Making the Most of Reproductive and Urogenital Ultrasound in Mares

Employ nontraditional methods to discover more about pregnancies, pathology, and problematic anatomy, all using a transrectal probe.

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Most equine practitioners are adept at wielding their transrectal ultrasound probe for routine procedures like pregnancy diagnosis. Maria Schnobrich, VMD, Dipl. ACT from Rood & Riddle Equine Hospital in Lexington, Kentucky, however, says veterinarians can do much more in the field with the equipment they already have.

“I encourage you to use ultrasound in nontraditional methods using the same equipment you use for routine transrectal examinations,” said Schnobrich during her presentation at the 2021 American Association of Equine Practitioners (AAEP) Convention, held Dec. 4-8 in Nashville, Tennessee. “A lot of transrectal and transabdominal examinations can be done with a simple linear array probe.”

Here are some of the tricks and tips Schnobrich relayed during her presentation:

1. Patient Preparation

A linear high-frequency transducer paired with alcohol or a water-based lubricant will allow you to see up to 15 centimeters depth, which can show you a lot, she said. Even transabdominally, practitioners can use their transrectal probe after wetting down the hair with isopropyl alcohol, (instead of clipping the coat).

2. Interpreting Images

When trying to identify pathology (disease or damage), consider the ultrasound examination findings together with the clinical signs, she said. In addition, use the mare as her own control.

“If you are concerned about pathology, look on other side (of the body),” she said. “Is what you are looking at normal for this mare? Or, you can even palpate or examine another mare” for comparison?

The Doppler feature on ultrasound serves several purposes in broodmares outside of echocardiograms. It can help veterinarians distinguish between solid masses with blood flow and hematomas, for example. It can also help them detect fetal heart rate and, therefore, the presence of a viable fetus.

3. Rapid Pregnancy Diagnosis

While transrectal palpation is important in reproductive medicine, sometimes clients want to confirm pregnancy even more rapidly. Consider, for example, needing to evaluate 50 mares at once before a sale … or finding a fetus in a field full of pregnant mares and needing to determine which one aborted.

“Scanning the area 5 inches cranial (toward the head) to the udder and along the sides of the udder using a transrectal probe will reveal characteristic signs if a mare is greater than 250 days of gestation,” Schnobrich said. “Pregnant mares normally will have an area where the uterus and placenta lie against the body wall. This appears as an echogenic line of tissue (chorioallantois attached to the uterus) with fluid (allantoic and amniotic) and a fetus deep to this line.”

She added, “If this cannot be imaged, then rectal evaluation needs to be performed to confirm pregnancy.”

Further, using the transrectal probe to get a detailed look at the uterus and chorioallantoic interface through the abdominal wall might help identify separation between the two structures in cases of placentitis (e.g., nocardioform or advanced ascending placentitis—inflammation of the placenta). It often reveals a reasonable amount of the fetus in mid- to late gestation. Veterinarians can use the other curvilinear probe to image deeper structures.

“This evaluation does not allow complete assessment of the placenta and fetus as the pregnancy progresses, but it can give an important window or snapshot that may identify pathology and allow rapid treatment of placentitis or determine fetal viability,” said Schnobrich.

Additionally, veterinarians might use transabdominal ultrasound with a transrectal probe to measure combined thickness of the uterus and placenta (CTUP).

“Be sure, though, to choose a region of the uterine wall that is uniform without folding,” said Schnobrich. “Certain pathologies and even sedation can cause folding of the uterus and its attached chorioallantois and artificially increase the CTUP. This might lead to incorrect determination of placentitis and unnecessary treatment.”

Scanning ventral and lateral to (below and alongside) the udder transabdominally with the linear transrectal probe can also allow veterinarians the opportunity to evaluate the character of the abdominal fluid (hemorrhage, GI rupture, air), the serosal surface of viscera, and the endometrium and chorioallantois. Experienced clinicians can also usually image and evaluate the allantoic fluid, amniotic membrane/fluid, and fetus itself.

4. Evaluating the Urinary Tract

Often, noted Schnobrich, repro vets skip right over urinary tract, potentially missing important pathology such as bladder stones, hematomas, and ureteral (pertaining to the ureters, which transport urine from the kidney to the bladder) abnormalities.

“Evaluation of the urinary tract becomes more routine with practice and provides important landmarks such as the vestibulovaginal fold (where the pelvic urethra opens) that marks the division of the vagina and the vestibule,” she said. “Often, pathology like urine pooling and aspiration of air in the vagina or urinary tract can be identified in those areas.”

Additionally, at the trigone (where the ureters attach to the bladder), veterinarians can visualize the ureteral opening and dispelling urine. They can follow the ureters to the kidney, where the probe allows some degree of assessment of kidneys and ureters for calculi, dilation, hematomas, or neoplasia (tumors).

Take-Home Message

Wrapping up her presentation, Schnobrich relayed two more useful tips:

  1. Perform the examination slowly:“If you move your transducer or probe too fast, you can easily skip over a small 2-millimeter-diameter lesion and you will miss it,” she said. “When you slow down, you really start to see things that often may be a clue to the source of subfertility.”
  2. Use both the longitudinal and transverse planes (turn the probe 90 degrees) to localize the lesion’s exact location and anatomic relationship.“The simple transrectal probe is amazing. The more you use it, the more you’ll see what you can do with it and push the limits of what we do,” concluded Schnobrich.


Written by:

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she’s worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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