Small or large peri-anal nodules with or without ulceration, secondary infection and hemorrhage, necrosis and fragmentation.
Peri-anal adenocarcinomas :
Mass noted.
Dyschezia, anal pain.
Stranguria, dysuria.
Anal sac carcinomas :
Small or large masses in the anal sac region/perineum and pelvis.
Polydipsia/polyuria, weakness and lethargy (hypercalcemia).
Dyschezia, especially from enlarged sublumbar LNs.
Stranguria, dysuria.
Clinical signs
Peri-anal adenomas :
Small, discrete perianal nodules.
Large rapidly-growing peri-anal nodules with or without ulceration, secondary infection and hemorrhage, necrosis and fragmentation.
Prediliction sites peri-anal, preputial and tail skin but may be as far forward as neck.
Peri-anal adenocarcinomas :
Dyschezia and severe anal pain.
Enlarged sublumbar lymph nodes if metastasized.
Anal sac carcinomas :
Small, discrete nodules in the anal sac region.
Large masses diffusely infiltrating the perineum and pelvis.
Enlarged sublumbar lymph nodes if metastasized.
Diagnostic investigation
Radiography
Thoracic radiographs for identification of pulmonary metastasis.
Abdominal radiographs for sublumbar lymph node enlargement.
2-D Ultrasonography
Ultrasound for sublumbar LNs more sensitive.
Biochemistry
Hypercalcemia (anal sac adenocarcinoma).
Histopathology
Biopsy from mass or excisional sample for definitive diagnosis.
Cytopathology
Fine needle aspirate from mass or enlarged lymph nodes may provide diagnosis.
Confirmation of diagnosis Discriminatory diagnostic features
History.
Signs.
Radiography.
Biochemistry.
Definitive diagnostic features
Histopathology.
Clinical findings.
Histopathology findings
Proliferating lobules of hepatoid gland: regular and mature cells in benign form; mitoses rare except in malignant form; less well-differeniated cells in carcinoma. Histological differentiation of adenomas from adenocarcinomas is considered to be difficult but their pattern of growth is usually helpful since the malignant form tends to be less discrete and more locally infiltrative.
Surgical removal (70% non-recurrence after 1 year) and castration (95% of non-ulcerated benign hyperplasias/tumors).
Radiation to local peri-anal site and LNs can help control.
Will have colitis/proctitis during treatment.
Benefit of chemotherapy is unknown.
Radiation therapy (local cure in at least two-thirds of irradiated tumors. However, the benefits of this approach over surgical management are doubtful).
Hormonal therapy (estrogen and delmadinone ). Peri-anal adenomas may become refractory to medical mangement; because of this and the risk of side-effects of long-term estrogen therapy, eg aplastic anemia, thrombocytopenia, surgical treatment is preferred.
Adenocarcinoma
Surgical excision if caught early, good prognosis. Resection may be difficult because of diffuse and infiltrative growth, and excision does little to halt metastatic spread, but this spread may take years to be seen.
Radiation therapy (see multi-element).
Chemotherapy .
Anal sac adenocarcinoma
Surgical excision. Very difficult to achieve wide local excision without causing anal sphincter dysfunction.
Also, sublumbar LN's often involved - can debulk.
Chemotherapy .
Subsequent management
Monitoring
Re-examination for recurrence.
Serial radiography, ultrasound for detection of metastatic disease.
Hematological monitoring if receiving chemotherapy.
Ross J T, Scavelli T D et al(1991) Adenocarcinoma of the apocrine glands of the anal sac in dogs - a review of 32 cases.JAAHA27 , 349-355.
Vail D M, Withrow S J et al(1990) Perianal adenocarcinoma in the canine male - a retrospective study of 41 cases.JAAHA26 , 329-334.
Dow S W, Olson P N et al(1988) Perianal adenomas and hypertestosteronemia in a spayed bitch with pituitary-dependent hyperadrenocorticism.JAVMA192 (10), 1439-1441.
Vetstream contributor(s)
Dr Laura Garrett DVM DipACVIM , School of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606, USA.
Histological differentiation of adenomas from adenocarcinomas is considered to be difficult but their pattern of growth is usually helpful since the malignant form tends to be less discrete and more locally infiltrative.