Endometrial polyps in 2 African pygmy hedgehogs

Abstract

Reports of spontaneously occurring endometrial polyps in animals are rare and have only involved a few species. This report is intended to advise veterinarians that older African pygmy hedgehogs may develop endometrial polyps and that these lesions can be a cause of bloody vaginal discharge, sometimes interpreted as hematuria.

Case descriptions

A 6-year-old, female, African pygmy hedgehog (Atelerix albiventris) had been passing blood in its urine for 1 to 2 mo. A thorough urinalysis could not be performed. Radiographs did not reveal any urinary tract calculi, although there was an area of increased radiodensity in the lower abdomen. An exploratory laparotomy revealed an enlarged uterus, an ovariohysterectomy was performed. The ovaries and uterus were placed in 10% neutral buffered formalin and submitted to the veterinary diagnostic laboratory at the Western College of Veterinary Medicine (WCVM). The animal recovered uneventfully, but died several months later. A postmortem examination was not performed.

A 2nd female African pygmy hedgehog, also 6 y of age, was anorexic, weak, and passing blood in its urine. Examination of the peripheral blood revealed a hematocrit of 0.22 L/L (reference range, 0.22 to 0.64 L/L [1]), marked polychromasia, 130 nucleated erythrocytes per 100 leukocytes, and a leuckocytosis (104 × 10⁹/L; reference range, 3 to 43 × 10⁹/L [1]). After considering the costs associated with additional tests needed to arrive at a more specific diagnosis and for treatment, as well as the advanced age of the animal, the owners opted to have the animal euthanized. The carcass was frozen and submitted to the veterinary diagnostic laboratory at the WCVM for necropsy.

In the 1st case, a single, slightly curved, dark, soft tissue mass, 2.25 cm long by 0.5 cm diameter, was present in the lumen of the uterus, attached to the endometrium by a thin stalk (Figure 1). In the 2nd case, the uterus, particularly the distal aspect of the left horn and the proximal aspect of the right horn, was moderately enlarged and the serosa reddened (Figure 2). Within the uterus at these 2 locations, curved, dark red, soft tissue masses, approximately 1.5 cm long by 0.5 diameter, were attached to the endometrium by a thin stalk (Figure 3). The urinary bladder and other viscera were normal.

Figure 1.

The formalin-fixed uterus from a 6-year-old African pygmy hedgehog. The uterus has been incised to reveal a 2.25 cm long by 0.5 cm diameter, dark, soft tissue mass (long arrow) that was present in the lumen and attached to the endometrium by a thin stalk (short arrow).

Figure 2.

The uterus and urinary bladder from a 6-year-old African pygmy hedgehog. The distal aspect of the left horn and the proximal aspect of the right horn are moderately enlarged and reddened. Legend: a — left horn; b — right horn; c — body; d — urinary bladder.

Figure 3.

The same uterus as pictured in Figure 2. Much of the uterine wall has been removed to reveal 2, approximately 1.5 cm long by 0.5 diameter, curved, dark red, soft tissue masses (long arrows), each attached to the endometrium by a thin stalk (short arrows).

Histologically, the masses were mostly necrotic and composed principally of well vascularized fibrous tissue (Figure 4). Within each mass, there was extensive to diffuse hemorrhage and several blood vessels appeared to be plugged with fibrin (thrombosed). At the base of each mass, near the attachment of the stalk, spaces lined with epithelium were interpreted to be glandular structures. On the surface of the masses were multiple foci of fibrin and segments of cuboidal epithelium, similar to that lining the uterus. Based on the gross and histologic findings, a diagnosis of a single (case 1) and multiple (case 2) endometrial polyps was made. In both animals, the endometrium appeared thin with few glands, consistent with senile atrophy. However, there was clustering or nesting of glands (Figure 5); a few glands were composed of densely packed, columnar epithelial cells with increased basophilia (Figure 6), interpreted as hyperplasia; and several glands were dilated or cystic (Figures 5, 7).

Figure 4.

The histologic appearance of the mass (pictured in Figure 1) present in the lumen of the uterus of a 6-year-old African Pygmy Hedgehog. The blue staining fibers are collagen. Arrows point to necrotic glandular structures. Masson’s trichrome stain. Bar = 100 μm.

Figure 5.

Endometrial glands arranged in clusters or nests in the uterus (pictured in Figure 1) of a 6-year-old African pygmy hedgehog. Also note that several glands are dilated. Hematoxylin & eosin stain. Bar = 250 μm.

Figure 6.

Endometrial glands in the uterus (pictured in Figure 1) of a 6-year-old African pygmy hedgehog. The endometrial gland on the right is composed of densely packed, columnar epithelial cells with increased basophilia, interpreted as hyperplasia. The endometrial gland on the left is more typical in appearance of most of the endometrial glands. Hematoxylin & eosin stain. Bar = 50 μm.

Figure 7.

Dilated and cystic endometrial glands in the uterus (pictured in Figure 1) of a 6-year-old African pygmy hedgehog. Hematoxylin & eosin stain. Bar = 500 μm.

Discussion

A polyp is a ‘morbid excrescence’ or an abnormal projection or outgrowth; a mass of swollen and hypertrophied tissue protruding from a mucous membrane (2–4). Endometrial polyps, also referred to as uterine polyps, are benign growths that are uncommon spontaneous lesions in humans (5–7) and laboratory rats (8–12); have been reported rarely in laboratory mice (13), fat sand rats (14), hedgehogs (15,16), cats (17), dogs (17,18), horses (19–21), and elephants (22); and have not been reported in other species of animals. Endometrial polyps may not be associated with clinical signs. However, if a polyp becomes ulcerated or necrotic, it may be the source of hemorrhage. Endometrial polyps have also been associated with inversion and prolapse of the uterus in humans and dogs.

A unifying explanation for the development of all endometrial polyps does not exist. However, 2 factors appear associated with increased prevalence in humans: increasing age and tamoxifen therapy (5–7). Endometrial polyps appear to be most common in perimenopausal women (around age 50), and in women receiving tamoxifen as an adjuvant therapy for breast cancer. While tamoxifen has antiestrogenic effects on mammary tissue, it is thought to be an estrogen agonist in the endometrium and contribute to endometrial hyperplasia (5–7). It is thought that endometrial hyperplasia predisposes to polyp formation. In their study of endometrial polyps in dogs and cats, Gelberg and McEntee (17) found that most affected animals were mature, if not older (mean for animals of known age was 8.8 y for dogs and 9.4 y for cats), and most of the affected animals had cystic endometrial hyperplasia in adjacent areas of the uterus. Development of endometrial polyps also appears to be related to increasing age in laboratory mice (13), laboratory rats (8–12), fat sand rats (14), hedgehogs (15,16), and elephants (22), but not in horses. Horses diagnosed with endometrial polyps reported in the literature were between 1 and 2 y of age (19–21). Both hedgehogs discussed here were 6 y of age. Life expectancy of African pygmy hedgehogs is reported to be 4 to 6 y, and their reproductive life span is reported to be 2 to 3 y following sexual maturity at between 2 and 6 mo (1). Generally, the endometrium in these cases appeared quiescent, although there were a few hyperplastic glands, and several dilated and cystic glands in both. Whether these changes predispose to endometrial polyp development or are simply coincidental changes related to advancing age remains unknown.

These cases, combined with similar cases reported previously (15,16), serve to advise veterinarians, both clinicians and pathologists, that endometrial polyps occur in hedgehogs and may be a cause of bloody vaginal discharge, sometimes interpreted as hematuria.