By Dr Soo Kuan
What are anal sacs?
The anal sacs are two small pouches found near the anus in dogs and cats. They are lined with glandular cells, and can produce very smelly secretions. Their exact function is unknown though it may be involved with the fight and flight reflex (i.e. they express when the dog is frightened to dissuade enemies from attacking).
What are problems that can occur with anal sacs?
In many dogs, and in most cats, the anal sacs are rarely a cause for concern. However, there are two categories of conditions that can occur with anal sacs:
- Infections – e.g. repeated infections and abscesses associated with their anal sacs, which cause them a great deal of pain and discomfort.
- Cancers – some dogs and cats may develop a cancer associated with their anal sac.
Anal sac infections are rarely life-threatening. However, your vet may recommend surgery to remove your pet’s anal sacs (anal sacculectomy) to treat their repeated infections. This is particularly important as repeated antibiotic use in the long term may increase the risk of development of antibiotic-resistant bacteria.
Anal sac cancers generally affect older patients, and usually present as a lump on the side of the anus. The most common cancer associated with the anal sac is an apocrine gland adenocarcinoma, or an anal sac adenocarcinoma. This cancer itself generally only causes a problem when it becomes large enough to interfere with defaecation. The cancer can also spread to the draining lymph nodes in the abdomen and this can also make defaecation difficult. The tumour can also cause increased calcium levels in the blood which can lead to kidney damage. Surgery for anal sac adenocarcinomas involves removal of the affected anal sac, as well as any enlarged lymph nodes. The long-term prognosis after surgery in most cases is good.
How are anal sacs conditions diagnosed?
Infections may be associated with swelling, but is usually painful or red, and may be associated with some discharge. They generally resolve with antibiotic creams or oral antibiotics.
Cancers generally affect older patients, and are rarely painful or red. They do not improve with antibiotics.
To make a diagnosis, a fine needle aspirate (where cells are collected via a needle) or a biopsy (where a piece of tissue is collected surgically) may need to be performed and submitted to the laboratory. Biopsies are inherently more accurate but are more invasive and require general anaesthetic.
What does anal sac surgery involve?
If anal sac cancer is confirmed, a CT scan is often recommended. The most common form of anal sac cancer (anal sac adenocarcinoma) often spreads to the draining lymph nodes in the abdomen. A CT scan is important to determine which lymph nodes are affected and determine whether they also need to be removed during surgery. As there is a risk of the cancer spreading elsewhere, organs like the liver and lungs also need to be checked.
If your pet is undergoing anal sacculectomy due to repeated infections, surgery will involve removal of one or both anal sacs. The skin is cut on either side, next to the anus, the anal sac(s) are removed, and the ducts tied off. Generally, internal dissolvable stitches are placed to close the wound.
If your pet is undergoing surgery to remove an anal sac adenocarcinoma, the surgery is similar, but generally only the affected sac is removed. Any enlarged lymph nodes are also removed from the abdomen – this incision is made on the underside of the abdomen.
What are the risks associated with anal sac surgery?
All surgeries carry some inherent risk of infection and wound complications. Additionally, if the nerve to the anal sphincter has been affected by the cancer, there is a very low risk of faecal incontinence
The abdominal lymph nodes are surrounded by major blood vessels so there is a risk of haemorrhage with their removal. However, this risk is very small with the highly trained team at SASH, including Surgery Specialists who have advanced training in soft tissue surgery. If bleeding does occur, we have a blood bank on site so that a blood transfusion is readily accessible.
Caring for dogs at home after anal sac surgery
At home, your pet will need to be kept quiet and confined for about 4 weeks. Dogs can be walked outside on a lead to toilet for 5 minutes, every 4-6 hours.
To help keep the stools soft, we recommend adding Metamucil or Coloxyl to their diet to soften the faeces. You will also need to give all medications, including antibiotics and anti-inflammatory medications, as prescribed.
Recovery after anal sac surgery
Most wounds should heal uneventfully within 2 weeks. If there are any wound complications, they can often be treated with additional medication and time, rather than needing additional surgery.
If your pet was being treated for repeated anal sac infections, once their wounds have healed and been assessed by a Surgeon, they should not need to return to SASH for any further treatments. However, if your pet was being treated for anal sac adenocarcinoma, our Oncologists (cancer specialists) may recommend that they receive chemotherapy once their wound has healed. This will be discussed with you after surgery and once the results of any pathology tests have returned.
If you have any concerns about your dog’s anal sac, please consult your local veterinarian. They may then refer you to a SASH vet who is Specialist in Surgery, or to the Animal Cancer Centre, if cancer is diagnosed.