Anal Sac Tumours

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Anal sacs are located on either side of the anal opening in dogs, cats and many other animals. A strong smelling fluid is usually secreted from the anal sacs during defaecation. The purpose of this secretion is thought to be associated with communication and territory marking. Anal sacs can become inflamed, infected or impacted. If this is the case you may notice your pet scooting their bottom along the ground and licking and chewing at the area.

Unfortunately an anal sac may develop a tumour, the most common of which is the Apocrine Gland Adenocarcinoma. Rarely both anal sacs can develop tumours simultaneously. Anal sac tumours can occur in both male and female dogs and can occur in any breed however they are more common in spaniel breeds. Anal sac tumours are very rarely seen in cats.

Signs and Symptoms:

The tumour may be seen as an external swelling in the perianal region however this is not always noticed if the tumour is small. You may notice that your pet is constipated or is straining to defaecate if the tumour is large and pushing on the rectal wall causing an obstruction.

Occasionally there may be no obvious signs or symptoms but the mass is felt during a routine rectal examination by your veterinary surgeon.


A fine needle aspiration biopsy (FNA – a small needle is inserted into the swelling to obtain a sample of cells) may be carried out to confirm the diagnosis of tumour.

Anal sac tumours have a high incidence of metastasis (spread to other areas) and so it is important to check for this occurrence. This is done by taking a chest x-rays to evaluate the lungs and an abdominal ultrasound to assess organs such as the liver and kidneys and to check for enlarged lymph nodes (most commonly the subiliac lymph nodes). Hypercalceamia (a raised blood calcium level) can be seen in approximately 25% of cases and so blood tests are important to check for this and to assess overall health of the patient.


Treatment options depend on several factors including the size of the primary tumour, presence of metastasis (spread) and general health of the patient. Spread of the cancer is usually seen as enlarged abdominal lymph nodes and can be seen in up to 50% of cases when first presented.

Surgery to remove the anal sac tumour and any enlarged lymph nodes is the treatment of choice for most cases. Occasionally due to the size of the anal sac tumour or the size of the enlarged lymph nodes surgery may not be feasible. Radiation therapy and chemotherapy can occasionally be indicated.

After surgery monitoring with clinical examination and ultrasound is recommended to check for recurrent disease or further spread of the cancer.

In many cases with appropriate treatment patients can have a normal quality of life for a prolonged period.

Aftercare and Prognosis:

All surgeries carry some degree of risk. This can be minimised by having an experienced surgeon perform the procedure. 

Following surgery your pet may be required to wear a protective collar (Elizabethan or comfy collar) to prevent wound interference which can introduce infection or cause problems with healing. Exercise is restricted for approximately 2 weeks to allow for recovery and wound healing.

Possible complications include infection and breakdown of the surgical wound. Occasionally faecal incontinence may occur if both anal sacs are affected and removed.

The prognosis following the diagnosis of an anal sac tumour does depend on various factors including the size of the mass, presence of spread and the treatment plan. As with many tumours early detection and intervention can greatly improve survival.