This page is part of the site called Surgical Pathology of the Canine Male Reproductive Tract by

Dr Rob Foster
OVC Pathobiology
University of Guelph

Disease of the Scrotal Skin and Vaginal Tunics

Table of Contents

Disease of the scrotal skin

Disease of the vaginal tunics and testicular tunic

Disease of the scrotal skin

 It has been often said that scrotal skin reacts just like the skin elsewhere, so it is not ‘special’. This is true, or at least is considered so. There is little point listing all the diseases of skin. Instead, the diseases that only affect scrotal skin, or have a predilectin for scrotal skin will be mentioned.

There is an extensive review of diseases of the scrotum (Cerundolo R, Maiolino P. 2002) and some of the conditions listed here are from that report.

Scrotal hyperplasia

The size of the scrotum of dogs is reported to increase in size, and become thickened with age. This thickening is reported to be hairless and to be deeply pigmented and wrinkled. Histologically the epithelium is hyperplastic and hyperkeratotic, and there is increased connective tissue (Bloom 1954).

Bloom F (1954). "Pathology of the Dog and Cat: The genitourinary system, with clinical considerations" Am. Vet. Publ Evanston, Illinois p258-259.

Masses (including neoplasms)

One may expect any neoplasm of skin to affect this region. Likewise, non neoplastic lesions would surely occur. Here are some examples of lesions that can occur

Mast cell tumour
Haemangioma/vascular hamartoma
Soft tissue sarcoma
Benign melanoma/melanocytoma
Malignant melanoma
Sebaceous carcinoma
Squamous cell carcinoma
Fibroadnexal hamartoma
Infundibular cysts
Skin tag

Trappler et al (2014) published a large study of scrotal tumors and this was the prevalence data based on laboratory submissions. There were 676 tumors from 655 dogs

Diagnosis Number
Round cell neoplasms 396
Mesenchymal neoplasms 92
Melanocytic 80


Epithelial neoplasms

Cysts and others 27

The round cell tumors were mast cell tumor (369) and histiocytoma (23). Mesenchymal tumors were hemangiosarcoma (34) and hemangioma (31). Melanocytoma (48) and malignant melanoma (32)


Trappler MC, Popovitch CA, Goldschmidt MH, Goldschmidt KH, Risbon RE. Scrotal tumors in dogs: a retrospective study of 676 cases (1986-2010). Can Vet J. 2014; 55: 1229-1233.


Mast cell tumour

Mast cell tumours are very common on the scrotum. There is a general belief that they are more aggressive than elsewhere. publications by Cahalane et al (2004) and Sfiligoi et al (2005) suggests this may not be the case. The numbers are low so a good large study is required. Sampling the superficial inguinal lymph node seems like a good idea!

Trappler et al (2014) reported on prevalence data of 676 cases. They found 369 mast cell tumors (55%). The majority were low grade tumors. There was no followup data.


Cahalane AK1, Payne S, Barber LG, Duda LE, Henry CJ, Mauldin GE, Frimberger AE, Cotter SM, Moore AS.Prognostic factors for survival of dogs with inguinal and perineal mast cell tumors treated surgically with or without adjunctive treatment: 68 cases (1994-2002).J Am Vet Med Assoc. 2004 Aug 1;225(3):401-8.

Sfiligoi G, Rassnick KM, Scarlett JM, Northrup NC, Gieger TL. (2005) Outcome of dogs with mast cell tumors in the inguinal or perineal region versus other cutaneous locations: 124 cases (1990-2001). J Am Vet Med Assoc. 226(8):1368-1374.

Trappler MC, Popovitch CA, Goldschmidt MH, Goldschmidt KH, Risbon RE. Scrotal tumors in dogs: a retrospective study of 676 cases (1986-2010). Can Vet J. 2014 Jan;55(1):1229-33.


Haemangioma/vascular hamartoma/hemangiomatosis

Weipers and Jarret (1954) report on hemangiomas of the scrotum. They begin as pigmented areas that remain static, but some progress to a small plaque that may eventually ulcerate and hemorrhage. Histologically they are cavernous haemangiomas. Bloom(1954) describes scrotal varicoses in the dog that have a similar description.

