Fatty Tumors - Lipomas

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Article Written by Dr. Daniel A. Degner, Board-certified Veterinary Surgeon (DACVS)

Key Points

Fatty tumors commonly are only a cosmetic issue

Fatty tumors involving the thigh, armpit (axilla), in the throat and other vital areas can be functionally problematic and mandate surgical removal

Infiltrative lipomas do not spread, yet recurrence is a problem

Liposarcomas are locally invasive and have a relatively low spread rate


Introduction

Lipomas are benign tumors that are composed of fat. They can be located in many different locations on the body. Commonly, these tumors are soft and located between the skin and muscle layers. These tumors are freely moveable. Sometimes they are located between the muscles and seem to have a more firm consistency and are not moveable. Lipomas can be located anywhere within the body. These tumors are slow growing, but frequently will grow to a very large size with time. Most of these tumors are cosmetically displeasing to the pet owner, yet some will impede bodily function. Lipomas growing between the muscles of the limb will eventually impede the function of the limb and cause lameness. If located in the throat area or beneath the tongue, breathing or swallowing difficulties may be noted. Lipomas are frequently multiple on the body and do not spread to other parts of the body. Lipomas are classified as simple (noninfiltrative) or infiltrative. Simple lipomas are easily dissected out of the body. Infiltrative, as the name implies, is a type of fatty tumor that has grows into adjacent muscles and tissues. These tumors have a moderate tendency to recur, but these tumors do not metastasize. Liposarcomas are malignant fatty tumors that may metastasize to other parts of the body.

 

Signs

Lipomas are seen in mid to older dogs. Cats rarely develop lipomas. Lipomas are tumors that frequently are not attached to underlying tissues (freely moveable), however, may seem so if they are located between muscle layers. Other more serious tumors may mimic the appearance and feel of a benign lipoma. One example is a mast cell tumor located in the fatty tissue (subcutaneous tissues) beneath the skin. For this reason, even tumors suspected to be a lipoma should always be biopsied. If the tumor is growing rapidly, and it previously was diagnosed as a lipoma based on fine needle biopsy, another biopsy should be done. We have also seen some combination tumors such as lipoma combined with mast cell tumor and lipoma combined with a sarcoma - in such cases a diagnosis of only a lipoma was made prior to surgery, yet the patient had another concurrent tumor in the same mass. For this reason it is advisable to submit all removed lipomas for histopathology (biopsy analysis).

Below are examples of lipomas in canine patients:

Lipoma under the tongue

Lipoma involving anus and vulva

 

Lipoma in abdomen (falciform lipoma)

 

Lipoma on front of chest

 

Lipoma between the thigh muscles; note the very thickened thigh

 

Sciatic nerve preserved following removal of lipoma from thigh

 

Simple lipoma removed from thigh above

 

Infiltrative lipoma - note fat within muscle fibers

 

Diagnosis

The diagnosis of a lipoma is made by a fine needle biopsy. This involves inserting a needle into the mass, aspirating a small sample from the mass, spaying the sample on a glass slide, staining the sample with cytology stains, and examining the sample under a microscope. Fat cells or fatty droplets are seen under the microscope. Ultrasound, CT scan or x-ray may be needed to determine the extent of the tumor when it is located in regions that are difficult to operate. Diagnosis of an infiltrative lipoma is largely is based on finding fatty infiltration of muscles and fascia at the time of surgery and the biopsy will also confirm the gross surgical findings. Liposarcomas may require collecting a larger biopsy sample (core biopsy or wedge biopsy) to achieve a preoperative diagnosis. In preparation for surgery, preoperative blood work including a complete blood count, chemistry profile, and urine testing are recommended to ensure that your pet is healthy and can safely undergo anesthesia and surgery.

 

Preparation for surgery

The pet should be fasted prior to surgery, as instructed by the surgical team. Water is usually permitted up to the time of admission to the hospital. An antacid such as Pepcid AC may be prescribed and should be administered by 6 AM on the day of surgery; this treatment will help reduce the risk of esophagitis (heartburn) in the postop period. The surgical team should be informed of any medications that your pet is currently receiving. The pet should not receive any aspirin within 1 week of surgery, as this medication will thin the blood and increase the risk of bleeding. Just prior to surgery, your pet will receive a sedative, have an intravenous catheter placed for the administration of intravenous fluids and intravenous medications, be induced under general anesthesia with medication(s), and have a breathing tube (endotracheal tube) placed to allow delivery of oxygen and gaseous anesthesia. The surgical site will be clipped and cleansed with an anti-septic solution in preparation for surgery. While under general anesthesia, the pet's breathing will be assisted with a ventilator and vital parameters such as heart rate, respiratory rate, core body temperature, blood pressure, oxygenation of the blood (pulse oximetry), exhaled carbon dioxide (capnography), and heart rhythm (EKG) will be monitored to ensure the pet's well being. Pain will be controlled both during and after surgery with analgesics (pain-controlling medication). Please note that each surgical and anesthesia team may elect to chose a different, but effective analgesia protocol.

