3.4.1. Intratesticular diseases
Testicular
neoplasms are the most common tumours of the genital tract of male dogs [
28,
34,
35,
36,
37,
38,
39] with a prevalence of up to 60% and an incidence that increases with age [
16,
40,
41,
42,
43] and cryptorchidism [
37,
38,
39,
40,
44,
45,
46].
The ultrasonographic features of testicular tumours are extremely variable [
16]. Testicular tumours can range from circumscribed small nodules (focal tumours) to large complex masses (diffuse tumours) with heterogeneous echo-pattern and disruption of normal anatomy. Sertoli cell tumours and seminomas are usually large with mixed echogenicity, resulting sometimes in generalized testicular enlargement, while interstitial cell tumours may appear as well-defined focal hypoechoic lesions [
28], but shape, margin and echogenicity do not allow differentiation between tumour types [
16].
Areas of haemorrhage and necrosis may occur in all tumour types and may be seen ultrasonographically as disorganized hyperechoic and hypoechoic regions, as areas of calcification within the testicular parenchyma could be seen, appearing as hyperechoic foci producing acoustic shadowing [
28].
Although testicular tumours showed a lesser ability to metastasize (<15%), early detection by ultrasonography allows the orchiectomy of the affected testis and improves the chance to maintain the fertility of the patient, especially in breeding dogs [
16].
There are few reports in which dogs had been diagnosed with neoplasms of testicular origin in an extra-testicular location [
47]. Few possibilities, including the presence of embryological ectopic tissue or the presence of testicular tissue transplanted during castration, are considered causal [
47]. The location of the extra-testicular testicular tumours in dogs is varied and includes the spermatic cord, the inside of the scrotal skin or the site of the pre-scrotal castration incision site [
47]. Most of the neoplasms were small and about 1.5 cm in diameter [
35]. Their appearance, apart from their location, is undistinguishable from their intratesticular counterpart [
35].
Orchitis, as the inflammation of the testis, could run acutely or chronically. Acute orchitis may have variable ultrasonographic characteristics, ranging from irregular and poorly defined anechoic areas to a diffuse patchy hypoechoic echo pattern, and focal abscessation may be evident [
15,
17,
30]. Usually, there is an enlargement of the testis and epididymis, and fluid may accumulate between the visceral and parietal tunic within the scrotum [
15,
17,
30,
48]. Chronic orchitis is less obvious regarding ultrasonography features and may reveal hyperechoic or mixed echogenic parenchyma, with a reduction in testicular size [
17]. Abscess can also occur as a chronic progression of the orchitis, and its feature is characterized by an irregular hyperechoic wall and anechoic to hypoechoic central contents [
17].
Torsion of the spermatic cord is uncommon in dogs [
17]. Depending on the degree of the torsion, due to the peculiar structure of testis vascularization, the consequence is the necrosis of the testis. It could be seen mainly in retained (or cryptorchid) testes [
35]. Moreover, torsion of the spermatic cord in the intra-abdominal testicle was frequently reported in the presence of testicular tumours [
15,
17,
44]. The ultrasonographic appearance of experimentally induced testicular torsion in the dog has been reported by Hricak et al.: from 15 to 60 minutes after torsion there are anatomical changes visible by ultrasound as a testicular enlargement characterized by diffusely decreased parenchymal echogenicity, and a concurrent enlargement of the epididymis and spermatic cord. The scrotal skin becomes hypoechoic and increases in thickness [
49].
Testicular hypoplasia is a developmental defect of the testis, which does not reach the post-pubertal normal size. Most cases of hypoplasia are because of cryptorchidism, and in several cases are linked to the inability of the epididymis to reach the normal size too [
35].
Differently from hypoplasia,
testicular atrophy is used to define normally developed testis that became smaller in size, as a result of ageing [
35], cryptorchidism, testicular tumour or chronic orchitis in the opposite testicle [
17]. An atrophic testis typically has a normal-sized epididymis, so proportions change with increased severity.
In both testicular hypoplasia and atrophy, at the ultrasonographic examination albuginea appeared thick, and vessels are less obvious or missing. The echotexture could be variable, hypoechoic to isoechoic, or also diffusely hyperechoic depending on the cause and severity [
17]. Hyperechoic foci producing acoustic shadowing could be present, reflecting parenchymal mineralization [
35].
Ultrasonography is also very useful in
cryptorchidism for locating and evaluating undescended testicle(s), which may be located in the abdominal cavity, inguinal canal, or in an ectopic subcutaneous location between the superficial inguinal ring and the scrotum [
50]. Cryptorchid testis is usually small in size, thus testicular parenchyma could be demonstrated by detecting the hyperechoic mediastinum.
3.4.2. Extratesticular diseases
Epididymitis can occur separately or concurrently with orchitis (
Figure 3), and the damage may extend to include the ductus deferens [
15,
17,
30]. Usually, epididymitis involves the tail and sometimes the body of the epididymis; the head of the epididymis is seldom involved [
51].
This may be bilateral or unilateral, and the severity varies and reflects the degree of damage, including necrosis and vascular changes. In severe acute disease, there is swelling and edema of the tail of the epididymis, with a relevant increase in size [
35] with or without fluid accumulation into the vaginal cavity. Ultrasonography, by the direct visualization of the altered organs, improves the differential diagnosis of the disease causing the scrotal increase in volume [
13,
17,
30,
51].
Ultrasonography could be particularly valuable in the presence of extra-testicular (around the testicle but within the vaginal tunic)
fluid accumulation. In this case, the fluid causes a scrotal enlargement, preventing the clinical discrimination between the structures involved. Types of extratesticular fluid accumulation are serum (hydrocele), blood (hematocele), pus (pyocele), or possibly urine [
11,
13].
Rarely
epidydimal cysts, fluid accumulation as the result of epididymal canal’s occlusion, were reported in dogs [
11].
Varicoceles in humans are caused by alterations in the veins of the pampiniform plexus where they become enlarged, elongated, and tortuous. On sonograms, varicoceles appear as an anechoic, tubular and serpiginous fluid collection in the region of the epididymis. Varicoceles are encountered rarely in dogs, and their ultrasonographic appearance has not been described [
11].