**4. Gross morphology**

The gross morphological signs vary according to the defect and also the co-existence of secondary diseases or other concomitant uterine or vaginal disease.

### **4.1 Unilateral uterine aplasia (Unicornuate uterus)**

In unicornuate uterus situations, aplasia of one uterine horn is the major finding, as it is reduced to a fibrous threadlike structure (Figure 1A and 1B), composed of fibrous tissue

originate from the vaginal plate. Degeneration of the center of the vaginal plate creates the vaginal lumen. A hymen may persist where the vagina joins urogenital sinus although in most domestic species it tend to disappear before puberty. The urogenital sinus forms the

Apart from some remnants of the excretory tubes and a small portion of the mesonephric duct, with varying importance according to the species, all the female mesonephric

The cause and heritability of congenital abnormalities in dogs remain undetermined (McIntyre et al., 2010). With exception for the situations accompanying intersex conditions, the karyotype is normal. We are unaware if the condition develops in consequence of genetic, endocrine, or environmental influences. Neither it is known if it might be associated to failure of the gonad or the mesonephros development (which absence may co-exist with the *uterus unicornis*), to failure in local gene expression or, in the case of a segmental aplasia, if it might be determined by disruption of the blood supply to the affected segment (Ribeiro

A *unilateral uterine aplasia* (also termed unicornuate uterus) develops when one paramesonephric duct fails to develop; this results in a uterus with one uterine horn (Moore & Persaud, 2008). The kidney and the paramesonephric ducts have the same embryologic origin therefore this anomaly is usually associated with ipsilateral kidney absence (Chang et al., 2008). Unilateral uterine aplasia has been reported in dogs and cats (Schulman & Bolton, 1997; Pinto Filho et al., 2001; Güvenç et al., 2006). However, the ovary is of a separate embryological origin and is usually present (Moore & Persaud,

Development defects of the Müllerian duct system may cause *segmental aplasia* in several portions of the Müllerian duct system. Partial or complete fusion or occlusion of one uterine horn, of the body of the uterus, or of the most caudal segments, such as the cervix and cranial vagina, may cause fluid accumulation cranially to the occlusion (McEntee, 1990; Oh et al., 2005; Romagnoli & Schlafer, 2006; Almeida et al., 2010; McIntyre et al., 2010). Failure of canalization of the vaginal plate results in atresia (blockage) of the vagina, originating a *transverse vaginal stenosis* or a segmental aplasia, which is found between the middle and the caudal third of the vagina (Schlafer & Miller, 2007). Isolated vaginal atresia is an extremely

Given the many variables that are involved in the female genital tract differentiation and growth, the pathogenesis for each anomaly may be multifactorial and hence of difficult

The gross morphological signs vary according to the defect and also the co-existence of

In unicornuate uterus situations, aplasia of one uterine horn is the major finding, as it is reduced to a fibrous threadlike structure (Figure 1A and 1B), composed of fibrous tissue

secondary diseases or other concomitant uterine or vaginal disease.

**4.1 Unilateral uterine aplasia (Unicornuate uterus)** 

vestibule (Noden & de Lahunta, 1985; Moore & Persaud, 2008).

derivates atrophies (Moore & Persaud, 2008).

et al., 2009; McIntyre et al., 2010).

2008; Thode & Johnston, 2009).

identification (McIntyre et al., 2010).

**4. Gross morphology** 

rare finding.

with some muscle strands (McIntyre et al., 2010) that frequently fail to present a lumen. As the contralateral uterine horn and the other genital segments retain patency, fluid accumulation does not occur unless the female develop cystic endometrial hyperplasia (CEH)/pyometra or other situations of segmental aplasia in the contralateral uterine horn are present (Figure 1A). The non-patent uterine horn may induce fluid accumulation in the oviducts that distend (Figure 1C).

Due to a common embryologic origin, this malformation might co-exist with ipsilateral tubal and renal agenesis (Chang et al., 2008). Although this situation is described with more frequency in cats than in dogs, on its survey McIntyre et al. (2010) found a relative lower frequency of 28% in cats than 45.5% in dogs. Co-existence of renal agenesis appears also on older reports on *uterus unicornis* in female beagles in research colonies (Höfliger, 1971, cited by McEntee, 1990). As those animals were euthanized after the end of the experiments (they integrated the control groups), at young ages, clinical signs were absent. Often the abnormality is detected only at necropsy or surprises the surgeon during the surgery. In contrast, due to a different embryologic origin, most frequently both ovaries are found (Romagnoli & Schlafer, 2006; McIntyre et al., 2010). Other congenital defects besides kidney agenesis were found in animals bearing unicornuate uterus: ectopic contralateral ureter, absent ipsilateral suspensory ligament and umbilical hernia (McIntyre et al., 2010).

Acquired diseases found in described conditions of unicornuate uterus include CEH of the contralateral uterine horn and polycystic ovaries. According to the descriptions, the later could correspond to cystic proliferation of the rete or the cranial uterine tube (Güvenc et al., 2006).