 

Surgery

An incision is made over the lipoma that is to be removed. Simple lipomas can be removed with relatively small incisions. If there is a very large void (dead space) where the tumor was previously removed, a drain may be inserted to help prevent formation of a fluid pocket in the surgical site. This is done on a case by case basis.

Infiltrative lipomas require a much more aggressive surgery with removal of any muscle or fascial tissues that are invaded with the tumor.

Liposarcomas require an aggressive resection with removal of the mass en bloc and a good margin of normal tissue.

 

Aftercare

Following surgery, the patient will receive pain-relieving medication to ensure a comfortable recovery. A combination of nonsteroidal anti-inflammatory, local anesthetics and narcotics are used to control pain. Intravenous fluid therapy is administered to ensure that your companion will remain well hydrated during and after surgery. Most patients can go home on the day of surgery. If an invasive and more painful surgery was performed, the pet may need to be hospitalized overnight to control pain. At home, the incision should be checked for signs of infection. Your pet should not lick the incision, as this could open the incision or cause infection. If necessary, an Elizabethan collar can be placed on your companion to prevent licking and chewing at the surgical site. Exercise should be restricted for about 3 to 4 weeks after surgery.

 

Results

Recurrence of simple lipomas after surgery is uncommon. Thomson reported 11 cases of thigh lipomas, in which 10 of them had surgery. All of these cases had simple lipomas and no tumor recurrence was seen over a median follow-up period of 17 months. In my experience, about 5 to 10% of the lipomas within the thigh are infiltrative. Although many of these thigh lipomas are intimately associated with the sciatic nerve (can be wrapped around the nerve), I have never seen dysfunction of the limb due to sciatic nerve damage following lipoma removal.

Infiltrative lipomas recur in about 30 to 50% of the cases and it may take up to one year until the tumor needs to be debulked again. Bergman reported a recurrence rate of 36% with a median time to recurrence of 239 days; the median disease free interval 1 year post surgery was 67%. McEntee reported irradiation of infiltrative lipomas in 13 dogs. Ten of the 13 dogs had surgery to remove the tumor prior to radiation therapy. One of 13 cases had tumor recurrence. It is difficult to determine the benefit of radiation therapy, but there may be some benefit.

In a report of 56 patients, liposarcomas were found to be locally invasive, but uncommonly metastasized (4/56 patients). Median survival times were 1188, 649 and 183 days, respectively, for patients hat had wide excision, marginal excision and only an incisional biopsy. Factors that did not influence patient survival included tumor size, clean vs. dirty surgical margins, tumor location, and the histological subtype.

 

References

  1. Thomson MJ, Withrow SJ, Dernell WS, Powers BE. Intermuscular lipomas of the thigh region in dogs: 11 cases. J Am Anim Hosp Assoc 1999; 35(2)165-7.
  2. Bergman PJ, Withrow SJ, Straw RC, Powers Be. Infiltrative lipoma in dogs: 16 cases (1981-1992). J Am Vet Med Assoc. 1994;205(2):322-4.
  3. McEntee Mc, Page RL, Mauldin GN, Thrall DE. Results of irradiation of infiltrative lipoma in 13 dogs. Vet Radiol Ultrasound. 2000; 41(6):554-6.
  4. Baez JL, Hendrick MJ, Shofer RS, et al. Liposarcomas in dogs: 56 cases (1989-2000). J Am Vet Med Assoc 2004; 224:887-91.

Frequently Asked Questions After Surgery

When should my dog have the first bowel movement after surgery?

