Introduction

The canine scrotum is made up of two layers, the skin and the tunica dartos, and is a potential space divided into two compartments by a median septum. The dartos forms a lining to both halves of the scrotum and also contributes to the scrotal septum.¹ The scrotum contains the testes, the epididymides, the spermatic cords, and the cremaster muscles, which are extensions of the internal abdominal oblique muscle. The external pudendal artery is the main blood vessel that supplies the scrotum, and the veins run alongside the arteries.¹

The male canine urethra is divided into penile and pelvic components, with the pelvic component subdivided further into preprostatic and prostatic sections.¹ The penile component begins at the ischial arch, and it is surrounded by the corpus spongiosum for its entire length.² The urethra at the level of the scrotum is more distensible and of larger size when compared to the prescrotal urethra, its exposure is relatively straightforward, and it is surrounded by less cavernous tissue than the urethra in the perineal region.³ There are three main reasons why the scrotal region is recommended when performing a canine urethrostomy. First, the urethra is at its largest diameter at this location, and this same diameter is continued proximally. Second, anatomically, the urethra is most superficial at this location, providing less interference from the corpus cavernosum during surgical dissection leading to less hemorrhage. Third, the urethra is widest at this location, which provides for easier urethrocutaneous apposition.

Indications for Canine Scrotal Ablation

Scrotal ablation (SA) refers to the removal of scrotal tissue. It is a procedure that can be considered at the time of neutering in older male dogs that have a large amount of scrotal tissue. This excessive tissue may pose a risk for seroma or hematoma formation postoperatively, or its removal may simply be an aesthetic request by the owner. Common medical indications for SA include the treatment of scrotal tumors and when the tissue becomes traumatized.⁴ In a 2014 study that evaluated 676 canine scrotal tumors,⁵ the most common scrotal neoplasms identified included round cell neoplasms (58.6%), followed by mesenchymal neoplasms (13.6%), melanocytic neoplasms (11.8%), hamartomas (7%), epithelial neoplasms (4.3%), and cysts/tumor‐like lesions (4%). Mast cell tumors accounted for 54.6% (369/676) of all scrotal tumors. Utilization of the scrotum as a full‐thickness skin graft has also been reported.⁶

When a patient has pathology affecting only the scrotal skin, a complete workup is indicated. Accurate owner anamnesis may increase the suspicion of scrotal trauma. Conditions that may only affect the scrotal skin include Brucellosis, Babesiosis, contact dermatitis, Cuterebra, Erysipelothrix, frostbite, hyperandrogenism, protothecosis, Rocky Mountain spotted fever, excessive UV exposure (sunburn), and neoplasia.⁷ Diagnosis should be made based on a combination of cytologic evaluation (impression smears, fine needle aspirates), serologic testing, culture and susceptibility testing, as well as histopathology. The pattern of lesions may also aid in formulating differential diagnoses.⁷ When neoplasia is suspected, screening for underlying tumor metastasis is recommended in the form of aspiration of superficial inguinal lymph nodes in addition to diagnostic imaging (thoracic radiographs, abdominal ultrasound, or computed tomography). Epithelial, mesenchymal, or melanocytic tumors may arise from the scrotal skin.⁷ These include squamous cell carcinoma, adenocarcinoma, fibrosarcoma, myxoma, hemangioma, hemangiosarcoma, vascular hamartoma, plasmacytoma, histiocytoma, transmissible venereal tumor, malignant melanoma, and melanocytoma, with the most common tumor affecting the canine scrotum being mast cell tumor (MCTs).^5,7,8 MCTs affecting preputial, inguinal, and subungual sites have been suggested to have a more aggressive behavior,⁹ however, other studies have suggested scrotal and inguinal tumors may behave similarly to MCTs in other cutaneous locations.^10–12

Scrotal Ablation Procedure

When performing a SA, the patient is placed in dorsal recumbency, and the scrotum and surrounding fur are clipped (Figure 31.1a,b). Care should be used when clipping the scrotum to prevent iatrogenic trauma, and plucking of the fur may be less traumatic. The pelvic limbs should be allowed to abduct naturally at the level of the hip. This allows for the skin of the scrotum and inguinal region to be placed at a point of maximal tension if the patient were to sit splay‐legged. When SA is combined with a routine neuter and the testes are accessible, a testicular block using 2% lidocaine with 1 mg/kg injected into each testicle is recommended for local analgesia^13,14 (Figure 31.1c). The skin and scrotum are sterilely prepped with povidone‐iodine or 4% chlorhexidine and 70% isopropyl alcohol or sterile isotonic saline.¹⁵ The patient is then draped in a routine fashion (Figure 31.2).

For an elective castration combined with SA in a healthy patient, the base of the scrotum is marked with a sterile marking pen where the thin scrotal tissue meets the thicker inguinal tissue. A routine, pre‐scrotal castration is performed pushing each respective testicle up to the apex of the desired SA incision. Castration prior to ablation is preferred by the author, as the vascular supply to each teste is effectively dealt with minimizing the risk of damage to the spermatic cord when later dissecting through the scrotal tissues (Figure 31.3).

Following routine castration, forceps can be placed into the right and left scrotal pouches to elevate the skin and dartos, which are to be incised along the pre‐planned inked margin. This protects the underlying vascular pedicles and urethra during dissection (Figure 31.4).

Following the removal of the scrotal tissue, the underlying urethra is readily identifiable. The separate underlying fascial incisions can then be closed using an absorbable monofilament suture (Figure 31.5).

The deep subcutaneous tissue can be closed in a simple interrupted or simple continuous pattern followed by intradermal or external skin sutures (Figure 31.6a–c). The tension across the incision should be reassessed throughout the closure and at the end of the procedure with the patient undraped (Figure 31.6c). The patient is reassessed at two weeks postoperatively for appropriate tissue healing (Figure 31.7).

When severe pathology affects the scrotum in the intact patient (Figure 31.8a) or if the surgeon prefers this method for a standard SA, a more “outside‐in” approach is required, as the testes are not always able to be exteriorized. The surrounding skin is inked in an elliptical shape at the point of maximal tissue resection, and the skin, subcutaneous tissues, and tunica dartos are incised (Figure 31.8b). If the patient is intact, each spermatic cord is carefully isolated, and a routine castration is performed. Identification of the spermatic cord can be challenging in the face of underlying tissue inflammation. Gentle traction on the scrotum throughout dissection and blunt dissection with right‐angle forceps in parallel with the spermatic cord will aid in safe identification.