Trappler et al (2014) reported on prevalence data of 676 cases. They found 46 vascular hamartomas and 31 hemangiomas). There was no followup data.


Bloom F (1954). "Pathology of the Dog and Cat: The genitourinary system, with clinical considerations" Am. Vet. Publ Evanston, Illinois p 259-260

Weipers WL, Jarret WFH. (1954) Haemangioma of the scrotum of dogs. Vet Rec 66: 106-108.


Trappler et al (2014) reported on prevalence data of 676 cases. They found 34 hemangiosarcomas (5%). . There was no followup data.


Trappler et al (2014) reported on prevalence data of 676 cases. They found 23 canine cutaneous histiocytoma (3%). The majority were low grade tumors. There was no followup data.


As anticipated, the numerous bundles of smooth muscle in the scrotal dermis will lead to the formation of neoplasia here.

Melanocytic tumors

Trappler et al (2014) reported on prevalence data of 676 cases. They found 48 melanocytomas (7%) and 31 malignant melanomas (5%). There was no followup data.

Scrotal dermatitis and non neoplastic disease

Physicochemical injury

Self trauma (mutilation)

Involvement of the scrotal skin can be secondary to intrascrotal disease, especially of the tunics (see below) and periorchitis.

Dogs with epididymitis can and will excessively lick the scrotum to the extent that there is dehiscence of the testis through the deep ulcer. The presence of spermatic granulomas is a similar inciting factor (mutilation due to spermatic granulomas (Althouse et al 1993).


Some dogs target the genital region when fighting and this cause severe injury, both to the scrotum and the scrotal contents.


Severe cold and freezing of the skin with frostbite would be expected in those individuals whose scrotum is exposed to the elements in regions of subzero temperatures.


Some dogs spend long lengths of time lying in the sun, and some do so lying on their backs, thus exposing the scrotum to direct sunlight. Actinic injury would the anticipated from this.

Algal infection

Protothecosis can involve the scrotum of the dog (Ginel et al 1997)..

Bacterial infection

Brucella canis, the causitive agent of canine brucellosis, causes epididymitis and self mutilation of the scrotum can result. As well, a pyogranulomatous dermatitis caused by B canis is reported (Dawkins et al 1982). Schoeb and Morton (1978) report on a dog that had an ulcer of the scrotum from which B canis was cultured.



Infection of scrotal wounds with the larvae (maggots) of flies is anticipated. Screw- worm fly would be one such example.

Cuterebra emasculator infestation can involve the scrotum.

Viruses and Ricketsias

Rocky Mountain spotted fever causes a vasculitis in dogs and this may involve the scrotum (Keenan et al 1977)

General dermatoses

Contact dermatitis

The sparsity of hair on the scrotum makes the likely contact between external irritants more likely, and so involvement of the scrotum alone in such a reaction is expected.

Trenti et al (2011) reported on 13 cases of suspected contact scrotal dermatitis. There are 2 types - allergic contact dermatitis and iritant contact dermatitis. Allergic contact dermatitis requires development of an immunological response to an allogen, but irritant type is, at least theoretically an immediate reaction. This is a disease that requires clinical techniques to identify as the pathology and histopathology can only be supportive - there is no pathonomonic lesions for confirmation. In this study, 10 had lesions of the scrotum only and the offending agents included floor detergents, bleach, cement, laundry detergent and plastic fabric.

The lesions incude primary changes of erythema and secondary changes of erosions, ulcers, crusts, hyperpigmentation, and depigmentation. No histology was reported.

Trenti D, Carlotti DN, Pin D, Bensignor E, Toulza O. (2011) Suspected contact scrotal dermatitis in the dog: a retrospective study of 13
cases (1987 to 2003). J Sml Anim Pract 2011, 52: 295-300

Reactive Histiocytosis

Moore (1984) lists the scrotum as a place particularly affected in dogs with systemic (reactive) histiocytosis. Palmeiro et al (2007) reports one case of scrotal involvement with reactive canine histiocytosis.