  • Many dogs will not have a bowel movement for the first 4 to 5 days after surgery
  • Reasons that a dog will not have regular bowel movements after surgery include:
    • The dog has been fasted prior to surgery
    • Dogs do not eat well during the hospital stay
    • They frequently do not eat well when they go home
    • They are fed highly digestible food that produces little stool
    • Pain medication that contain narcotics (such as morphine, fentanyl patches, and tramadol) can be constipating
  • If a pet does not have a bowel movement on the 5th day of being home, a stool softener such as metamucil can be fed
    • Dose of metamucil is 1 tsp per 25 Kg mixed in with each meal (canned dog food); feed immediately after mixing, as the metamucil will gel the food and may make it less palatable

My pet had surgery and will not eat.  What can be done?

  • Dogs
    • Most pets will not eat their regular dog food after surgery, especially if it is kibble.
    • Offer a cooked diet having a 1:1 ratio of a protein source and carbohydrate source.  The protein source can be any meat (example: chicken breast, turkey breast, lean hamburger) that is low in fat and should be cooked (drain off all fat after the meat has been cooked).   The carbohydrate can be pasta, potato or white rice.
    • Try canned dog food; to enhance the flavor sprinkle a very small amount of garlic powder or chicken or beef broth (Chicken-in-a- MugTM or Beef-in-a-MugTM products)
    • Try Gerber strained meats for babies such as the chicken, beef, turkey, or veal
    • Try Hill's A/D diet available at most veterinary hospitals
    • Hand feeding: place a small amount of food in the mouth so that your dog gets the flavor
    • Warm the food slightly in a microwave, as the food will be more aromatic; stir the food before feeding and test the temperature on the bottom side of your wrist; it should only be luke warm.
    • Remember that most pets will not eat the first day or two after they get home from surgery
  • Cats
    • Offer smelly foods that contain fish such as tuna or smelly cat foods
    • Try Gerber strained meats for babies such as the chicken, beef, turkey or veal
    • Hand feeding:  with your finger place a small amount of food on the roof of your cat's mouth; use a syringe to get soft food into the mouth
    • Warm the food slightly in a microwave as the food will be more aromatic; remember to stir the food before feeding and test the temperature; it should be only luke-warm
    • Some cats will only eat dry food, try kibble if your cat normally has been fed that food
    • Petting and stroking your cat frequently will help to stimulate appetite
    • Remember that most pets will not eat the first day or two after they get home from surgery
    • Appetite stimulants such as cyproheptadine may be helpful
    • If your cat refuses to eat anything for 7 days a stomach tube or nasogastric tube should be placed to provide nutrition so that a serious liver problem (hepatic lipidosis) does not develop

My pet is vomiting.  What can be done?

  • The first thing for you to discern is whether your pet is vomiting or regurgitating.  Both will result in fluid or food being brought up.  Vomiting always will have heaving or retching of the abdomen prior to expulsion of the vomitus.  Regurgitation is not associated with heaving and the pet usually just opens the mouth and fluid or food will be expelled.  Usually the regurgited material will be clear or brown colored fluid. 
  • Next is to identify the cause of the vomiting or regurgitation.
  • Causes and treatment of vomiting after surgery
    • When some pets return home after a stay in the hospital they may drink excessive amounts of water at one time and then vomit; if this appears to be the case, the water should be limited to frequent smaller amounts.
    • Medications such as antibiotics, narcotics or nonsteroidal anti-inflammatory medication commonly cause vomiting after surgery.  In order to see which medication is causing the problem, the administration of each drug should be separated 2 hours apart.  Usually the pet will vomit or appear nauseated (drooling and sick look) within 1 hour of administration of the medication that they are sensitive to.  The antibiotic in some cases may be changed to a different one, or may be discontinued. 
    • Stomach upset from anesthesia is a potential cause of vomiting and will pass within a couple of days. 
    • An uncommon cause of vomiting after surgery is internal organ failure.  Blood testing will confirm this problem. For this reason vomiting should not be ignored if it persists for more than 24 hours.
    • If your pet had surgery of the bowels or stomach, vomiting is always a concern, as it may indicate that infection of the abdominal cavity, called peritonitis, is present.  Do not ignore this sign.
    • Symptomatic treatment of vomiting involves withholding food for 12 to 24 hours, then introducing small amounts of bland food such as rice and lean cooked hamburger, if your pet does not vomit after that then gradually wean him/her back onto the regular diet after 3 days.  In order to decrease the acidity of the stomach, Pepcid AC 0.5 mg/kg can be given by mouth twice daily for 5 days.  Metoclopramide and Cerenia are good anti-vomiting medications for dogs and cats.  You should always consult a veterinary healthcare professional before administering medication.
  • Causes and treatment of regurgitation after surgery
    • The most common cause of regurgitation is reflux of acid from the stomach into the esophagus while your pet is under anesthesia.  Acidic fluid from the stomach can cause a chemical burn of the esophagus and result in a bad case of heart burn, called esophagitis.  This results in poor motility of the esophagus, therefore water and food will accumulate in this structure.  In most cases, esphagitis is self-eliminating and will resolve within two or three days. 
    • If the esophagitis is severe the esophagus may develop one or more strictures.  A stricture is a narrowing or stenosis of the esophagus and does not allow passage of food down the esophagus, in regurgitation that lasts longer than one week.  This problem should be brought to the attention of your pet's doctor within the first two weeks so that it can be treated by ballooning the stricture (minimally invasive procedure, as it is done with the aide of an endoscope).  If an esophageal stricture is chronic surgery is needed.
    • Symptomatic treatment of regurgitation caused by esophagitis includes feeding bland food, and administering a coating agent (sucralfate) and an acid blocker (omeprazole or other).  Consult a veterinary health care professional if the regurgitation continues for more than a couple of days.

