Advances in the ultrasound diagnosis in equine reproductive medicine: New approaches

Abstract

Ultrasound technology has led to new lines of research in equine reproduction, and it has helped to greatly improve clinical diagnosis and reproductive outcomes in equine practice. This review aims to discuss the potential clinical uses and new approaches of ultrasonography in equine reproduction. Doppler modalities are usually used to evaluate the vascularization of the follicles, corpus luteum (CL), and the uterus in the mare for diagnostic purposes. Inclusion of Doppler ultrasound in artificial insemination and embryo transfer programs could improve the reproductive outcome of these techniques. Better selection of recipients based on CL functionality, early pregnancy diagnosis 7-8 days postovulation of the donor before flushing or diagnosis of mares with endometritis with pathological increases of blood flow are examples of clinical applications in the mare. In the stallion, colour Doppler ultrasound has improved the diagnostic potential of B-mode ultrasound, improving the differential diagnosis of pathologies such as testicular torsion (decrease or absence of blood flow in the cord) and orchitis (increased blood flow in the cord). The incorporation of pulsed Doppler ultrasound into the reproductive evaluation of the stallion has enabled early identification of stallions with testicular dysfunction, thus allowing administration of timely treatment and subsequent improvements of the fertility prognosis for these animals. In addition, this technique has been used in the monitoring of patients undergoing medical and surgical treatments, thus verifying their efficacy. Recently, computer-assisted pixel analysis using specific software has been performed in research work in order to semi-quantitatively evaluate the vascularization (colour and power Doppler) and echotexture of different organs. These softwares are now being developed for clinical purposes, as is the case with Ecotext, a computer program developed for the evaluation of testicular echotexture, providing information on testicular functionality.

Keywords: 3D ultrasound; grey scale image; mare; power and colour Doppler; pregnancy diagnosis; pulse Doppler; stallion; subfertility.

FIGURE 1

Summary figure. Advances in ultrasonography increased the clinical applications of this technique in equine reproduction

FIGURE 2

Colour Doppler evaluation of the corpus luteum (CL) in the mare. (a) Colour Doppler ultrasound image of a CL displaying a well‐established homogeneous pattern of vascularization, consistent with an active status of this gland. (b) Colour Doppler ultrasound image of a CL showing an absence of irrigation, indicative of a low functionality

FIGURE 3

(a) Power Doppler ultrasound of a functional CL of 8 days postovulation in a mare. The day 8 postovulation is the day with the highest blood supply to the CL and with the highest production of progesterone. Power Doppler ultrasound is the most sensible technique to assess the vascularization of CL. (b) Endometrial blood flow evaluated with power Doppler ultrasound. Computer‐assisted pixel analysis using Image J software has been performed in research work in order to semi‐quantitatively evaluate the vascularization and echotexture of different organs based on the area and intensity of pixels identified in the image

FIGURE 4

Determination of fetal sex by Doppler ultrasound. Colour Doppler ultrasound image at day 240 of gestation, showing the vascularization pattern characteristic of the male gonad, with the pampiniform plexus and the testicular vein

FIGURE 5

Pathological findings in male reproductive ultrasound. (a) External genitalia from a stallion with heart failure causing ventral oedema. Such tissue swelling could cause problems with the thermoregulation of the testicles as well as mechanical problems when externalizing the penis. (b) B‐mode ultrasound image showing clear anechoic fluid around the testicle, a condition known as hydrocele. (c) B‐mode ultrasound image displaying a cavity with trabeculae between the scrotum and the testicle. This kind image is characteristic of the haematocele. (d) Combination of b‐mode (D1) and colour Doppler ultrasound images of the testicular cord showing a tortuous dilated vein full of fluid (green arrows) but without signs of pulsatility

FIGURE 6

Computer testicular echotexture analysis using Ecotext software in stallions. This software (Ecotext, Humeco, Spain) is a diagnostic method of testicular dysfunction in stallions. According to the manufacturer, Ecotext provides the user with a total of six different parameters: Three parameters at normal resolution: Ecotext 1, Ecotext 2 and Ecotext 3, related to the number of black, white, and grey pixels respectively, and three parameters at high resolution related to hypoechogenic areas: Ecotext tubular density (density of hypoechogenic areas), Ecotext tubular diameter (mean diameter of hypoechogenic areas) and Ecotext tubular area (total percentage of hypoechogenic area)