#### **4.2 Segmental aplasia of the uterus**

In cases of segmental aplasia, whether its location may be at the uterine horns, body or cervix, frequently the anomalies are grossly visible as missing segments or strictures that interrupt the normal anatomy of the uterine-vaginal segment, and that correspond to failure of the development of all the layers of that segment, which are often reduced to a streak cord-like rudiment. However, in few situations the external layers of the Müllerian duct derivates (serosal and muscle layers) are properly differentiated, but the inner layers (mucosal and sub-mucosal layers) do not differentiate (Moore & Persaud, 2008). This is more often found in the vagina than the uterus. In practical terms, the potential deleterious effects over the reproductive potential and the occurrence of secondary diseases are similar in the two situations.

As the situation usually remains undiagnosed in young animals that maintain regular reproductive activity, the normally developed portion cranial to the atresia is distended due to fluid accumulation (Figure 1D to 1H). Distension of the uterine tube (Figure 1F) is possible (McIntyre et al., 2010). Primary lesions at the endometrium are rarely reported, but CEH may develop in older animals. However, due to excessive mucous fluid pressure of the ongoing mucometra, with time reduction in the thickness of the uterine walls and compression and attenuation of the endometrial glands is commonly found (McIntyre et al., 2010).

Segmental aplasia of the uterine horns may develop at any point of the structure (Figure 1A, 1C and 1G) (Schlafer & Miller, 2007; McIntyre et al., 2010), with segmental agenesis being irregularly distributed for different segments of the uterine horns.

Congenital Aplasia of the Uterine-Vaginal Segment in Dogs 171

Vaginal stenosis has been described as occurring as a complete misdevelopment of all the layers of the vagina, which may be reduced to an atretic segment with variable importance (Figure 1I) (Gee et al., 1977; Viehoff & Sjollema, 2003; Romagnoli & Schlafer, 2006) or as originating from the absence of internal canalization with normal developmental of the external layers (Wadsword et al., 1978). The existence of a vaginal cyst cranial to the occlusion has been referred, which has been attributed to incomplete canalization of the embryonic derivate, hence allowing the development of intermediary segments between missing portions (Gee et al., 1977; McEntee, 1990). The undeveloped segment is usually located near the vestibulo-vaginal junction (Gee et al., 1977; Kyles et al., 1996; Viehoff & Sjollema, 2003) and on gross evaluation morphology of the anatomical region may share some resemblances with imperforate hymen. The missing segment may present variable

Similarly to the findings for segmental aplasia of the uterine body or cervix, fluid accumulation above the agenesis induces uterine dilatation, but contrasting to those malformations, fluid accumulation also occurs on the remainder cranial segment of the

Vaginal cysts near the point of stenosis have been described (Gee et al., 1977). It has been proposed to correspond to incomplete canalization of atrectic segments (Gee et al., 1977; McIntyre et al., 2010). Impairment of fluid drainage induces fluid accumulation above the obstruction and consequently distension of cranial reproductive tract (Gee et al., 1977; Viehoff & Sjollema, 2003; McIntyre et al., 2010). In contrast to the observed in the previously described situations, fluid accumulates within the uterus (mucometra) and the vagina (hydrocolpos). As vaginal walls are thinner than those of the uterus they distend more easily, thus reaching higher increases in size comparatively to the uterine distension. These morphological features are not exclusive for the segmental stenosis of the vagina. Imperforate hymen shares similar gross appearance (Tsumagari et al., 2001; Schlafer & Miller, 2007), except that the transverse partition is thinner in the later than in the segmental

Congenital abnormalities of the uterine-vaginal segment in dogs are seldom detected before puberty. Furthermore, in a large number of cases remains unnoticed until secondary diseases develop or until unsuccessful attempts for breeding the female alert the owner to the need for a detailed reproductive examination of the infertile animal. Early diagnosis of those conditions would avoid owners to maintain a bitch with severe congenital diseases in the reproductive stock. Also, the correct identification of the disease and evaluation of the importance of the defect would allow proper counselling on the therapeutic approach and establish a prognosis for a specific condition. Further, it will permit to anticipate the occurrence of secondary, associated diseases that can develop if the primary condition is not

The occurrence of unicornuate uterus is rare, but results from different surveys report different relative frequencies. Ortega and Pacheco (2007) in tropical regions reported a

**4.3 Segmental stenosis of the vagina** 

extension.

vagina.

stenosis.

**5. Clinical signs** 

treated and that may threaten the health of the female.

