Introduction

Among the skin neoplasias of epithelial origin in dogs, those related to perianal gland (also called hepatoid gland or circumanal gland) represent 28% of tumors, from this total, 27% correspond to adenomas and epitheliomas and only 1% to carcinomas (Souza 2005). Those are the most common neoplasias in male dogs and occur less frequently in females (Henderson & Brewer 1998). The development of benign tumors of the perianal gland appears to be hormone-dependent, with androgen stimulation (Withrow & Vail 2007). However, the perianal region may be affected by other neoplasias, but in lower frequencies than those that originate from the perianal gland, citing them: melanoma, lipoma, squamous cell carcinoma, leiomyoma, mast cell tumor (Souza 2005), soft tissue sarcomas and transmissible venereal tumor (Withrow & Vail 2007). Thus, any type of neoplasia can occur in the perianal region (Assunção et al. 2008). Despite some perianal tumors being asymptomatic, constipation and functional constipation are observed when these are large and invasive. The progressive increase of the formation or the excoriation of the skin on the perianal region, generally promotes bleeding (Matera et al. 2000). In some situations, even with histopathological examination, it is difficult to distinguish between benign and malignant tumor (Hedlund 2005). Surgical excision is the chosen treatment in cases of perianal neoplasias (Hedlund 2005). Due to the hormonal dependence of perianal adenomas, most of these regresses after castration and recurrence is uncommon (Withrow & Vail 2007). Some perianal tumors respond to chemotherapy or radiotherapy (Hedlund 2005). Other unconventional treatment options correspond to cryosurgery, hyperthermia, laser application with carbon dioxide (Assunção et al. 2008) and photodynamic therapy (Gouvêiz et al. 2005). The clinical, surgical and pathological studies become essential for perianal tumors in dogs, because of the variety of neoplasias (each with its biological behavior and individual therapeutic measures) that can affect this region. According to the above, this study aimed to evaluate the clinical features and microscopic classification of perianal neoplasias in dogs.

Materials and Methods

Six animals of the canine species, with distinction of sex, breed and age, had been evaluated during the years of 2007 and 2008. All patients had a record of tumor in the perianal region. The animals were submitted to general physical examination and macroscopic evaluation of the perianal neoformation. For the latter it were observed the following criteria: growth morphological patter, quantity, unilateral or bilateral location, consistency, erosion and/or area ulceration, diameter, impairment level of the anal sphincter and palpation of regional lymph nodes. Then, it was requested additional tests, such complete blood count, urea and creatinine serum evaluation, besides abdominal ultrasonography and perianal injury cytology. Because of the clinical and laboratory alterations, it was decided to perform the surgical excision of the patients neoformations, associated with bilateral gonadectomy. As pre-anesthetic medication, it was used acepromazine (0.05 mg/kg, intramuscularly) and tramadol (2 mg/kg, intramuscularly). Anesthetic induction was performed with propofol (5 mg/kg intravenously) and it was maintained with isoflurane and oxygen. The surgical technique was recommended by Assunção et al. (2008). After surgical resection, the neoformation of each animal was fixed in 10% formalin solution and sent to conventional histopathological analysis. For postoperative it was prescribed enrofloxacin (5 mg/kg), metronidazole (12.5 mg/kg), meloxicam (0.1mg/kg), tramadol (2 mg/kg). All drugs were administered orally. It was also recommended the cleaning of the surgical wound, on a daily basis, with triclosan liquid soap and use of the Elizabethan collar. The removal of the skin sutures was performed, on average, ten days after surgery. Data on the animals' age, tumor diameter and the impairment level of the anal sphincter were organized in the form of average. For other clinical parameters and microscopic findings, it was realized absolute and percentual frequency.

Results

From the six dogs tested, five (83.3%) were male and only one (16.7%) female. In regard to breeding distribution, three (50%) were Mixed Breed Animals, followed by one (16.7%) Poodle, one (16.7%) Pinscher and one (16.7%) Pit Bull. Ten years was the average patients' age. In regard to in situ macroscopic characteristics of the perianal neoformations, four (66.6%) animals exhibited a morphological pattern of pedunculated growth, while two (33.4%) showed a sessile growth. It was observed that in five (83.3%) cases the tumor was single. One (16.7%) dog presented multiple neoformations. The location was unilateral in five (83.3%) patients and only one (16.7%) showed bilateral location. Within six (100%) animals, the neoformations showed a firm-elastic consistence and ulcerated and/or necrotic area. At no time there was macroscopic change of regional lymph node. The tumors average diameter was 8.3 cm and the average impairment level of the anal sphincter by the injury equaled 107°. The hematology, serum biochemistry and abdominal ultrasonography revealed no changes worthy a note. In four (66.6%) cases, the cytologic findings suggested the presence of benign neoplasia of epithelial origin. The histopathological result in all these cases equaled to adenoma of the perianal gland. In one dog, cytology detected the occurrence of one (16.7%) mast cell tumor. However, the histopathological analysis of this was essential to define the microscopic staging of the neoplasia, demonstrating to be a moderately different mast cell tumor (grade two), with surgical margins not permeated by the neoplasia. The owner has not chosen to adopt chemotherapy as adjuvant therapy. In the only female dog in this study, the cytopathologic examination detected the occurrence of one (16.7%) transmissible venereal tumor, which was confirmed by histopathology. Later (after the withdrawal of the suture), the patient was submitted to monochemotherapy consisted of vincristine sulfate.

