Cystic endometrial hyperplasia, pseudo-placentational endometrial hyperplasia, and other cystic conditions of the canine and feline uterus
Introduction
Cysts arising from the wall of the canine uterus can be divided into those that involve the endometrium (by far the most common and clinically important) and those that arise within the myometrium or from the serosal surface of the uterus. Cysts that develop from the endometrium (generally referred to as cystic endometrial hyperplasia or CEH) vary greatly in size, number, distribution, histomorphology, and clinical relevance. Cystic endometrial hyperplasia is an important common lesion that can progress to pyometra [1], [2], [3]. The pathogenesis of endometrial hyperplasia, associated cyst development, and/or progression in some cases to pyometra has been of keen interest and has been the subject of many experimental [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29] and clinical studies. The latter have included assessment of methods for accurate clinical diagnosis [30], [31] and treatment response to various protocols [32], [33], [34], [35], [36]. A specific form of canine endometrial hyperplasia was first observed by researchers who, while conducting surgical experiments on canine uteri [37], [38], noted marked endometrial proliferative responses at the surgical sites. The pathogenesis of these lesions will be contrasted to those of the more common cystic changes of individual endometrial glands.
Many of the less common cysts found in the canine uterus are incidental findings, but these can be dramatic in appearance and can nearly always be diagnosed based on their location and other features.
The objectives of this paper are to review cystic conditions involving the uterus of the bitch, to present examples of the most common of these, and to discuss their pathogenesis and diagnosis.
Section snippets
Methods
The literature relating to the patho-physiology of cystic lesions in the bitch and queen was reviewed. Cases diagnosed with common cystic uterine lesions were identified from either the senior author's reproductive pathology archives or the files of the Section of Anatomic Pathology of the Animal Health Diagnostic Center at Cornell University. Glass slides that exemplified key morphologic features of the cystic uterine lesions were chosen. Demonstration of size, distribution, and many other
Cystic conditions of the endometrium
Endometrial cysts of the queen and bitch generally arise from endometrial glandular epithelium (Fig. 1, Fig. 2), but in at least one subset (discussed in Section 5), endometrial cysts also develop from thin villous folds covered by luminal epithelium. Hyperplastic endometria frequently become inflamed and infected (or vice versa), and the condition may progress to development of pyometra, with possible life-threatening systemic illness.
Other endometrial lesions related to CEH: endometrial polyps
Small aggregates of cystic endometrial glands sometimes stimulate deposition of interstitial fibrous connective tissue that can expand and protrude to form endometrial polyps. Bitches and queens may have only one or several endometrial polyps, which are frequently small and of little consequence (Fig. 7A). Occasionally larger polyps develop that can compromise the uterine lumen (Fig. 7B).
Endometrial hyperplasia resembling maternal placental tissues (pseudo-placentational endometrial hyperplasia; PEH)
A second form of endometrial hyperplasia was initially reported nearly 100 y ago [38], and although it is described in standard textbooks [41], [42], it is not widely recognized by clinicians or diagnostic pathologists. As with CEH, it occurs primarily during the luteal phase of the cycle when the endometrium is highly sensitive, as demonstrated in a series of papers published by Dr. Kochi Nomura and colleagues from the University of Osaka Prefecture [18], [19], [20], [21], [22], [23], [24],
Cysts that arise from uterine tissues other than the endometrium
These cysts can be congenital (i.e., cystic remnants of the male embryonic ductal system) developmental (adenomyosis within the myometrium), or acquired (serosal inclusion cysts that develop from the peritoneum lining the surface of the uterus). An embryonic vesicle could be confused as being a cystic uterine lesion and pregnancy and should always be considered. Most of these lesions can be identified based on location, number and size. There are no data available regarding their relative
Conclusions
Cystic lesions of the canine and feline endometrium are common and can be readily identified based on their location, distribution and morphology, as demonstrated in the subgross photographs presented in this paper.
Proliferative changes involving the endometrium can result in cyst formation. Selecting appropriate descriptive terms to describe these conditions can be difficult, frustrating, and potentially confusing. This is especially true of the endometrium, which changes dramatically during
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