Adenomyosis (Endometriosis) in Bats
American Association of Zoo Veterinarians Conference 2007
Drury R. Reavill, DVM, DABVP (Avian Practice), DACVP; Robert E Schmidt, DVM, PhD, DACVP; Dawn Zimmerman, DVM, MS; Mike Douglass, DVM
Zoo/Exotic Pathology Service, Greenview, CA, USA


Adenomyosis is defined as the occurrence of endometrial tissue in the wall of the uterus, while endometriosis indicates endometrial glands or stroma outside the uterus. In animals these conditions occur only in those species that menstruate, and have been well documented in nonhuman primates, dogs, cats and cattle. This paper presents the occurrence of adenomyosis (endometriosis) in a group of eight short-tailed bats (Carollia perspicillata).

In all cases the bats were presented dead with no premonitory signs. The uterus was variably enlarged, with thickened endometrium. Blood was seen in the lumen and in some cases coming from the vulva. Many of the animals had yellow-brown material in the lumen. Histologically the uterine lesion was infiltrative and comprised of variably sized tubular structures arranged in small clusters. These structures were lined by cuboidal to attenuated epithelial cells with scant to small amounts of granular eosinophilic cytoplasm and round nucleus. The nucleus had stippled chromatin and one or multiple nucleoli. Larger tubular structures contained intracytoplasmic granular eosinophilic material. These structures extended from the endometrial mucosa and penetrated through the submucosa in multiple places but did not penetrate through the myometrium. Few mitoses were seen. There was a mild scirrhous tissue reaction.

Adenomyosis in humans may be asymptomatic or associated with clinical signs including abnormal bleeding and uterine enlargement. It indicates downgrowth of endometrial tissue into the myometrium. Hemorrhage can occur within the small endometrial downgrowths. In animals the cause has been considered to be prolonged estrogen stimulation, and focal or diffuse swelling of the uterus is the most commonly reported sign. The abnormal endometrial glands may become distended with purulent material. Endometriosis is the presence of functional endometrial tissue outside the uterus. The cause of endometriosis is not known for certain. Theories of its pathogenesis include retrograde menstruation through the fallopian tubes with subsequent implantation of endometrial cells in abnormal locations, metaplasia of coelomic epithelium, and vascular or lymphatic dissemination via pelvic veins or lymphatics associated with an immune system defect.

Although morphologically typical endometriosis was not seen in these bats, its occurrence is possible. Like primates, short-tailed fruit bats have a simplex uterus and true menstruation.1,2 This could also possibly explain why the adenomyosis in these animals appears to have been more severe than that described in domestic animals. The cause of the lesions is also not known. In humans a genetic predisposition for endometriosis has been documented, and the same may be true in animals.

Literature Cited

1.  Rasweiler JJ IV, deBonilla H. Menstruation in short-tailed fruit bats (Carollia spp.). J Reprod Fert. 1992;95:231–248.

2.  Oliveira SF, Rasweiler JJ IV, Badwaik NK. Advanced oviductal development, transport to the preferred implantation site, and attachment of the blastocyst in captive-bred, short-tailed fruit bats, Carollia perspicillata. Anat Embryol. 2000;201:357–381.


Speaker Information
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Robert E. Schmidt, DVM, PhD, DACVP
Zoo/Exotic Pathology Service
Greenview, CA, USA

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