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Performing ultrasound to evaluate pregnancy (Proceedings)

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Apr 01, 2009

Normal (Nongravid) Female Reproductive Tract: Bitch and Queen

The normal uterus is best located by scanning transversely between the urinary bladder and the colon. The cervix and uterine body are seen as a continuous hypoechoic round structure dorsal to the anechoic urinary bladder and ventral to the hyperechoic, crescent shaped colon. Thinking of the urinary bladder as a clock face, the uterine body will be located at 5 o'clock or 7 o'clock. The full urinary bladder acts as an acoustic window to improve imaging the uterus. The cervix is located slightly cranial to the bladder trigone and is best seen when under hormonal influence rather than during anestrus. The cervix is an oblique hyperechoic linear structure in the sagittal view. The uterine body is smaller in diameter than the cervix and usually extends to the cranial one third of the bladder. The bifurcation of the uterus into the uterine horns can sometimes be imaged; the horns are typically difficult to image unless enlarged due to hormonal influence during the estrous cycle, pregnancy, or from pathology. The uterus is composed of three layers: the mucosa, the muscularis and the serosa. The endometrium and myometrium cannot usually be differentiated in the normal state. The uterine lumen is generally not seen, although it may be visible as a bright echogenic central area, representing a small amount of intraluminal mucus, or as a hypoechoic to anechoic region if fluid is present.

The normal ovaries are located caudal and slightly lateral to the caudal poles of the ipsilateral kidneys. Their location can be facilitated by the appearance of the artifactual distal enhancement dorsal to each ovary. The appearance of the ovaries varies with stages of the estrous cycle. Normal ovarian dimensions have been established for average sized dogs. During anestrus, the ovaries appear as small oval to bean shaped structures with a homogenous echogenicity similar to the renal cortex. The cortex and medulla are not usually differentiated in the bitch and queen. Multiple anechoic or hypoechoic cyst like structures can be visualized in the ovarian parenchyma during folliculogenesis, larger cystic structures are present during the luteal phase.

Pregnancy Diagnosis

Pregnancy detection by abdominal palpation (at approximately 30 gestational days) or radiography (43-46+ days post LH peak, the later the better) can confirm the presence of fetuses at these points in time. Prior to fetal skeletal mineralization, other causes for uterine enlargement (hydrometra, pyometra) cannot be ruled out radiographically. Radiography cannot be used to assess fetal viability in a timely fashion. Once profound post mortem changes have occurred, radiography can detect intra-fetal gas accumulation or abnormal skeletal arrangement suggesting fetal death. Early fetal resorption cannot be detected radiographically, only by ultrasound. Ultrasound is the best method to evaluate early in gestation for pregnancy ("yes or no", fetal viability, litter size, and gestational age).

The normal uterus is best located by scanning transversely between the urinary bladder and the colon. The cervix and uterine body are seen as a continuous hypoechoic round structure dorsal to the anechoic urinary bladder and ventral to the hyperechoic, crescent shaped colon. Thinking of the urinary bladder as a clock face, the uterine body will be located at 5 o'clock or 7 o'clock. The full urinary bladder acts as an acoustic window to improve imaging the uterus. The cervix is located slightly cranial to the bladder trigone and is best seen when under hormonal influence rather than during anestrus. The cervix is an oblique hyperechoic linear structure in the sagittal view. The uterine body is smaller in diameter than the cervix and usually extends to the cranial one third of the bladder. The bifurcation of the uterus into the uterine horns can sometimes be imaged; the horns are typically difficult to image unless enlarged due to hormonal influence during the estrous cycle, pregnancy, or from pathology. The uterus is composed of three layers: the mucosa, the muscularis and the serosa. The endometrium and myometrium cannot usually be differentiated in the normal state. The uterine lumen is generally not seen in the non pregnant state, although it may be visible as a bright echogenic central area, representing a small amount of intraluminal mucus, or as a hypoechoic to anechoic region if fluid is present.