Generally, coping with disorders in small animal reproduction, is a rewarding subspecialty in veterinary medicine. Clients
owning pets with urogenital problems are usually very motivated to achieve resolution. Although demanding of the clinician's
time and expertise, the breeder client tends to be very loyal and compliant. A good reproductive practice generates its own
referrals, and usually is quite busy. Obstetrics and pediatrics are undeniably rewarding parts of the specialty for veterinarians
and their staff. Reproductive practice incorporates the interesting fields of physiology, endocrinology, embryology, genetics,
metabolism, nutrition, pediatric and maternal critical care, anesthesia, pharmacology and anatomy. The field is uniquely requires
expertise in medicine, ultrasonography and surgery.
Diagnostic ultrasonography has become an important component of small animal theriogenology since its introduction to practice
in 1978. The use of ultrasound as a tool in canine and feline reproduction has expanded from its initial role in early pregnancy
diagnosis to its current use in the approach to clinical reproduction (obstetrics, infertility, urogenital disorders and pediatrics).
The availability of ultrasonography in veterinary practice increased as reasonably priced, better quality diagnostic ultrasound
equipment became commercially available to veterinarians. Ultrasonography has become a standard of practice in many communities,
with diagnostic ultrasound available at primary private practices, via readily accessible referral centers or from mobile
specialty practices. Veterinary school curricula and continuing education courses now commonly include ultrasonography, providing
students and graduates with the training to perform and interpret diagnostic ultrasound. Recent developments in scanhead technology
have allowed improved visualization of reproductive anatomy.
Normal 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
Serial evaluation of the ovaries (3 times daily!) can be used to detect changes suggesting ovulation has occurred. During
proestrus, multiple anechoic follicular cystic structures can be identified, enlarging with time (up to >1 cm in diameter).
These structures ultimately have distinct walls and anechoic fluid centers with distal enhancement. The surface of the ovary
may become irregular or lumpy. The anechoic fluid filled follicles acutely become hypoechoic to hyperechoic corpora hemorrhagica
(CH) at the time of ovulation, progressing over several days to hypoechoic corpora lutea (CL). The ovarian follicles do not
collapse in the bitch and queen. During diestrus the ovaries may be lobular, the corpora lutea are obvious hypoechoic structures
of variable size. Precise ovulation timing is best accomplished with a combination of techniques: vaginal cytology, serum
progesterone levels, LH assays, vaginoscopy, with ultrasound providing confirmatory information.