and caudal to the right.
Figure 10.17 Sagittal view of the ampulla (between small arrows). Note the distended hypoechoic lumen surrounded by gland tissue. Luminal contents may or may not be seen during examination of normal bulls. The lobar tissue above and to the right of the large arrow is an adjacent seminal vesicle. Dorsal is on top, ventral on the bottom, cranial to the left, and caudal to the right.
Figure 10.18 Oblique view of the seminal vesicle (horizontal tissue between arrows). Note the lobar architecture. A short segment of the hypoechoic central duct is seen in the center of the gland between the two arrows.
Pathology of the bulbourethral glands and prostate is uncommon. Aplasia [6] and sperm accumulation [23] have been reported in the ampullae. Inflammation of the vesicular glands is relatively common in bulls and should be suspected whenever an asymmetry in size or echotexture is encountered. Inflamed glands are larger and often have a mixed echogenicity, while abscessed glands show a loss of lobar architecture and often have a globoid area of variable echogenicity [24]. A bacterial infection is most commonly incriminated as the cause of seminal vesiculitis, but sterile inflammation resulting from urine or sperm leaking into the glands is also a potential etiology. Figure 10.19 is an ultrasonogram from a two‐year‐old beef bull with segmental aplasia of the right vesicular gland. Note the cystic dilation of the occluded central duct. The gland was much larger compared with the gland on the left. This bull also had aplasia of the right epididymal tail and a grossly distended hypoechoic right rete testis.
Figure 10.19 Oblique view of the seminal vesicle (above vertical arrows). This bull had a segmental aplasia of the seminal vesicle on this side resulting in the cystic distension of the central duct (horizontal arrow).
Examination of the Penis and Prepuce
Ultrasound can be used to examine the penis, prepuce, and penile urethra. Ultrasonography of the perineal area caudal and dorsal to the scrotum will generally require shaving the hair to obtain good images. The risks associated with ultrasound examination of the penis and prepuce cranial to the scrotum should be balanced with the lower probability of the examination providing valuable diagnostic and prognostic information beyond that obtained by visual inspection and palpation. Direct observation of the penis and prepuce during mating or semen collection is necessary to detect many conditions, such as penile hypoplasia, genital warts, persistent frenulum, hair rings, or balanoposthitis. Ultrasonically relevant lesions affecting the penis and prepuce include trauma, neoplasia, hematoma, abscess, calculi, urethral dilation and rupture, and vascular shunts.
Alternative Ultrasound Modalities
While B‐mode ultrasonography is currently the most commonly employed modality for examination of reproductive tissue, other ultrasound‐based diagnostic methods exist. Color Doppler, contrast‐enhanced ultrasonography and tissue elastography are adjunct imaging modalities used to investigate lesions in human testes [25] as well as other tissues.
The direction, relative velocity, and volume of blood flow in arteries can be assessed by use of Doppler ultrasonography [4]. A color Doppler ultrasonogram of the testicular artery dorsal to the testis within the vascular cone is shown in Figure 10.20. In a recent report using Doppler ultrasound, the resistive index in both the marginal and intratesticular portions (Figure 10.21) of the testicular artery of the bull were correlated with the total sperm in the ejaculate, immature sperm, abnormal sperm, and presence of the Dag defect [26]. Because of the relative ease of marginal testicular artery imaging (located medial to the testis), the authors conclude that this could be an “easy‐to‐perform parameter to evaluate the spermatogenesis quality” in bulls. And while the correlations in this report were significant, there was no evidence that they could be used to establish cut‐off values to distinguish between satisfactory and unsatisfactory breeding bulls.
Figure 10.20 Sagittal view of the vascular cone using color Doppler mode. The direction of blood flow in the supratesticular portion of the testicular artery is indicated by color and the velocity by shade within color.
Figure 10.21 Sagittal color Doppler image of the testis illustrating blood flow (colored areas) in the intratesticular portion of the testicular artery.
Tissue elastography measures the stiffness of tissue in response to an applied force. This force can be applied either mechanically or by the ultrasound waves themselves. A soft consistency of the testis is present in cases of testicular degeneration [27], but manual assessment of testis consistency is limited by both its subjective nature and the presence of intervening scrotal wall with varied skin texture and fat deposits. Mechanical systems that compress the scrotal surface have been proposed [28], but they still have limitations as they must be applied to the scrotal surface and do not directly measure the consistency of the testis. Tissue elastography offers the advantage of both more objective assessment of tissue stiffness and the ability to focus on the tissue of interest within the testis. Most focal lesions of the testes will differ in consistency in comparison to the surrounding normal parenchyma.
It is important to note that most inexpensive portable bovine ultrasound systems lack a color Doppler function and even much more expensive systems do not routinely offer elastography. Given the cost and limited clinical application in bulls, these modalities will be of more interest to researchers than to clinicians for the foreseeable future.
Summary
Diagnostic ultrasound is a safe, non‐invasive method for acquiring additional diagnostic and prognostic information in cases of infertility in the bull. Clinical competence with bull genital ultrasonography can be readily achieved by routinely imaging the genital tract of normal healthy bulls. This will provide the frame of reference necessary to identify and interpret pathologic changes as they are encountered. The common lesions are seldom subtle and are readily detected by systems