Discussion and Conclusions

The adenoma of the perianal gland comprehends more than 80% among the perianal tumors (Matera et al. 2000). Adenomas occur 12 times more in male intact dogs than in female intact dogs, although they are common in ovariohysterectomized bitches. They may be single or multiple and they usually are salient (Hedlund 2005). These tumors affect old dogs, between eight and thirteen years old (Souza 2005). The smaller neoplasias (less than one centimeter in diameter) are spherical or ovoid and tend to become ulcerated and multinodular as they get larger (until ten centimeters in diameter). The perianal neoplasias are usually firm, of dermoepidermal location and good to poorly circumscribed (Scott et al. 1996). The highest adenoma frequency in relation to other perianal neoplasias, its epidemiological characteristics and respective macroscopic changes agree with the observations of this work. Less commonly, the perianal tumors of glandular origin arise from the apocrine glands of the anal sac (Scott et al. 1996), the adenocarcinoma of the anal sac is a highlight. One of the clinical implications of such neoplasia is the secretion of a substance similar to parathyroid hormone, which raises the levels of serum calcium (causing the hypercalcemia paraneoplastic syndrome), and may cause soft tissue dystrophic calcification and renal failure (Henderson & Brewer in 1998). However, this histological type was not found in the cases examined in this study. This may explain the proper condition of the patients in the pre-operative (confirmed by the results of laboratory tests) as well as in postsurgical recovery. The cytological examination, to distinguish the biological behavior of benign or malignant tumors of perianal tissue, may be of little compensation (Withrow & Vail 2007). However, it was found in a surgical-clinical study of canine perianal neoplasias, a positive correlation between the cytologic and histopathologic examinations' results (Assunção et al. 2008). This last quotation is in concordance with the cases evaluated in this study. Despite the need for microscopic examination to establish the diagnosis, the anatomopathological difference between adenoma and adenocarcinoma is difficult and not always precise (Matera et al. 2000). The canine transmissible venereal tumor is a round cell neoplasia of natural occurrence and it is located mainly in the mucosa of animals' external genitalia from both sexes, although there are also reports of extra genital occurrences, as in the oral and nasal cavity, ocular conjunctiva, tonsil, skin, anal and perianal regions. This neoplasia occurs by the deployment of viable tumor cells in the mucous membranes during mating (by means of scratches, licking, biting) or by smelling the animal (Varaschin et al. 2001). The occurrence of perianal transmissible venereal tumor in the only examined bitch could be justified by attempts wrong mating by the male holder of the neoplasia, since the female had no injuries in the vulva and/or vagina region. The mast cell tumor ranges from floating to firm skin lesions, papular to nodular, pedunculate to vegetative, of skin coverage or subcutaneous and good to poorly circumscribed, mimicking any cutaneous neoplasia. The lesions diameter varies from a few millimeters to more than 30 centimeters. Its etiology is unknown and probably multifactorial. The age of onset is eight and a half years and there is no gender preference for the development of the neoplasia (Rocha et al. 2004). Approximately 50% of the cases occur in the perianal region and trunk. The mast cell tumors with perianal location are associated with more aggressive behavior, but recent studies suggest no difference between the perianal/inguinal mast cell tumors with other skin sites (Withrow & Vail 2007). This quote confirms the mast cell tumor evaluated, even if the location is perianal and not being held adjuvant chemotherapy, there was no recurrence of the injury. Although the transmissible venereal tumor and mast cell tumor are not demonstrably hormone dependent, the implementation of ovariectomy in the patient affected by the transmissible venereal tumor has preventive effect of future estrus and consequently reducing the possibility of tumor cells transplantation. For the mast, the orchiectomy was important to avoid the occurrence of neoplasia in the testicles and scrotum. Some of the tumors evaluated showed considerable diameter and impairment of the anal sphincter. However, the unilateral position of the majority, use of the appropriate surgical technique and other methods, such as orchiectomy in patients with adenoma, chemotherapy of transmissible venereal tumor and surgical margins free of damage to the mast cell tumor, were important factors that influenced positively the prognosis. The knowledge of certain perianal tumors histopathological types and its clinical presentation can be the basis for a therapeutic approach for subsequent canine patients that hold such disease.

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