associated with the presence of sex steroids. Hence, this is a common disease in female rabbits, as they have non-seasonal polyestrous cycles and induced ovulation. Cystic endometrial hyperplasia may be asymptomatic or subclinical, without any significant clinical signs. Conversely, when associated with an infection such as pyometritis, the clinical signs include intermittent hematuria, anemia, lethargy, anorexia, and tenderness in the uterus on palpation. Although diagnosis can be made using total abdominal ultrasound and radiography, it can only be confirmed by the histopathological evaluation of the biopsied uterine tissue. Histopathological features of this disease include endometrial thickening with irregular glandular cystic elevations and hyperplasia of the pseudostratified cylindrical ciliated cells of the uterine glands. Furthermore, lymphoplasmacytic infiltrate is found in the uterine tissue, demonstrating an inflammatory reaction or bacterial infection concomitant with endometrial hyperplasia. In this case, the treatment of choice was therapeutic ovariohysterectomy, which is considered curative in this disease. Thus, ovariohysterectomy can resolve cystic endometrial hyperplasia in a domestic female Miniature Lion Lop rabbit.