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Reproductive ultrasonography in males: Normal studies (Proceedings)
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).
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 Male Reproductive Tract: Dog and Tom
The male canine reproductive tract consists of the male genital organs including the scrotum, the two testes (normally located within the scrotum), the epididymides, the deferent ducts (leading from the epididymis to the urethra), the spermatic cords, the prostate, the penis and the urethra. The scrotum is a pouch divided by a thin wall into two cavities, each of which is occupied by a testicle, an epididymis, and the tail end of the spermatic cord. The skin of the scrotum is covered with fine hairs. The dartos of the scrotum is a layer of tissue that lies just under the skin and is made up of muscle and other tissue. Under the dartos is connective tissue lining the scrotum. Each testicle is oval in shape and thicker centrally. The testicles contain seminiferous tubules. The epididymis is comparatively large in the dog and consists of an elongated structure composed of a long convoluted or twisted tube. It begins at the cranial aspect of the testicle and is positioned along the edge. The deferent ducts are thin muscular tubes that are made up of three layers. The prostate gland surrounds the neck of the bladder, as well as the distal ductus deferens. A thin wall divides the gland into two equal-sized smooth, firm lobes. The prostate has multiple openings into the urethra. The penis is a highly vascularized structure. It is composed of several parts, including the root, body and distal portion or glans penis. The root and body are made up of a vascular expansile tissue, the glans, and the os penis. During copulation, the glans penis swells permitting the copulatory lock. The penis also surrounds the termination of the urethra and is important in directing the stream of urine to the outside of the body. The prepuce is the tubular sheet of skin that covers the free part of the non-erect penis.
The reproductive tract of the tom cat consists of the penis, the scrotum, two testicles, the prostate gland, two bulbourethral glands (Cowper's glands), the epididymis, the ductus deferens (also called the vas deferens), the spermatic cords, and the urethra.
The penis is located within the prepuce. When the penis is not erect it is completely enclosed within the prepuce, which is visible on the caudal aspect of the body between the two pelvic limbs. The penis is covered by a protective sheath called the prepuce. The tip of the penis is called the glans, and it is covered with 120 to 150 penile spines that are directed caudally, away from the end of the glans. These penile spines start to appear at about 12 weeks of age and are fully developed at puberty. They are absent in neutered male cats, disappearing by six weeks after castration. The penis is a highly vascularized structure. It surrounds the termination of the urethra and is important in directing the stream of urine to the outside of the body.
The scrotum is located just ventral to the anus and dorsal to the prepuce. It is visible when the tail is lifted upwards. The scrotum is covered with dense hair and is not pendulous. The scrotum is a pouch divided by a thin wall into two cavities, each of which is occupied by a testicle, an epididymis, and the tail end of the spermatic cord. The dartos of the scrotum is a layer of tissue that lies just under the skin and is made up of muscular tissue. Under the dartos is connective tissue that lines the scrotum.
The testes, or testicles, are normally located within the scrotum. Each testicle is round to oval in shape. The testicles contain the seminiferous tubules. The epididymis is an enlarged tube positioned along the edge of the testicle. Its beginning and end (head and tail) are located at the cranial and caudal aspects of the testicle, respectively.
The deferent ducts are thin muscular tubes that are made up of three layers. The ductus deferens or vas deferens begins at the tail of the epididymis and runs along the border of the testicle, and then towards the caudal aspect of the abdomen. It passes through the prostate and empties into the urethra. The two spermatic cords are composed of the ductus deferens, and the vessels and nerves of the testicles. They are covered by a thin membrane. Each cord originates at the tail of the epididymis and extends through the inguinal canal.
The urethra extends from the urinary bladder to the very tip of the penis. The feline penile urethra is very narrow and much shorter than the urethra of the dog. The prostate gland is very small in the cat. It is normally located at the cranial aspect of the rim of the pelvis caudally in the abdominal cavity. The prostate gland surrounds the proximal portion of the urethra and the termination of the ductus deferens. The bulbourethral glands are situated on either side of the urethra. The prostate gland surrounds the proximal urethra, as well as the distal ductus deferens. The prostate has multiple openings into the urethra. It is very small, relatively unimportant organ in the male cat.
The testes are readily located within the scrotum in the normal dog and tom. Imaging each testis can be facilitated by using the opposite as a stand off structure. The normal testis is uniform in texture with echogenicity similar to the spleen. The mediastinum testis is a thin, centrally located, very hyperechoic line.
The epididymis is seen as a hypoechoic teardrop structure adjacent to each testicle (head cranial to the testis, tail caudal); it will appear coarse and more complex than the echogenicity of the testis. The head of the epididymis is isoechoic to the testis, the tail hypoechoic. The normal tail of the epididymis is about one-third the size of the testicle. The ductus deferens is difficult to visualize. The spermatic cord is adjacent to the head of the epididymis and has obvious, tortuous, small diameter veins.
The normal canine prostate gland, located in the pelvic canal, has fairly uniform echogenicity, smooth stippled texture, and echogenicity similar to the spleen. Its shape is bi-lobed in the transverse plane and oval in the longitudinal plane. A hyperechoic "butterfly" pattern may be noted in the transverse image that corresponds to the distribution of ductal tissue, having more echogenic connective tissue than the more hypoechoic glandular tissue. The length and height of the prostate gland ranges from 1.3-3.3 cm in mature, 7-30 kg dogs. The lumen of the prostatic urethra is usually not visualized. The periurethral connective tissue is variably imaged as a bright hilar echo. Caudally, the hilar echo may be surrounded by the hypoechoic urethralis muscle. The normal prostatic capsule can be difficult to detect. In the neutered male the prostate will be quite a bit smaller, in fact, it is usually just a pod, or 'flair' bulging out of the width of the urethra. The neutered male prostatic pod will appear isoechoic with the urethra and be much more hypoechoic than the intact male prostate.
The feline prostate gland surrounds the proximal urethra within the pelvic canal, making visualization difficult. Prostatic disorders are, fortunately, uncommon in the tom.