Discussion

Introduction:
As the population of older and geriatric horses increases, horses with genital tumours will present more frequently. In human medicine, a standardised approach to the diagnostic work-up and treatment of penile tumours exists.

Considerations:

The primary lesion. The size, location, mobility, extent of infiltration, tumour type and cellular differentiation of the primary lesion all affect the treatment options. In humans, a consensus on diagnosing and staging penile neoplasia was performed (Heyns et al. 2010). Physical examination of the penile lesion was considered mandatory. Additional information may be obtained by advanced imaging such as MRI. Histological diagnosis (preferably from an excised specimen) is also mandatory. Furthermore, the histopathology report should include information on all prognostic parameters including the tumour size, histologic type, growth pattern, depth of invasion, thickness, resection margins, and lymphovascular and perineural invasion all of which contribute to the tumour 'grade'.

Involvement of regional lymph nodes:
Generally, the first lymph nodes (LNs) to be affected in horses with penile tumours are the superficial inguinal LNs followed by the deep inguinal LNs and then the medial iliac LNs. Palpation to evaluate for enlargement of these LNs is indicated in any horse with a penile mass; however, this is an insensitive method of detection of LN involvement. In humans with penile tumours, physical examination of the inguinal and pelvic areas is mandatory and ultrasound-guided fine needle aspiration (FNA) cytology of inguinal LNs is recommended. Humans considered at high risk for inguinal LN metastasis may undergo dynamic sentinel node biopsy or even a (modified) LN dissection even if a FNA is normal.

Distant metastasis:
Equine penile/preputial squamous cell carcinomas have metastasised to the lungs, liver, myocardium, thoracic verterbrae and abdomen. In humans with penile tumours and metastases confirmed in the inguinal LNs, it is indicated to perform CT to evaluate for iliac LN metastasis. If the pelvic CT findings are positive, it is indicated to evaluate the remainder of the abdomen and the thorax.

Other treatment considerations:
In veterinary medicine, it is also essential to consider and discuss the cost of the treatment as well as the secondary effects of the treatment.

Surgical treatment options:
In human medicine, a multidisciplinary approach integrating chemotherapy, surgery and radiation therapy is the mainstay of modern treatments for neoplasia. Although this abstract focuses on surgical treatment for penile neoplasia, the importance of a multimodality approach cannot be overemphasised.

Cryosurgery:
Technique: Two to three freeze (-20 degrees C) thaw cycles to form intracellular ice crystals, disturb electrolyte and fluid balance, denature cell membranes and cause thermal shock. Cryosurgery may cause a delayed antibody and cell mediated immunity which possibly contributes to resolution of tumours distant to the cryosurgical site.
Use: Small and superficial tumours or in combination with surgical
debridement. Cryosurgery is not curative for horses with invasive tumours or LN metastasis.

Simple excision:
Technique: The tumour and a margin of grossly unaffected tissue are sharply excised. In man, low-grade tumours should have a 10 mm margin and high-grade tumours should have a 15 mm margin. Use: Small solitary lesions on the penis or prepuce without involvement of the tunics, cavernosa, urethra or LNs.

Segmental posthioplasty/posthectomy, reefing:
Technique: Two parallel circumferential incisions are made and the cylinder of tissue containing the tumour(s) is removed before suturing the defect.
Use: Small - medium solitary or multiple small penile tumours that
are too extensive for simple resection. Tumours should not involve the tunics, cavernosa, urethra or LNs or extend beyond the dermis.

Laser excision:
Technique: Laser excision is an alternative to simple excision and has the potential advantages of a bloodless surgical field, decreased risk of spread of tumour emboli and decreased post operative pain and swelling. At least 1mm of 'normal' tissue should be vaporised on the periphery of the lesion; latent thermal necrosis increases the margin of tissue death beyond that incised at surgery.
Use: As for simple excision.

Partial phallectomy:
Technique: After preparation, the penis is incised to the urethra, haemostasis is attained (the corpus cavernosum and spongiosum are closed and the dorsal penile vessels are ligated) and the penile urethra is sutured to the penile epithelium in a method that prevents stricture formation.
Use: Penile tumours located on the glans penis or free portion of
the shaft that are too extensive for local excision alone. Partial phallectomy is not recommended if the tumour goes beyond the annulus of the inner preputial fold or if there is LN or preputial involvement.

Partial phallectomy and sheath ablation:
Technique: An elliptical incision is made around the penis and prepuce and both are dissected free from the ventral abdomen. The inguinal lymph nodes may be resected. The prepuce and penis are resected proximal to the lesion, haemostasis is attained and the penile stump is secured to the ventral body wall. The urethra is sutured to the skin in a method that prevents stricture formation.



Use: Penile tumours confined to the distal aspect of the penis but that extend beyond the annulus of the inner preputial fold and tumours with concurrent or potential LN involvement.

En bloc penile and preputial resection with penile retroversion:
Technique: The penis and prepuce is dissected from the ventral abdomen as per the technique for partial phallectomy and sheath ablation. The inguinal lymph nodes, penis and prepuce are resected and haemostasis is attained. The penis is reflected caudally and the distal end is exteriorised through a second surgical incision ventral to the anus. The subcutaneous tissue is sutured to the tunica albuginea and the perineal skin is sutured to the urethral mucosa in a method that prevents stricture formation.
Uses: Horses that have extensive penile involvement, resection of
which precludes securing the penis to the ventral abdomen without urine scalding the hindlimbs, or horses with peripreputial skin involvement precluding preputial reconstruction, or tumours refractory to a previous conservative surgical approach.