Perianal tumors are a common occurrence in dogs and cats, originating from different glandular tissues in the perianal area. Understanding the types of tumors and their characteristics is essential for effective treatment and management. This article delves into the intricacies of perianal tumors, shedding light on their origins, diagnostic methods, and treatment options.
The Two Main Groups of Perianal Tumors
In dogs, perianal tumors typically arise from two main groups of glands:
- Apocrine Anal Sac Glands
- Perianal or Circumanal Glands (also known as hepatoid glands)
From these glands, both benign (adenoma) and malignant (adenocarcinoma) tumors can develop. Additionally, other types of skin tumors, such as mast cell tumors, melanoma, or lymphoma, can also be found in this area.
Anal Sac Gland Neoplasia: A Common Affliction
Tumors originating from the apocrine glands of the anal sac wall, known as adenocarcinoma of the anal sac, are quite prevalent in dogs. This type of tumor represents approximately 2% of all canine skin tumors. Certain breeds, such as Spaniels, Dachshunds, and Shepherd dogs, are predisposed to this condition. Recent studies have also highlighted genetic factors in English Cocker Spaniels (Polton, 2009).
The average age of dogs affected by anal sac adenocarcinoma is 11 years, and the occurrence is not significantly biased towards either gender. Interestingly, the assumption that anal sac tumors occur independently of hormonal status has been confirmed, as approximately 2/3 of affected animals in a recent study were castrated (Polton et al., 2006). Nevertheless, anal sac adenomas are extremely rare.
Symptoms of adenocarcinoma include the presence of circumscribed or infiltrative masses, which can range in diameter from 0.2 to 10 cm. Small tumors are usually detected through careful rectal palpation, while larger tumors may cause a visible perianal bulging mass or swelling. In extreme cases, the tumor can become enormous, leading to compression of the rectum, resulting in constipation and tenesmus.
The behavior of anal sac adenocarcinoma is marked by invasive growth, a typical pattern of metastasis, and the occurrence of paraneoplastic hypercalcemia. Metastasis to the regional lymph nodes is quite common and occurs rapidly. In fact, up to 75% of cases already have metastases at the time of diagnosis. Metastases can exceed the size of the primary tumor by far. Systemic metastasis to the lungs and abdominal organs occurs in later stages, with a rate ranging from 50% to 90% in different studies.
Hypercalcemia, the most common paraneoplastic syndrome associated with anal sac adenocarcinoma, affects 30-50% of cases. This condition is characterized by elevated blood calcium levels, resulting in symptoms such as increased urination and thirst, lethargy, loss of appetite, weight loss, weakness, bradycardia, vomiting, and constipation. The high blood calcium levels affect the kidneys, smooth and striated muscles, and the central nervous system.
Cytology is usually sufficient for a definitive diagnosis, and careful staging through various examinations is essential for forming an effective treatment plan. Treatment typically involves surgical removal of the tumor, followed by irradiation and/or chemotherapy. A segmental resection of the anal sphincter is often necessary but can result in partial or complete fecal incontinence, particularly with more extensive resections.
Tumors of the Circumanal Glands: The Hepatoid Glands
The hepatoid glands, also known as perianal or circumanal glands, are scattered throughout the perianal area in dogs. They can also be found in other regions of the body, such as the base of the tail, vulva, prepuce, hind legs, and caudal dorsum. While their exact purpose is unknown, these glands are regulated by sexual hormones and contain androgen receptors.
Tumors originating from the circumanal glands are among the most common neoplasias in dogs, with benign adenomas accounting for the majority (81-96%) of cases. Perianal gland carcinomas are less prevalent. Intact male dogs are more prone to developing perianal adenomas, while castrated female dogs have a higher incidence. Generally, older dogs are affected, with predispositions observed in breeds like the Cocker Spaniel and Fox Terrier. Testicular tumors are often present alongside perianal adenomas.
Histologically, perianal adenomas typically exhibit a lobular architecture, occasionally displaying regions with distinct cellular pleomorphism. Some pathologists recognize an intermediately differentiated group of adenomas, which can also be identified clinically as a more invasive subtype.
Clinical signs of perianal adenomas include the presence of solitary or multiple masses in the perianal or preputial area, which can become ulcerated and infected. The characteristic appearance of these tumors enables their easy recognition. Malignant forms can resemble adenomas, but they tend to be more infiltrative and have a more aggressive clinical appearance. The course of the disease can last up to a year. Cytology may not always definitively differentiate between adenomas and carcinomas due to the pleomorphic nature of even benign adenomas.
A digital rectal examination is necessary to assess the degree of invasion, palpate the prostate, and examine the sublumbar lymph nodes. The testicles should also be examined. Additional diagnostic measures, such as sonography and radiographs, are essential for assessing metastasis and the extent of the disease. Lymph nodes and lungs are the most common sites of metastasis.
In the case of small and nonulcerated tumors in intact males, castration is the recommended treatment. Surgical resection is indicated for ulcerated or bleeding tumors, recurrence cases, and in female dogs. Without castration, tumor recurrence or the development of new tumors is likely. Surgery often leads to regression or non-progression of small tumors. Radiation therapy is effective for adenomas, with a remission duration of over a year observed in nearly 70% of dogs. However, it is primarily used for stud dogs. With castration and tumor removal, the prognosis for perianal adenomas is favorable, with recurrence rates below 10%. In cases of recurrence despite castration, a second biopsy to rule out carcinoma is strongly advised.
Carcinomas of the circumanal glands do not respond to castration alone. Wide surgical resection is recommended, and prognosis depends on the stage of the disease. Dogs with low invasive tumors of less than 5 cm diameter and no metastasis have a good prognosis, as long as wide surgical resection is feasible. In cases where surgery is not possible, radiation therapy of the tumor site and the sublumbar lymph nodes is recommended. Survival rates of longer than one year have been observed in 47% of dogs treated with primary or adjuvant radiation therapy (Vail et al., 1990).
Tumors of the Anal Sacs in Cats: A Rare Occurrence
While anal sac carcinomas are rare in cats, they have been reported in isolated cases. Female cats and Siamese cats are predisposed to this condition. Clinical symptoms usually include dyschezia, constipation, and changes in fecal diameter. The perianal mass is often ulcerated and can initially be mistaken for an abscess. Most tumors have a diameter of less than 2 cm. Metastasis to the sublumbar lymph nodes, lungs, and other organs has been reported, although the frequency has not been extensively studied. Hypercalcemia appears to be uncommon.
Whenever possible, surgical resection is recommended as the primary treatment option for anal sac carcinomas in cats. The success of chemotherapy in these cases is unknown, with only a single case report describing a partial remission following Carboplatin chemotherapy. The one-year survival rate for cats with anal sac carcinomas is 19%, and the median survival time is approximately 3 months (Shoieb et al., 2009).
Adequate treatment and management of perianal tumors in dogs and cats rely on understanding the specific characteristics and requirements of each case. Early detection, accurate diagnosis, and appropriate therapeutic interventions can significantly improve the prognosis and quality of life for affected animals.
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