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The application of ultrasound during reproductive and obstetric examinations is enjoying increasing popularity in small animal practice. Ultrasound makes early pregnancy diagnosis possible and usually permits an assessment of the viability of conceptus. Also in its applications to diagnose other pathological conditions of genital tract ultrasound can be considered equally, or even more effective than other diagnostic techniques.
For reproductive and obstetric examinations in dogs and cats transcutaneous sonography is used. The ultrasound probe is positioned externally against the abdominal wall. A trans-rectal approach, using small rectal probes adapted from human medicine, appears feasible in larger bitches. The use of 5 MHz scanners in small animals presents a useful compromise between image quality and scanning depth.
In order to produce an image of the uterus the probe is positioned between the two rows of mammary glands. Its beam is directed ventro-dorsally and it is placed directly in front of the pubic bone. Following this technique it must be remembered that the image closest to the probe originate from the ventral part of the abdomen, while the portion of the image furthest removed from the probe corresponds to the tissues in the dorsal abdomen. In contrast to the situation as it is seen during the trans-rectal scanning of cows and mares the images seen in the trans-cutaneous examination appear upside down. During the trans-rectal examination the uterus lies close to the probe and the urinary bladder somewhat deeper. In contrast, during the trans-cutaneous examination of dogs and cats the urinary bladder will be closest to the transducer with the uterus in the depth of the image. A systematic approach is required is essential if a through examination is to be obtained. The ultrasound examination of internal genital tract should proceed from caudal to cranial. First, the urinary bladder is recognised inside the pelvis. It produces the typical image of hollow, hypoechoic organ and serves as the reference point for the examination. A full bladder is preferred for ultrasound examination. The bladder is easier to find when it is full and acts as an acoustic window, because its fluid contents will cause the relative amplification of the ultrasound passing through it and this facilitates the imaging of structures behind it. Dorsal to the urinary bladder lies the rectum. In transverse section it produces a round cross-section with the surface closest to the transducer producing a bright and convex image. One should attempt to find the pregnant or pathological uterus in the area of fundus of the bladder. Using the bladder as reference point this is possible by moving the scanning plane from side to side. In cats, and occasionally in dogs, in dorsal recumbency the uterine horns can lie far laterally. They can be moved into the image by moderate finger pressure onto the abdominal wall.
The ovarian structures: With currently available ultrasound equipment, diagnostic ultrasonography of canine and feline is restricted to the detection of pathological conditions. Follicles and corpora lutea, which are normally only few millimeters in diameter, are too small to be detected reliably.
Ovarian tumors and cysts: Some pathological changes on the ovaries of dogs and cats are sonographically recognizable. Suitable indications for the use of ultrasound include ovarian tumors and cysts. Cystic ovaries in the bitch can produce ultrasonograms, which appear honeycombed in structures and contain numerous anechoic cavities. The cysts vary in size, are fluid filled and separated from one another by thin, echoic walls. Large parts of ovarian tumors are made up of hypoechoic, solid tissues. In places anechoic, fluid filled structures are placed in the tumor.
Uterus: important indications for the sonographic examinations of dogs and cats include pregnancy diagnosis and the recognition of pathological changes in the uterus.
Pregnant uterus:
Before Day 20 of pregnancy: If high-resolution ultrasound is used it may occasionally be possible to detect signs of pregnancy on ultrasound before day 20 of pregnancy. It has been reported that hypoechoic areas of few millimeters in diameter could be found in the regions of the developing conceptus as early as the second week of pregnancy.
Day 20 to 30 of pregnancy: From day 20 of pregnancy, it becomes possible, under practical conditions, to diagnose a pregnancy in a bitch or queen. The conceptus which are filled with hypoechoic embryonic fluid can be seen on the ultrasound monitor. They are surrounded by echoic uterine wall. On day 20 the conceptus have an inner diameter of 10 to 20 mm. Under practice conditions a reliable pregnancy diagnosis using 5 MHz transducer is possible in most of the cases from day 25 or gestation. In order to avoid misdiagnosis, other fluid filled bodies must be differentiated from the conceptus. In particular, blood vessels and loops of intestines that run in the vicinity of the urinary bladder must be considered. The cross-sections through larger blood vessels adjacent to the uterus can appear very similar to the conceptus. Rotation of the transducer will reveal the longitudinal shape of the blood vessel and the spherical shape of the conceptus.
Inside the embryonic echoes, a heartbeat will become detectable between day 28 to 30.
In dogs it is possible to assess the development of the conceptus and the gestational age by fetometry. Thus far data have been collected for the following parameters: Crown-rump-length and biparietal, abdominal and cardiac diameters, as well as the size of one rib cross-section with one inter-costal space. The ultrasonographically measured crown-rump-lengths largely correspond to those obtained after removal of fetus from the uterus.
Long axis ultrasound image of post-partum uterus was tubular in shape. The short axis shape of the uterus was initially often flaccid appearing. It varied from circular to crescent shaped to polygon. This lasted until 2-4 week post-partum, during which time the short axis uterine shape gradually changed to circular.
Uterine pathology:
The use of ultrasound for post partum or post oestral checks will allow early detection of potential uterine pathology. Ultrasound will allow differentiation of 1) uterine cysts (focal fluid filled areas), 2) pyometra (fluid with increased echogenicity), 3) dead foeti (no heart beat), 4) resorbing foeti (poorly delineated gestational sacs with or without fetal remains), 5) premature placental separation (fluid between uterine wall and placental tissue).
The recognition of markedly fluid filled pyometra s in bitches is easy. In well-developed pyometra s, the accumulated fluid leads to severe distention of the uterus. Frequently, the uterus does not produce an image of a long, fluid filled tube, but rather shows thin sections of uterine wall appearing inside the fluid at irregular intervals and creating a compartmentalized image of the uterus. This image originates from the severe twisting of the uterine horns, sections of which, sometimes completely kinked, come to lie close together. The echogenicity of pyometra exudate varies between almost anechoic and moderately echoic. It primarily depends on the degree of cellularity or the exudate.
PHYSICS OF ULTRASOUND| MERITS| LIMITATIONS| EYE| HEART| LIVER| SPLEEN| KIDNEY| BLADDER AND PROSTRATE| PANCREAS| GI TRACT| TESTIS| REPRODUCTION AND OBSTETRICS