Clinical Presentation And Description Of Clinical Diagnosis

Published Date: 02 Nov 2017

Case Title: "Ultrasound Diagnosis: Intra-Abdominal Torsion of a Non-Neoplastic Testicle in a Cryptorchid Dog" (Hecht et al., 2004)

Clinical presentation and description of clinical diagnosis

A 6 month old bilaterally cryptorchid male Boxer was presented in an emergency scenario with acute abdominal pain upon palpation. The owners reported that when they returned after leaving it alone for six hours it was reluctant to stand and cried when they picked it up. Radiographs were taken and no abnormalities were found, and the dog's heart rate was elevated to 162bpm. (Hecht et al., 2004)

Ultrasound examination was undertaken and the left testicle was found to be hyperechoic and enlarged compared to the right, which confirmed the diagnosis of testicular torsion. Exploratory surgery found that the left testicle was haemorrhagic as the spermatic cord had rotated more than 360° in an anticlockwise direction, blocking venous return. Both testes were surgically removed and the dog made a full recovery. (Hecht et al., 2004)

Relevant anatomy

Anatomical overview of the male reproductive system

The reproductive system of the canine male consists of a pair of testes enclosed within peritoneum, fascia and skin. They are located between the hindlimbs, ventral to the rectum. The testes produce sperm and hormones. Sperm is transported via the epididymis and ductus deferens to the prostate gland, where it is mixed with seminal fluid. In the dog, the prostate is large, encasing the urethra. The urethra travels from the neck of the bladder, to the exterior of the penis, transporting semen and urine. The urethra is enclosed within the penis. The dog has a musculocavernous penis, composed of much erectile tissue, corpus cavernosum and corpus spongiosum. Distally, corpus cavernosum ossifies, forming splanchnic bone: the os penis. Engorgement of the bulbus glandis occurs during copulatory lock in dogs. The penis is suspended beneath the abdomen, cranial to the testes, supported by a suspensory ligament, and housed within the prepuce; a continuation of the skin of the abdomen. (Dyce et al., 1996)C:\Users\Ellie\Desktop\Canine Testicle copy.jpg

Anatomy of the testes, scrotum & epididymis

Figure I

Diagram showing the different parts of the canine testicle. (Carrington et al., 2012)

1: Tunica Albugineal 2: Mediastinum; 3: Seminiferous Tubules; 4: Straight Tubules; 5: Rete Testis; 6: Efferent Ductules; 7: Ductus Deferens; 8: Head of the Epididymis; 9: Body of Epididymis; 10: Tail of Epididymis; 11: Pampiniform PlexusThe testes, the structure of which is shown in Figure I, are contained within the scrotum, obliquely arranged dorsocaudally with an average size of 3cm long, 2cm wide and 2cm thick. Divisions in the testes give rise to regions know as lobules which are defined by connective tissue called the septula testis, which contain blood vessels, lymphatics and nerves (Slatter, 2003). Articular supply to the testes is via the testicular artery which originated from the aorta at approximated the level of the forth lumbar vertebra, with the right testicular artery slightly more cranial to the left (Slatter, 2003).

The right and left testicular vein are responsible for venous return from the testes via the pampiniform plexus which is formed within the spermatic cord. The right testicular vein drains into the caudal vena cava whereas the left drains into the left renal vein. The pampiniform plexus is responsible for heat transfer in order to prevent over heating of the testicles enabling optimal conditions for spermatogenesis (Slatter, 2003). Innervation to the testes is in the form of postganglionic sympathetic fibres which originate between L3 and L5 at the lumbar ganglion (Slatter, 2003).

The testes are surrounded by many different layers, as shown in Figure II, and these layers reflect their developmental origin in the abdomen. The outermost layer is a thin layer of skin which is closely adhered to the smooth muscle layer called the tunica dartos. Elevation of the scrotum is caused when the tunica dartos contracts due to changes in temperature (Dyce et al., 2010). The next layer is a spermatic fascia which can be divided into the external and internal spermatic fascias. The external fascia lies more superficially and can be easily separated from the tunica dartos. The internal spermatic fascia lies more deeply and is a tough fibrous sheath. The internal and external spermatic fascias are connected by the scrotal ligament and this would have to be cut during a closed castration. The ligament of tail of the epididymis attaches the tail of the epididymis to the internal spermatic fascia (Fuller, 2013).

