Michael H. Goldschmidt, MSc, BVMS, MRCVS, Diplomate ACVP Professor and Head, Laboratory of Pathology and Toxicology Chief, Surgical Pathology Department of Pathobiology
Frances S. Shofer, PhD, Adjunct Associate Professor of Epidemiology and Biostatistics
The anal sacs in the dog are paired structures found on the ventrolateral aspect of the anus. They are located between the external and internal anal sphincter muscles. The normal anal sac is between 0.5cm to 1.0cm in diameter. There is a short excretory duct that lies between the anal sac and the glabrous skin of the anal area. The anal sac and the duct are both lined by keratinizing stratified squamous epithelium. Several large sebaceous glands lie at the opening of the duct into the anal sac. In the wall of the anal sac are many apocrine glands which communicate with the anal sac via a duct. The anal sac contents contain desquamated keratin, as well as sebaceous and apocrine secretions. Anal sac gland tumors arise from the apocrine glands. It is important to note that these tumors are of apocrine and NOT hepatoid or perianal glands, which are also found in this area.
Definition: a benign tumor arising within the wall of the anal sac with differentiation to apocrine secretory epithelium
Synonyms: adenoma of the apocrine glands of the anal sac, perianal adenoma of the apocrine gland
This benign tumor is very rare. It cannot be differentiated on gross appearance from the malignant anal sac carcinoma. On histopathology, the tumor is well demarcated, has little cellular pleomorphism, a low mitotic activity, and consists of multiple small islands of glandular tissue which are separated by fibrovascular connective tissue.
Definition: a simple malignant tumor arising in the wall of the anal sac with differentiation to apocrine secretory epithelium
Synonyms: carcinoma of the apocrine glands of the anal sac, anal sac gland adenocarcinoma, adenocarcinoma of the apocrine gland of the anal sac, perirectal adenocarcinoma
|Female Spayed||342||33% (33%)|
|Male Castrated||361||35% (21%)|
|(Normal Population %)|
| Breeds at
|English Cocker Spaniel||14||<0.0001||8.7||5.1||14.8|
|English Springer Spaniel||38||<0.0001||2.4||1.7||3.3|
| Breeds at
|West Highland White Terrier||1||0.0011||0.10||0.01||0.71|
There are three different histopathological patterns found with this tumor.
Anal sac gland carcinomas can present in any one of the three forms listed above. Some carcinomas may actually contain different combinations of the cell patterns.
Anal sac gland carcinomas often metastasize via the lymphatics to the sub lumbar and sacral lymph nodes. Occasionally wide dissemination or metastasis to the lung and spleen may also be seen.