**5.1 Unilateral uterine aplasia (Unicornuate uterus)** 

Fig. 1. Canine congenital aplasia of the uterine-vaginal segment: **A**: The external morphological evaluation showed the complete agenesis of the right uterine horn (unicornuate uterus) co-existing with segmental aplasia of the contralateral uterine horn. Both ovaries (Ov) were present. Arrows indicate areas of agenesis. **B**: Closer inspection showed that the caudal segment of the left uterine horn is patent, while the right uterine horn is reduced to a threadlike structure parallel to the uterine vessels. The ipsilateral ovary (Ov) was present, within the ovarian bursa. Arrows indicate areas of agenesis. **C**: Dilatation of the uterine tube (cyan arrow) ipsilateral to the non-developed uterine horn. **D**: Externally, segmental aplasia of the uterine horn may appear as a marked constriction of the organ. **E**: When opened, those areas showed the absence of fusion between adjacent segments, which fail to communicate. Outside undeveloped areas the uterus maintain its normal morphology. **F**: The ipsilateral uterine tube is distended (arrow), due to fluid pressure. **G**: Segmental aplasia at the basis of the right uterine horn in a 15 years-old bitch (distension of the vagina was due to a fibroma). **H**: The arrow points to the area of aplasia. Long-term effects of the secondary fluid accumulation induced a reduction in the thickness of the walls. **I**: Segmental stenosis of the vagina: the arrow points to the obstruction.

In animals with segmental aplasia of the uterine body or cervix, as communication between the two uterine horns is possible, equivalent and bilateral uterine horn distension is found (McEntee, 1990; McIntyre et al., 2010). Undeveloped segments are usually reduced to cordlike remnants. In cases of cervical aplasia, the uterine body ends blindly in a pouch, a membranous tissue separating the uterus from the vagina (McEntee, 1990).

#### **4.3 Segmental stenosis of the vagina**

170 A Bird's-Eye View of Veterinary Medicine

Fig. 1. Canine congenital aplasia of the uterine-vaginal segment: **A**: The external morphological evaluation showed the complete agenesis of the right uterine horn (unicornuate uterus) co-existing with segmental aplasia of the contralateral uterine horn. Both ovaries (Ov) were present. Arrows indicate areas of agenesis. **B**: Closer inspection showed that the caudal segment of the left uterine horn is patent, while the right uterine horn is reduced to a threadlike structure parallel to the uterine vessels. The ipsilateral ovary (Ov) was present, within the ovarian bursa. Arrows indicate areas of agenesis. **C**: Dilatation of the uterine tube (cyan arrow) ipsilateral to the non-developed uterine horn. **D**: Externally, segmental aplasia of the uterine horn may appear as a marked constriction of the organ. **E**: When opened, those areas showed the absence of fusion between adjacent segments, which

fail to communicate. Outside undeveloped areas the uterus maintain its normal

**I**: Segmental stenosis of the vagina: the arrow points to the obstruction.

membranous tissue separating the uterus from the vagina (McEntee, 1990).

morphology. **F**: The ipsilateral uterine tube is distended (arrow), due to fluid pressure. **G**: Segmental aplasia at the basis of the right uterine horn in a 15 years-old bitch (distension of the vagina was due to a fibroma). **H**: The arrow points to the area of aplasia. Long-term effects of the secondary fluid accumulation induced a reduction in the thickness of the walls.

In animals with segmental aplasia of the uterine body or cervix, as communication between the two uterine horns is possible, equivalent and bilateral uterine horn distension is found (McEntee, 1990; McIntyre et al., 2010). Undeveloped segments are usually reduced to cordlike remnants. In cases of cervical aplasia, the uterine body ends blindly in a pouch, a Vaginal stenosis has been described as occurring as a complete misdevelopment of all the layers of the vagina, which may be reduced to an atretic segment with variable importance (Figure 1I) (Gee et al., 1977; Viehoff & Sjollema, 2003; Romagnoli & Schlafer, 2006) or as originating from the absence of internal canalization with normal developmental of the external layers (Wadsword et al., 1978). The existence of a vaginal cyst cranial to the occlusion has been referred, which has been attributed to incomplete canalization of the embryonic derivate, hence allowing the development of intermediary segments between missing portions (Gee et al., 1977; McEntee, 1990). The undeveloped segment is usually located near the vestibulo-vaginal junction (Gee et al., 1977; Kyles et al., 1996; Viehoff & Sjollema, 2003) and on gross evaluation morphology of the anatomical region may share some resemblances with imperforate hymen. The missing segment may present variable extension.

Similarly to the findings for segmental aplasia of the uterine body or cervix, fluid accumulation above the agenesis induces uterine dilatation, but contrasting to those malformations, fluid accumulation also occurs on the remainder cranial segment of the vagina.

Vaginal cysts near the point of stenosis have been described (Gee et al., 1977). It has been proposed to correspond to incomplete canalization of atrectic segments (Gee et al., 1977; McIntyre et al., 2010). Impairment of fluid drainage induces fluid accumulation above the obstruction and consequently distension of cranial reproductive tract (Gee et al., 1977; Viehoff & Sjollema, 2003; McIntyre et al., 2010). In contrast to the observed in the previously described situations, fluid accumulates within the uterus (mucometra) and the vagina (hydrocolpos). As vaginal walls are thinner than those of the uterus they distend more easily, thus reaching higher increases in size comparatively to the uterine distension. These morphological features are not exclusive for the segmental stenosis of the vagina. Imperforate hymen shares similar gross appearance (Tsumagari et al., 2001; Schlafer & Miller, 2007), except that the transverse partition is thinner in the later than in the segmental stenosis.