Figure II

Transverse section of testis showing the different layers.(Ellis, 2006)

1: Scrotal skin; 2: Tunica dartos; 3: Cremaster muscle; 4: External spermatic fascia; 5: Internal spermatic fascia; 6: Parietal layer of vaginal tunic; 7: Visceral layer of vaginal tunic; 8: Tunica albuginea

The testes are suspended by a mesentery called the mesorchium, through which the testicular vessels and nerves run, and are enveloped by a peritoneal vaginal tunic, which originates embryologically from the vaginal process. The visceral layer is firmly attached to the surface of the testes and cannot be separated while the parietal layer lies more superficially. The vaginal cavity between the two layers generally contains a small amount of serous fluid and is continuous with the peritoneal abdominal cavity. The visceral layer of the tunica vaginalis lies on top of a thick fibrous connective tissue capsule called the tunica albuginea. The main branches of the testicular artery and vein are within this capsule (Dyce et al., 2010).

The epididymis is located on the dorsolateral aspect of the testes and consists of a tightly coiled epididymal duct having 3 main regions; the head, body and tail. It is the head region which communicates directly with the testes, whereas the tail attaches to the caudal portion via the proper ligament (Slatter, 2003). Arterial blood flow to the epididymis is from the prostatic artery while venous drainage is via the pampiniform plexus. Innervation of the epididymis is supplied from the testicular plexus which interconnects with the abdominal, aortic and caudal mesenteric plexuses (Budras, 2007).

The embryological development and descent of the testes

The proliferation of coelomic epithelium and underlying mesenchyme causes the genital ridges to form medial to the mesonephros at the level of the hindgut (McGeady et al., 2006). During this process, from week four to week six of the development of the embryo, primordial germ cells found in the epiblast travel via the primitive streak, yolk sac and then alongside the wall of the hindgut until they reach the genital ridges. Primordial germ cells then enter the mesenchyme below the genital ridges to form the primary sex cords which link the mesonephric duct to the genital ridge (Wakley, 2013).

At week seven, differentiation between the sexes occurs. In the male, sertoli cells produce a paramesonephric inhibitory hormone that causes the paramesonephric duct to disintegrate. Differentiated interstitial cells called Leydig cells in the genital ridge produce testosterone to initiate the formation of the ductus deferens, epididymis and seminal vesicle of the testicle (McGeady et al., 2006).

In the dog the testicles descend at around three to twenty five days post-natally depending on breed and size (McGeady et al., 2006). This is shown in Figure III. The gubernaculum links the testicle to the tail of the epididymis and the gubernaculum then continues through the inguinal canal until it terminates within the abdominal wall (Pasquini et al., 2007). The termination of the gubernaculum is bulbous and surrounded by visceral and parietal peritoneum (McGeady et al., 2006). The testis, along with the epididymis, moves caudoventrally through the inguinal canal following the gubernaculum until it terminates in the scrotum. After passing through the inguinal canal, the testicle has two peritoneal layers known as the visceral and parietal vaginal tunics as well as two more layers known as the internal and external spermatic fascias. The gubernaculum now reduces in size to become the proper ligament of the testicle, the ligament of the tail of the epididymis and the scrotal ligament (Pasquini et al., 2007).howard.jpg

Figure III

Descent of the testes in the dog. (McGeady et al., 2006)

1: Testis; 2: Gubernaculum; 3:ScrotumThe anatomy and pathology of the cryptorchidism and torsion described in the case

Cryptorchidism is a developmental disorder defined as the failure for one of both testes to completely descend into the scrotum. Different cases present with different levels of descent, so the undescended testis can be found anywhere between the kidney and the external inguinal ring (Wikivet, 2011). The specific origins of the disease are not yet clear but it may be caused by an autosomal recessive trait. Some breeds are more prone to the disease than others, Boxers included, with Poodles having the greatest incidence (Wikivet, 2011; Hecht et al., 2004). testes.JPG

Figure IV

Photograph from the clinical case of the two testes after surgical removal: the left testicle is swollen and filled with blood after torsion. (Hecht et al., 2004)Torsion refers to the twisting of the testicle, and is rare in dogs with descended testicles but those with undescended testicles, such as the Boxer in the case, are much more at risk (Hecht et al., 2004). Twisting of the testicular veins means that venous return is stopped, causing the testicle to fill with blood and become enlarged (Davol, 2001). This was observed in the clinical case, when a difference in echogenicity between the two testes was seen during ultrasound examination and the change in size and colour of the affected testis was observed compared with the unaffected testis upon surgical removal, as shown in Figure IV (Hecht et al., 2004).

Conclusion

In this clinical case, a developmental abnormality caused an atypical anatomical presentation which put the affected dog at a significantly greater risk of developing the condition discussed. Ultrasound diagnosis confirmed a case of testicular torsion and surgical removal of both testes meant that the dog recovered well.