Ultrasonography of the normal reproductive tract of the female domestic cat

The objective of this study was (1) to describe the US appearance and obtain reference values for the uterus and ovaries in nongravid and gravid queens with histologically confirmed reproductive tracts without disorders, (2) to provide US measurements of the reproductive tract compared to gross macroscopic and water-bath post-OVH US measurements in nongravid queens, and (3) to describe the sonographic appearance of the female reproductive tract during the different histopathologic phases of the reproductive cycle in nongravid and gravid queens. Ninety-three queens from a “trap, neuter, return” program were included in this study. Sonographic evaluation of the reproductive tract was performed in all queens, and measurements of the corpus uteri, uterine horns, and ovaries were recorded. Following OVH, macroscopic measurements were obtained, and a water-bath US evaluation of these tissues and measurements was recorded. Samples from the corpus uteri and both the uterine horns and ovaries were collected for histopathologic examination after all measurements had been recorded. Seventy-two reproductive tracts met the inclusion criteria by having a histopathologically confirmed normal reproductive tract. Sixty-three queens were nonpregnant and 9 were pregnant. The ovaries and uterus were sonographically visible in all queens regardless of reproductive status. The ovaries were ovoid in shape, and the uterus appeared as a tubular structure with distinct wall layers (serosa and indistinct myometrium and myometrium, or serosa, myometrium, and endometrium), with variable echogenicity of the inner layers. The layering of the uterine wall, observed during the second half of pregnancy, was described. Ovarian follicles were visible in 66/72 (92%) cats. However, the CL was only visible in 40/72 (55%) cats. The reference values of the left ovarian length, right ovarian length, uterine horn diameter, and uterine body are 7.1–13.9, 7.3–13.6, 1–5.8, and 1.5–5.3 mm, respectively, in a nongravid uterus. The uterine wall thickness during pregnancy varied from 2.4 to 6.8 mm. There was a significant positive correlation between US measurements obtained in vivo and those obtained macroscopically and in a water bath post-OVH. The body weight, follicular size, sonographic visibility of the uterine wall layering, the histopathologic luteal phase, and the active/inactive status on histopathology had a significant effect on the uterine measurements (p < 0.05). It was not possible to describe the exact US features of the reproductive tract during the different histopathologic phases.In conclusion, ultrasonographic reference values for the normal female reproductive tract in cats were determined. The results of this study indicated that the ovaries and uterus were visible in cats regardless of reproductive status.