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 | Ultrasonographic Image |
|---|---|---|---|
| 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 |
