Читать книгу Equine Reproductive Procedures - Группа авторов - Страница 19

Оглавление

8 Ultrasound Evaluation

Patrick M. McCue

Equine Reproduction Laboratory Colorado State University, USA

Introduction

Manual palpation should be followed by a systematic ultrasound evaluation of the entire reproductive tract. Ultrasound is used in broodmares to visualize structures in the reproductive tract that cannot be palpated or differentiated on palpation per rectum, such as detection of echogenic follicular fluid, endometrial cysts, and free fluid within the uterine lumen. In addition, ultrasonography is valuable in the early diagnosis of pregnancy, management of twins, and detection of potential ovarian or uterine pathology. Ultrasound also allows for critical evaluation of the events leading to ovulation, such as changes in follicular characteristics and grading of uterine edema.

Equipment and Supplies

Ultrasound machine, obstetrical sleeves (non‐sterile), obstetrical lubricant (e.g. carboxymethylcellulose).

Technique

Ultrasonography should be performed after manual palpation of the reproductive tract (see Chapter 7).

The rectum should be free of fecal material prior to the ultrasound examination.

Obstetrical lubricant is applied to the ultrasound probe and hand, and the probe is introduced into the rectum in the palm of the examiner’s hand.

A systematic examination of the reproductive tract should be performed. The uterus is identified in cross‐section, and the probe is slowly moved from the base of one horn to the tip of that horn while observing the ultrasound image. The probe is often held at a 30–45 degree angle from horizontal so that the cranial tip of the probe is lower than the caudal part of the probe. The uterus is thus held between the probe and the body wall or pelvis for scanning.

The probe is then manipulated to allow for complete visualization of the ovary ipsilateral to the uterine horn just examined.

After the ovarian exam is completed, the ipsilateral horn tip is again identified and the probe is slowly passed distally along the uterine horn to the uterine bifurcation and then proximally up the opposite uterine horn (Figure 8.1).

The position of the probe is again adjusted to evaluate the second ovary before descending back down the adjacent uterine horn.

The final evaluation is of the uterine body, which is usually visualized in a longitudinal plane with a linear transducer.Figure 8.1 Technique for ultrasound examination of the mare reproductive tract. A linear array transducer is shown over the uterine horn. Note that the uterine body has been cut open in this specimen to view the endometrium.Figure 8.2 Ovarian follicles. The larger follicle is developing a thickened echogenic border (arrow).

The entire reproductive tract should be examined in one continuous motion, avoiding disruption in visualization of any part of the tract. Small embryonic vesicles or small areas of pathology may be missed if a continuous scan of the reproductive tract is not performed.

Figure 8.3 Corpus hemorrhagicum (arrow). The interior of the former follicular lumen is filled with echogenic material (i.e., clotted blood).

Figure 8.4 Mature corpus luteum (arrow) consisting of a solid structure of uniform echogenicity.

Figure 8.5 Regressing corpus luteum (arrow).

Interpretation

Ovarian Ultrasound Features

Normal ovarian structures routinely observed with ultrasound are various sizes of ovarian follicles, fresh ovulations, corpora hemorrhagica, corpora lutea, and regressing corpora albicans (Figures ). Ovarian follicles contain clear follicular fluid, which results in a black image on ultrasound. Ovulation is initially detected as the absence of a previously noted large follicle in a mare in estrus. After ovulation, the follicle fills up with blood, forming the corpus hemorrhagicum. This structure is detected as a homogenous, diffusely gray image on ultrasound. The corpus hemorrhagicum matures into the corpus luteum within 2–5 days and takes on a more echogenic (whiter) ultrasonographic appearance.

Figure 8.6 Hemorrhagic anovulatory follicle. The distinguishing feature was swirling, unclotted blood in the former follicular lumen.

Figure 8.7 Echogenic strands within a follicular lumen early in the progression toward a luteinized anovulatory follicle.

Ultrasound can also help differentiate pathologic conditions of the ovary, such as persistent anovulatory follicles, ovarian tumors, and cystic structures (Figures ). Persistent anovulatory follicles are initially recognized by the presence of multiple echogenic particles within the follicular fluid. Anovulatory follicles often subsequently develop numerous echogenic strands throughout the follicular lumen and usually completely fill in with echogenic material.

The most common ovarian tumor is the granulosa cell tumor, which is usually recognized as a large, multicystic structure with a small, inactive ovary present on the contralateral (opposite) side (Figures 8.10 and 8.11).

Uterine Ultrasound Features

Mares in estrus may have an edematous uterus and may have a small amount of free fluid present within the lumen of the uterus. Edema is best recognized on ultrasound of a cross‐section of a uterine horn as a “sand dollar” or “spoke wheel” appearance. Edema indicates that elevated levels of estrogen and low levels of progesterone are present. Estrogen concentrations and degree of edema increase during estrus and peak approximately 1 day prior to ovulation. Consequently, the degree of uterine edema may be used as an indicator of when to breed as well as a prognostic indicator of ovulation (Table 8.1). Uterine inflammation may be suspected if edema appears excessive or persists post‐ovulation.

Figure 8.8 A pair of luteinized anovulatory follicles.

Figure 8.9 Parovarian cyst. The cystic structure (arrow) is adjacent to the ovary.

Figure 8.10 Granulosa cell tumor consisting of multiple cysts within an enlarged ovary.

The uterus in diestrus is affected by elevated levels of progesterone and has a tubular, homogenous appearance without edema or free fluid within the uterine lumen. The presence of free fluid within the uterine lumen during diestrus is suggestive of inflammation and/or infection (Figure 8.12). Tables 8.2 and 8.3 show the classification of uterine fluid volume and its echogenic character.

Figure 8.11 Normal ovary contralateral to the ovary with a granulosa cell tumor. This ovary is small and inactive (note only one small follicle is visible; arrow).

Table 8.1 A scoring system used to evaluate uterine edema in mares.

Edema Score	Edema Amount	Description
0	None	No edema present; individual endometrial folds not discernable homogenous echotexture typical of diestrus or anestrus
1	Slight	Endometrial folds easily observed in a light “spoke wheel” pattern; edema may be more evident in uterine horns than uterine body Typical of early estrus as the dominant follicle is developing or late estrus prior to or at the time of ovulation
2	Moderate	Endometrial folds increased in thickness; edema pattern obvious throughout uterus Typical of mid‐estrus and usually represents the peak estrogen effect noted 1–2 days prior to ovulation
3	Heavy	Large distended endometrial folds; exaggerated degree of edema Not typical of a normal mare in estrus; may be associated with uterine inflammation; sometimes called hyperedema

Figure 8.12 Echogenic fluid within the uterine lumen (arrow).

Table 8.2 Classification of uterine fluid volume.

Classification	Initials	Score
No fluid	0	0
Trace (<1.0 cm depth)	T	1
Small volume (1–2 cm depth)	S	2
Moderate volume (2.1–5 cm depth)	M	3
Large volume (>5.0 cm depth)	L	4

Table 8.3 Classification of the echogenic character of uterine fluid.

Classification	Score
No echogenic particles (i.e., clear)	4
Slightly echogenic (i.e., slightly cloudy)	3
Moderately echogenic	2
Highly echogenic	1