Unilateral Leiomyoma in the Mesosalpinx of a Dog

Introduction

Leiomyomas are reported to be noninvasive, nonmetastatic, and slow-growing structures.¹ They rarely cause clinical signs.¹ In some cases, leiomyomas become extremely enlarged and may exert pressure on the internal organs and cause pain.² Usually they are coincidentally detected during necroscopy or ovariohysterectomy.²

Leiomyomas and leiomyosarcomas of mesenchymal origin may be located within the digestive system, heart, ovaries, uterus, and vulva of dogs and cats.² In one report of canine uterus tumors of mesenchymal origin, leiomyomas accounted for 85% to 90%, and leiomyosarcomas accounted for 10% of the masses.² In a retrospective study involving 49 dogs with ovarian tumors, only one (2.04%) bitch had a leiomyoma of ovarian origin.³

The purpose of the case reported here is to present the ultrasonographic evaluation of a rare case of leiomyoma located at the mesosalpinx of a dog.

Case Report

A 3-year-old, intact, female terrier was presented to the Obstetrics and Gynecology Department of the Veterinary Faculty of Ankara University for routine gynecological examination. On physical examination, there was no vulvar edema or discharge. On vaginoscopy, the cervix was closed, and there was no mucosal folding or edema of the vaginal mucosa. The general condition and appetite of the dog were good.

The uterus and ovaries were ultrasonographically evaluated by the use of a linear array, 8-MHz^a probe. On ultrasonography, the uterus was normal. A mass was visualized ventrocaudal to the left kidney (i.e., at the level of the ventral edge of the kidney), and it had lower echogenicity than that of the renal cortex [Figure 1]. The mass was easily distinguished from the neighboring tissues by its size (1.71 × 1.64 cm), oval shape, and irregular borders on the side nearest the kidney. The mass was not attached to the kidney. The mass contained two oval, cyst-like structures, with anechoic centers that were 0.51 cm and 0.55 cm in size. The mass appeared to mimic an ovary with follicular structures. Acoustic enhancement was noted within the distal part of the mass. Further examination revealed that the mass was just ventral to the left ovary [Figure 1] and was thought to be adherent to the ovary. No stalk was observed between the mass and left ovary. The size of the left ovary was 1.1 × 0.9 cm. The echogenicity of the ovary was significantly higher than that of the mass. No follicular structures were detected on the left ovary.

The right ovary was easily imaged. It was smooth, oval-shaped, located near the caudal pole of the kidney, and had similar echogenicity to the renal cortex. Structures with lower echogenicity than the ovarian parenchyma were detected and were compatible with regressing corpora lutea.

Considering the probability that the mass was a tumor, the rest of the abdomen was thoroughly evaluated. The intestinal loops observed around the structure appeared normal. There was no corrugation of the intestines, and no ascites was observed.⁴ The ipsilateral kidney was normal.

Vaginal samples were stained via the Papanicolaou method, revealing abundant parabasal and small intermediary cells and a few neutrophils. No erythrocytes were detected. A blood sample was submitted for hormonal assays. Serum progesterone and 17 ß estradiol values were determined by radioimmunoassay (RIA)^b and were normal for late diestrus (2.76 ng/mL, reference range 2 to 10 ng/mL; 3 pg/mL, reference range 2 to 7 pg/mL, respectively). Based on vaginoscopic, vaginal cytological, and hormonal test results, the mass was considered to be nonfunctional tumor adherent to the ovary.

Exploratory laparotomy revealed no fluid accumulation in the abdomen. The mass was connected to the ovarian bursa of the left ovary by a thin, small stalk. No adhesions to any other organs or adjacent structures were found, and there were no apparent metastatic lesions on the intestines, kidneys, or surrounding tissues. Both ovaries and the uterus were surgically removed along with the mass.

The mass was fixed in 10% buffered formalin for routine histopathological evaluation by the Department of Pathology, Faculty of Veterinary Medicine, Ankara University. Grossly, the mass was 2.5 × 2 × 1.5 cm in size, with a weight of 5 g [Figures 2A, 2B]. The mass was smooth and well defined. On microscopic examination, the mass was composed of oval or round cells that swirled in various directions [Figure 3A]. Based on the results of Masson’s trichrome staining [Figure 3B], the cells were identified as smooth muscle cells, and the diagnosis was established as leiomyoma.

Discussion

Leiomyomas and leiomyosarcomas of the canine genital system rarely cause clinical signs and are usually detected coincidentally during necroscopy or ovariohysterectomy.⁵ Similarly, the leiomyoma in the case presented here was coincidentally detected during ultrasonography conducted during routine gynecological examination. The dog was clinically asymptomatic, and vaginoscopic, vaginal cytological, and hormonal evaluations indicated no sexual activity.

Leiomyomas in bitches have been reported to produce estrogen and progesterone.¹ The neoplastic transformation of myometrium into a leiomyoma in humans may involve somatic mutation of normal myometrium and complex interactions of local growth factors and ovarian steroids.⁶ The estrogen and progesterone levels in the dog reported here were within reference ranges, which suggested that the mass was not secreting significant levels of estrogen or progesterone. Because the mass was located in the mesosalpinx and had no direct relationship to the ovary, it would likely have been hormonally inactive.

Ultrasonography is a reliable tool for the detection of abdominal masses.^7,8 The ultrasonographic appearance of leiomyomas of the genital organs of dogs has not been previously described. Ovarian and uterine tumors have been reported to be heterogeneous on ultrasonography, regardless of whether they are malignant or benign.^8,9 In the present case, the hypoechoic appearance of the leiomyoma allowed both its definition and detection.

Conclusion

A leiomyoma of the mesosalpinx was detected on abdominal ultrasonography in a 3-year-old, female terrier. The leiomyoma was not associated with the production of steroid hormones or any clinical signs. Definitive diagnosis was achieved by histopathological evaluation, although ultrasonography was a reliable diagnostic tool for identification and localization of the mass.