YagerBest Histovet cases

The Yager-Best Histovet database contains numerous diagnoses of scrotal dermatitis and a summary is provided below.

Table 1. Diagnosis of non neoplastic/nonproliferative scrotal disease

Contact dermatitis
Erythema multiforme
sterile pyogranuloma syndrome

Althouse GC, Evans LE, Hopkins SM. Episodic scrotal mutilation with concurrent bilateral sperm granuloma in a dog. J Am Vet Med Assoc 1993; 202: 776-778.

Cerundolo R, Maiolino P. Review cutaneous lesions of the canine scrotum.Vet Dermatol. 2002; 13: 63-76.

Dawkins BG, Machotka SV, Suchmann D, McLaughlin RM. Pyogranulomatous dermatitis associated with Brucella canis infection in a dog. J Am Vet Med Assoc. 1982; 181: 1432-1433.

Ginel PJ, Perez J, Molleda JM, Lucena R, Mozos E. Cutaneous protothecosis in a dog. Vet Rec 1997; 140: 651-653.

Keenan KP, Buhles WC Jr, Huxsoll DL, Williams RG, Hildebrandt PK. Studies on the pathogenesis of Rickettsia rickettsii in the dog: clinical and clinicopathologic changes of experimental infection. Am J Vet Res. 1977; 38: 851-856

Moore PF. Systemic histiocytosis of Bernese mountain dogs. Vet Pathol. 1984; 21: 554-563

Palmeiro BS, Morris DO, Goldschmidt MH, Mauldin EA. Cutaneous reactive histiocytosis in dogs: a retrospective evaluation of 32 cases Veterinary Dermatology 2007; 18: 332-340.

Schoeb TR, Morton R. Scrotal and testical changes in canine brucellosis: a case report. J Am Vet Med Assoc.1978; 172: 598-600.


Vaginal tunics (tunica vaginalis) and testicular capsule (tunica albuginea)

The tunics are continuous with the peritoneum, so they are affected by the same influences as the abdominal cavity. Disease of the tunics can originate from the abdomen, or from the scrotal sac itself.

Fluid accumulation


An accumulation of blood within the cavity of the vaginal tunics is haematocele. Local trauma is the most likely cause, but any disease or condition resulting in hemorrhage can be the cause.


An accumulation of fluid within the cavity of the vaginal tunic is hydrocele. This fluid is typically a transudate and identical to ascitic fluid. It will form for all the same reasons that ascites forms.

Hydrocele with fluid restricted to the scrotum is seen secondary to other conditions such as metastatic Sertoli cell tumors that obstructed vessels, and caused varicosities and hydrocele (McNeil and Weaver 1980).


Zeman et al (1988) report a dog that developed scrotal cestodiasis from infection with Mesocestoides sp. The dog had severe peritoneal cestodiasis that migrated to the scrotal cavity.

Bloom (1954) reports the infection of the scrotum of a dog with Cuterebra emasculator. He also reports scrotal myiasis in dogs.

Bloom F (1954) Pathology of the dog and cat - The genitourinary system, with clinical considerations. American Veterinary Publications, Inc, Evanston Illinois. p261.

Scrotal (inguinal) hernia

Herniation of abdominal contents through the inguinal ring cause a swelling or mass in the region of the spermatic cord. This occurs as a result of trauma (such as when the abdomen of the dog is run over by a vehicle. It is reported as a spontaneous event (Dorn 1978) - omental fat herniated through the inguinal ring and occluded the vessels of the spermatic cord.

Hayes et al (1985) reported 235 dogs with inguinal hernias. 24 could have been trauma related. Waters et al (1993) reported on 35 dogs with inguinal hernias of which 11 were males. The herniated tissue is often fat, but intestines can sometimes be trapped in the hernia.

Inflammation (periorchitis)

Periorchitis is inflammation around the testis and it involves the tunics. It can arise from extension of peritonitis, from penetrating injury to the scrotum, but most commonly, it arises from epididymitis. The dependent nature of the scrotal sac means that exudates tend to remain in the sac. Organisation and fibrosis of exudates, and granulation tissue formation leads to adhesions.

