Bilateral Segmental Aplasia with Unilateral Uterine Horn Torsion in a Pomeranian Bitch

Introduction

Segmental aplasia of a uterine horn results from segmental defects in the development of the Müllerian duct system.¹ In this condition, portions of the uterine horns may be absent, resulting in the isolation of cranial segments from the distal segments and the uterine body.² Secretions and sloughed epithelial cells become inspissated and often form soft, tan concretions within the distended isolated lumen of the uterine horn proximal to the area of segmental aplasia.³ Affected bitches are unlikely to have clinical signs unless they develop pyometra.⁴ This report describes unilateral uterine horn torsion secondary to bilateral segmental aplasia of the uterine horn in a Pomeranian bitch, which caused clinical signs necessitating a veterinary consultation and surgery.

Case Report

A 5 yr old female Pomeranian weighing 3.2 kg presented to the referring veterinarian with signs of chronic abdominal distension (lasting several months) and acute lethargy and anorexia (4–5 days). The complete blood count and serum biochemistry panel were reportedly unremarkable. A large soft-tissue mass occupying the ventral abdomen was seen on radiographs, which prompted a tentative diagnosis of bladder atony and bacterial cystitis. The bitch was treated with enrofloxacin (5 mg/kg subcutaneously q 24 h) for 4 days; however, there was no improvement, and the dog was referred.

At the time of referral, physical examination revealed a 5–6 cm wide, firm, irregularly shaped mass palpated just cranial to the urinary bladder. The complete blood count disclosed a mild, normocytic, normochromic anemia (packed cell volume was 34%; reference range, 37–55%) and a mild leukocytosis (18.8 × 10³/mL; reference range, 6.0–17.0 × 10³/mL) characterized by a mature neutrophilia (13.9 × 10³/mL; reference range, 2.8–9.1 × 10³/mL) and monocytosis (1.8 × 10³/mL; reference range, 0.59–0.85 × 10³/mL). Serum biochemistry was unremarkable except for a mild elevation in C-reactive protein (2.9 mg/dL; reference range, 0–1 mg/dL). These findings suggested inflammation. A large, soft-tissue density occupying the ventral abdomen with dorsal displacement of the colon and small bowel were noted on radiographs (Figure 1A). Abdominal ultrasonography revealed that both the right and left uterine horns were markedly enlarged and contained echogenic fluid. In the caudal portion of the left uterine horn, a corkscrew-shaped structure connecting to the dilated uterine horn was identified (Figure 1B). On the basis of the clinical, radiographic, and ultrasonographic findings, a tentative diagnosis of either pyometra or hydrometra with uterine horn torsion was made, and an exploratory laparotomy was performed.

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The bitch was premedicated with butorphanol^a (0.2 mg/kg IV), midazolam^b (0.1 mg/kg IV), and meloxicam^c (0.2 mg/kg IV) and anesthetized with propofol^d (6 mg/kg IV). An endotracheal tube was placed, and anesthesia was maintained with isoflurane^e in oxygen. The abdomen was opened via a ventral midline incision. A small amount of dark, serosanguineous fluid was collected from the abdominal cavity. The fluid was classified as a nonseptic exudate (nucleated cell count was 18,600/μL, protein content was 2.6 g/dL, and specific gravity was 1.024). Surgical exploration of the abdomen confirmed that the left uterine horn was markedly enlarged with a 1,080° clockwise torsion of the caudal portion of the horn (Figure 2A). The surface of the left uterine horn was dark red, and several adhesions with neighboring organs were present (Figure 2A and Figure 2B). The left uterine horn contained a large volume of dark red-brown fluid consisting of neutrophils, macrophages, and erythrocytes. No etiologic agents were observed. The caudal portion of the horn was a cord-like structure connected to the uterine body (Figure 2B). The right uterine horn was also markedly enlarged with fluid; however, the surface was smooth and normal in color (Figure 2C). The fluid in the right uterine horn was light yellow and contained neutrophils, macrophages, and a few erythrocytes. Although there was no torsion of the right uterine horn, its caudal portion was also a cord-like structure connected to the uterine body (Figure 2C). No fluid passed through the cord-like structure despite manual compression. Ovariohysterectomy was performed, and the peritoneal cavity was lavaged with warm, sterile saline. The excised organs were placed in formalin and submitted for histopathology. The bitch recovered well from surgery and was discharged the following day.

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According to the histopathologic analysis, there were hemorrhage, congestion, and edema throughout the wall of the left uterine horn. The endometrium and some parts of the myometrium showed severe necrosis. Eosinophilic fluid and concretions, cell debris, erythrocytes, and fibrins filled the spaces between the smooth muscles. Fibrin thrombi, severe congestion, and dilatation were seen in some blood vessels. The cord-like structure between the left uterine horn and uterine body had no lumen and was composed of connective tissue and blood vessels without endometrium. The left uterine horn was diagnosed as hemorrhagic infarction with torsion and segmental aplasia. In the right uterine horn, the lumen was dilated and some epithelia of the endometrium were either flattened or absent. The end of the dilated part close to the uterine body was a blind tube that did not open into the uterine body. The cord-like structure had no lumen or endometrium, as with the left uterine horn. The right uterine horn was diagnosed with segmental aplasia and hydrometra.

Discussion

Developmental defects of the Müllerian duct system may cause segmental aplasia in various sections of the uterine horn, uterine body, and vagina in bitches.^5–7 In cats, many cases have been documented.^4,8,9 In bitches, only five cases were found in the English language literature.^4,10 Schulman et al. (1997) reported two bitches with segmental aplasia of the uterine horn.¹⁰ McIntyre et al. (2010) found three bitches with segmental aplasia of the uterine horn among 32,660 bitches that underwent ovariohysterectomy.⁴ One of the five bitches had bilateral segmental aplasia of the uterine horn, and four had only unilateral involvement.

Segmental aplasia of the uterine horn causes fluid accumulation and dilation in the affected uterine horn lying cranial to the occlusion.¹ The affected bitch is unlikely to have any clinical signs, except for abdominal distension, unless complications develop. Most cases of segmental aplasia are found incidentally during ovaryohysterectomy.^4,10 In one bitch, however, the uterine horn developed cystic endometrial hyperplasia, endometritis, mucometra, pyometra and rupture of the uterine horn, leading to severe clinical signs.¹⁰ The bitch in the present report had chronic abdominal distension for several months with an acute onset of anorexia and lethargy, which presumably reflected the occurrence of the torsion.

In bitches, the diagnosis of uterine horn torsion is usually confirmed by exploratory laparotomy. No specific ultrasonographic findings appear to have previously been reported. In the present case, a corkscrew-shaped structure connecting to the dilated uterine horn was found ultrasonographically. Finding this unique structure might lead to a preoperative diagnosis of uterine horn torsion. Although color flow Doppler imaging was not performed in the present case, it has been used for diagnosing canine testicular and splenic torsions.^11,12 The occurrence of uterine horn torsion is higher in the gravid than nongravid uterus. Torsion of the nongravid uterus has been reported in conjunction with other uterine pathologic findings, such as hematometra, pyometra, and cystic endometrial hyperplasia.^13–15

Conclusion

This report describes a case of bilateral segmental aplasia of uterine horns with unilateral torsion and pyometra.

To the best of the authors’ knowledge, this is the first report of uterine horn torsion secondary to segmental aplasia of the uterine horn in the bitch.