18.1). The mediastinum testis is a readily identifiable hyperechoic area in the center of the testicle when viewed in the transverse plane or a hyperechoic line when viewed in the sagittal plane (Figure 18.2). The head, body, and tail of the epididymis are less echogenic than the testicle and are readily identified as they course along the testicle. Thickness of the scrotal skin and vaginal tunics and the presence of fluid within the vaginal cavity are readily determined.
Figure 18.1 Ultrasound of normal testis in transverse plane. Mediastinum testis is hyperechoic area in center of testis.
Figure 18.2 Sagittal ultrasound of normal bovine testicle. Mediastinum testis is hyperechoic line in center of testis.
Thermography of the Scrotum
Testicular temperature must be below body temperature for normal spermatogenesis in bulls. Infrared thermography provides a non‐invasive, non‐contact imaging technique to determine normal and abnormal thermal patterns in bulls and other animals [5]. Thermography utilizes sensitive infrared imaging to produce a color photograph that portrays variations in surface temperature that reflect the temperature of tissues immediately beneath the skin. The normal thermogram of the scrotum in all species is a left and right symmetric pattern with a constant decrease in temperature gradient from the base to the apex (Figure 18.3). In bulls a temperature gradient of 4–6 °C from base to apex is considered normal. A gradual decrease from base to apex with concentric color bands is consistent with normal function of the vascular counter‐current heat‐exchange mechanism of the testes. An excessively cool or excessively warm area as evidenced by thermographic color is consistent with testicular disease or injury [6, 7] (Figure 18.4).
Figure 18.3 Normal thermographic pattern of bull scrotum.
Figure 18.4 Thermograph of scrotum of bull with unilateral pathology. Note decreased temperature on left side of scrotum.
Semen Evaluation
Semen from bulls with significant scrotal or testicular pathology generally does not meet the minimum 70% morphologically normal sperm of which more than 30% are progressively motile, and these bulls are thus considered subfertile. The temporal appearance of sperm abnormalities following scrotal insulation has been established in bulls and may be useful in determining the chronicity of an insult [2, 8, 9]. Semen evaluation may also be used to determine when surgical intervention should be pursued in bulls with unilateral testicular disease.
Scrotal and Testicular Disease and Injury
Fluid Accumulation in the Vaginal Cavity
Fluid accumulation in the vaginal cavity is a common cause of scrotal enlargement in bulls. This accumulation can occur bilaterally, but unilateral enlargement is more common. The condition can be further defined by the type of fluid present. Hemorrhage in the vaginal cavity commonly results from trauma and is known as a hematocele. Injury or periochitis can cause the accumulation of an inflammatory exudate or transudate in the vaginal cavity which is referred to as a hydrocele [10]. Bilateral scrotal hydroceles have been reported in bulls secondary to ascites caused by gastrointestinal parasitism [11]. Fluid accumulation in the vaginal cavity causes distention of the parietal vaginal tunic, creating the appearance of testicular swelling. Depending on the nature of the fluid present and the degree of distension of the parietal vaginal tunic, the affected side may palpate firm and the testicle itself may be hard to identify. The presence of fluid in the vaginal cavity can easily be confirmed with ultrasound (Figure 18.5). Fibrinous and fibrous adhesions between the testicle and the parietal tunic may also be visible on ultrasound.
Figure 18.5 Ultrasound of scrotum of a bull with a hydrocele. Note anechoic fluid distention of vaginal cavity.
Source: Image courtesy of Darcie Sidelinger and Heath King.
Orchitis, Periorchitis, and Epididymitis
Orchitis is uncommon in bulls and usually unilateral. Infection is often subclinical but rarely may range to severe and perhaps suppurative [12, 13]. The route of infection is primarily hematogenous but penetrating wounds of the scrotum are also possible. The dense fibrous tunica albuginea surrounding the testicle limits this organ's potential for enlargement and therefore there is usually not significant testicular swelling. However, when infection involves the surrounding tunica vaginalis (periorhitis), significant scrotal enlargement can occur. The affected side may also be warm and painful to the touch, with pain significant enough to alter the gate of the bull [12].
Epididymitis occurs more commonly than orchitis in bulls and may be diagnosed by thorough examination of the testes and scrotal contents [14–16]. The condition is often unilateral in the bull and may present as a swollen painful epididymal tail in the acute phase of the disease. Chronic epididymitis usually results in epididymal tails that are small and firm, and infertility is often caused by their eventual obstruction.
Trauma
Trauma is a common cause of pathological changes in scrotal contents. As mentioned above, trauma often leads to the accumulation on fluid in the vaginal cavity in the form of a hematocele or hydrocele. Penetrating wounds of the scrotum can result in orchitis/periorchits with potential scrotal abscessation. Severe trauma can induce rupture of the tunica albuginea [10]. Leakage of sperm due to tubular damage of the testicle can invoke an autoimmune reaction leading to granulomatous reactions. Depending on the acuteness and severity of the trauma, significant scrotal enlargement and edema may be present (Figure 18.6).
Figure 18.6 Bull with acute bilateral scrotal enlargement secondary to trauma. Hemicastration was performed to remove a ruptured testicle.
Source: Image