Allison N, McDonald RK, Guist SR, Bentinck-Smith J.Eumycotic mycetoma caused by Pseudallescheria boydii in a dog. J Am Vet Med Assoc. 1989; 194: 797-799


There are an infinite number of potential neoplasms that could possibly be found on the vaginal tunics, or extending into the cavity. Neoplasia is very rare, however.


There is one case of metastatic carcinoma of the vaginal tunics in the Yager-Best Histovet database (YB162821). The dog was a 10 year old Labrador. The appearance of the cells and the history suggested it may have been a transitional cell carcinoma. The neoplasm involved the tunics around the spermatic cord predominantly.

Figure 1: Carcinomatosis of vaginal tunics. There are multifocal coalescing white nodules over the vaginal tunics.


Patnaik and Liu (1975) reported on a leiomyoma of the vaginal tunic in a 13 yr old dog. It was reported to be benign. McEntee (1990) also reports seeing one case.

McEntee K (1990) Reproductive Pathology of Domestic Mammals. Academic Press p 298

Patnaik AK, Liu SK.Leiomyoma of the tunica vaginalis in a dog. Cornell Vet. 1975 Apr;65(2):228-31.


Cihak et al (1986) found a 13 year old dog with a mesothelioma of the vaginal tunic - it spread to the peritoneum.

Vascellari et al (2011) reports on a case of malignant mesothelioma of the left vaginal tunics in a dog. This dog also had nodules within the peritoneum and the mesentery. This mesothelialoma was in a reactive for cytokeratin (AE1/AE3), vimentin and HBME-1 (a mesothelial marker).

There are two mesotheliomas of the tunic in the Yager-Best Histovet database (YB10166, 144539). One was a 10 year old Bouvier and the other was a 6 year old Staffordshire terrier. There was no followup on either dog.

McEntee (1990) reports seeing 4 mesotheliomas of the tunics.

Figure :Mesothelioma of the vaginal tunics (YB144539)


Cihak RW, Roen DR, Klaassen J. (1986) Malignant mesothelioma of the tunica vaginalis in a dog. J Comp Pathol. 96(4):459-462.

Son NV, Chambers JK, Shiga T, Kishimoto TE, Kikuhara S, Saeki K, Fujiwara R, Tsuboi M, Nishimura R, Uchida K, Nakayama H. Sarcomatoid mesothelioma of tunica vaginalis testis in the right scrotum of a dog. J Vet Med Sci. 2018; 80: 1125-1128.

Vascellari M, Carminato A, Camali G, Melchiotti E, Mutinelli F. (2011) Malignant mesothelioma of the tunica vaginalis testis in a dog: histological and immunohistochemical characterization. J Vet Diagn Invest 2011, 23:135;139


There is one case of fibrosarcoma involving the vaginal tunic in the Yager-Best Histovet database (YB162010). No followup is available to provide the clinical outcome.

Figure 2: Fibrosarcoma of vaginal tunic.

Bloom F (1954) "Pathology of the Dog and Cat: The Genitourinary System, with clinical considerations" Amer Vet Publ Evanston, Illinois. p

Dorn AS. (1978) Spermatic cord occlusion in a dog.J Am Vet Med Assoc. 173(1):81

Hayes HM, Wilson GP, Pendergrass TW, Cox VS. (1985) Canine cryptorchidism and subsequent testicular neoplasia: case control study with epidemiologic update. Teratology 32: 51-56.

McEntee K (1990) Reproductive Pathology of Domestic Mammals. Academic press. p297.

McNeil PE, Weaver AD. (1980) Massive scrotal swelling in two unusual cases of canine Sertoli cell tumour. Vet Rec 106: 144-146.

Patnaik AK, Liu SK. (1975) Leiomyoma of the tunica vaginalis in a dog.

Cornell Vet. 65(2):228-31.


Waters DJ, Roy RG, Stone EA. (1993) A retrospective study of inguinal hernia in 35 dogs.Vet Surg. 22(1):44-49

Zeman DH, Cheney JM, Waldrup KA.1988 Scrotal cestodiasis in a dog. Cornell Vet 78(3):273-279.