How do I know that my dog is in pain following surgery?

  • Signs of pain include
    • crying
    • biting if you get near the surgical site
    • grimacing (lips are pulled back and the the dog looks anxious)
    • tragic facial expression
    • panting
    • restlessness and unable to sleep; pacing
    • if abdominal surgery was done the pet will not lie down on the incision, or will continually sit up in spite of appearing very tired
    • the worst pain will be for the first 2 to 3 days after surgery

What can I do to control my dog's pain?

  • Narcotic medications that control pain: tramadol, butorphanol, Duragesic (fentanyl patch)
  • Anti-inflammatories used to control pain: Deramaxx, Rimadyl, Previcox, or Etogesic
  • If an orthopedic surgery has been done cold packing the surgical site may be helpful
    • A cold pack may be a pack of frozen peas, crushed ice in a Ziploc bag, or a cold gel pack; place a thin barrier between the skin and the cold pack.  An alternative to a cold pack is to freeze water in a styrofoam cup; after frozen cut the bottom of the styrofoam cup out. Cool the surgical site around the incision by rubbing the exposed ice directly on the skin in a circular pattern.  Cooling the surgical site helps to numb the area.

How do I know that my cat is in pain following surgery?

  • Pain is more difficult to assess in cats versus dogs, as signs can be more subtle and they usually do not vocalize when in pain
  • Signs of pain in a cat include the following:
    • biting if you get near the surgical site
    • growling or deep cry
    • not wanting to eat
    • hiding and not wanting to be near owner (remember that this could also be caused by the cat just being upset about leaving home and coming back)

What can be done for pain at home for my cat?

  • Pain medication such as buprenorphine or a Duragesic (fentanyl) patch
  • Tylenol will kill a cat as they lack abundant glutathione enzyme in the liver
  • Anti-inflammatories can be used, but the dose is much less than dogs

Is it okay for my pet to lick the incision?

  • If a dog licks the incision, the healing process may be delayed.
  • Licking can remove stitches and cause the incision to open
  • Licking can become a severe habit that is difficult to break
  • Licking can cause infection as the mouth has many bacteria
  • Dogs will frequently lick the incision when the owner is not watching such as at night time; if the skin looks red or excoriated the most common cause is from licking.
  • To stop your pet from licking the following can be tried:
    • Elizabethan collar can be placed on the neck; this will not help stop your pet from scratching at the region
    • Cervical collar (bite not collar) is a less awkward device and can be effective at stopping a pet from licking the surgical site
    • A tee shirt can be used to cover an incision on the chest or front part of the abdomen; gather the waist of the shirt up over the dog's back and wrap an elastic band around this part of the shirt.
    • A bandage or sock can be used to cover an incision on a limb; fasten the top of the sock to the dog's limb with tape.
    • Bitter apple can be applied around the incision; many dogs will continue to lick  after application of this topical
    • Bitter Apple and Liquid HeetTM (obtain this from a drugstore...it is used for sore muscles) mixed in a 2:1 ratio can be applied around the skin incision
    • Antipsychotic medication in some cases is needed

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What does it mean?

  • Four years of advanced training in surgery beyond the Doctor of Veterinary Medicine Degree

  • Experience in the development of new surgical treatments

  • Rigorous examination by the American College of Veterinary Surgeons to ensure competency in advanced surgical techniques

  • Assurance that a veterinarian is a surgical specialist

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