Leiomyoma in Dogs

Neoplasia or abnormal tissue growths are defined by the cells on which they grow, as well as whether they are benign or cancerous. Leiomyoma is a benign tumor that forms on involuntary smooth muscle cells. The digestive muscles along the walls of the stomach and intestine is the most common place, but leiomyoma can also sometimes be found in the uterus of female dogs. Like most tumors, it’s more common in older dogs, but it can occur at any age. It produces similar symptoms to the malignant cancer leiomyosarcoma, so it’s not always easy to tell the two apart upon diagnosis. With no metastasis, however, leiomyoma will not spread to other areas of the body. It is much less dangerous and most dogs will make a complete recovery after surgical removal.

Leiomyoma is the benign form of leiomyosarcoma. Veterinarians define it as a non-cancerous tumor which grows on the involuntary muscles of a dog’s gastrointestinal tract. Since it isn’t malignant, this tumor won’t spread to other areas of the body and it is rarely fatal.

It isn’t possible to tell whether a tumor is malignant or benign based on the symptoms. See your veterinarian immediately if you notice any of the following signs in your dog:

• Vomiting (often with blood)
• Weight loss
• Diarrhea
• Lethargy
• Abdominal pain or swelling
• Palpable mass
• Constipation
• Tenesmus (feeling an urge to clear the bowls often)
• Blood in the stool (hematochezia)
• Black tar-like stool with dried blood (melena)

Types 

There are many types of tumors that form on various cells in the GI tract. These are some of the most common types relevant to your dog’s diagnosis:

• Leiomyoma – a benign tumor that forms on smooth muscle cells.
• Leiomyosarcoma – a malignant tumor which forms on smooth muscle cells, the second most common type of GI cancer in dogs.
• Adenocarcinoma – a fast growing malignant tumor which forms on glandular tissue, the most common type of GI cancer in dogs.
• GISTs (GI Stroma Tumors) – a tumor which forms on the nervous system cells that control the involuntary muscles in the GI tract. It has sometimes been confused with leiomyoma and leiomyosarcoma. It may be either malignant or benign.

It’s not known what causes tumors to form in dogs. As with humans, there could be related hereditary or environmental factors, but these haven’t been studied conclusively in dogs. It’s also not known what causes a tumor to be malignant or benign. The risk of tumor formation increases with age.

The veterinarian will complete full blood and urine tests. Leiomyoma and leiomyosarcoma typically show signs of hypoglycemia, so this is often apparent in a blood test. X-rays and/or ultrasound will be taken to ascertain if there is a tumor. The veterinarian will usually take multiple views to check for metastasis. A CT scan or MRI could also be ordered. 

Leiomyoma’s typically have a well-defined, round or oval shape. It’s possible that your vet will suspect a benign tumor based on the shape and lack of metastasis.  Microscopic cell analyzation is usually needed to make a conclusive diagnosis, however.

An endoscopy or colonoscopy may be ordered so that the veterinarian can take biopsies of the tumor. These are invasive procedures which will require a separate appointment, fasting and anesthetic. Exploratory surgery, or laparotomy may also be performed to determine if the tumor is malignant or benign. In many cases, however, the tumor may not be fully analyzed until it is removed, and you may not know until after surgery. 

Leiomyoma are typically treated with surgery. This could be fairly extensive surgery that involves cutting out part of the intestinal wall and sewing it back together. There is a certain amount of risk with any surgery, but tumors that haven’t metastasized are much easier to remove cleanly, without complications. Your dog will spend several days in a veterinary hospital after the surgery. He will be given intravenous fluids and antibiotics to prevent infection, as well as medication for vomiting. 

After returning home there will be a 2 to 3 week recovery period. Your dog will be given pain medication and possibly an antacid. Exercise will be reduced and you will need to check the incision daily to watch for infection. The veterinarian will schedule a check-up two or three weeks after the surgery to ensure the incision is healing properly.

Dogs with leiomyoma usually make a full recovery after surgery. It’s possible your dog will experience post-surgery constipation or ileus, but otherwise you should see an immediate reduction in symptoms. Once the healing period is over, your dog will likely be back to normal.

Since leiomyoma are benign tumors they don’t normally return. Your veterinarian may advise some additional check-ups and X-rays just to make sure there was no metastasis that was missed during the operation, but these are likely to come back clear. Unlike malignant tumors, there’s a good chance your dog will have many years of life left after leiomyoma.