Bone Cysts in Dogs

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

Animal Surgical Center of Michigan

5045 Miller Road

Flint, MI 48507

www.animalsurgicalcenter.com

Phone: 810-671-0088

Key Points

Bone cysts are more common in young dogs

These cysts can cause lameness and pain

Surgery is the best option

Prognosis generally is good with treatment


Anatomy

  • Almost everyone has snapped a chicken bone in two and discoverd that the bone has an other hard shell called the cortex and an inner soft part that contains fat and is called the bone marrow.

 

What is a bone cyst?

  • A bone cyst is an expansile structure within the bone marrow cavity that gradually grows and weakens the bone to the point of causing the bone to fracture
  • A bone cyst can be caused by an arteriovenous fistulae. This is a direct connection of an artery into a vein within the marrow cavity. With time this causes the marrow cavity to expand and thin out the outer part of the bone.

 

Types of bone cysts

  • Simple or unicameral cyst can be caused by trauma, blood clot formation, increased numbers of bone melting cells (osteoclasts), obstruction of blood within veins in the bone (venous obstruction) and fluid accumulation within the bone.
  • Aneurysmal bone cysts can be secondary to a traumatic event to the blood vessels within the bone which leads to the formation of an abnormal connection between an artery and vein (called an arteriovenous fistula). The increased blood supply within the marrow cavity erodes the bone, thus the cyst forms. One dog has been reported to have an aneurysmal bone cyst associated with a chondrosarcoma bone cancer.

 

Signs of a bone cyst

  • Signalment: any breed can be affected, dogs are usually less than 18 months of age (although aneurysmal bone cysts are also found in older dogs), both males and females can be affected
  • Signs: lameness is the most common sign. A swelling of the bone may be noted and this may be painful when direct pressure is applied to the cyst. In some cases the bone may break (fracture), although this is not common.

 

How common is this disease?

  • Uncommon

 

Diagnosis

  • A biopsy is required to make a diagnosis as this lesion can look very similar to bone cancer (see comparison of bone cancer and cyst).
    Bone cyst Bone cancer
    Age: less than 18 months of age Age: mid to older dogs affected
    Slow growing

    Usually rapidly growing

    Typically has a trabeculated bone pattern Typically has bone destruction with trabeculated pattern
    Usually dose not have abundant reaction on outer bone Frequently has abundant reaction on outside of bone(peristalses reaction)
    Usually located near the end of the bone, but can be anywhere Usually located near the end of the bone

    Figure above: Aneurysmal bone cyst in a 1 yr old Labrador that was lame on the forelimb. Figure above: Osteosarcoma (bone cancer) in an 8 yr old Shar Pei that was lame; take note that this tumor does not look much different than the bone cyst seen right other than it is less trabeculated.

 

Treatment

  • Removal of affected bone is usually curative. Radiograph right is of the case as seen above (aneurysmal bone cyst); histological margins were clean in this dog. Dogs can function very well without the lower half of the ulna bone; this dog recovered very well and had no lameness. Take note of the bone screw which was used to reattach the tip of the ulna bone which is attached to the lateral collateral ligament of the carpus (wrist).
  • The inside of the bone cyst can be scraped and filled with bone graft; increased failure rate is seen with aneurysmal bone cysts; aneurysmal bone cysts may transform into a malignant tumor with curettage and grafting.
  • There has been one report of filling the bone cyst with methyl methacrylate (bone cement).

 

Prognosis

  • Favorable prognosis with curettage and bone grafting of simple bone cysts
  • Aneurysmal bone cysts respond better to resection of the affected bone

 

References

  1. MacInnes T J, Thompson M S & Lewis D D. What's your diagnosis? JAVMA 227, 1561-1562 (2005)
  2. Sarierler M, Cullu E, Yurekli Y et al Bone cement treatment for aneurysmal bone cyst in a dog. J Vet Med Sci 66,1137-1142 (2004)
  3. Beckman B W Radicular cyst of the premaxilla in a dog. J Vet Dent 20, 213-217 (2003)
  4. Barnhart M D Malignant transformation of an aneurysmal bone cyst in a dog. Vet Surg 31, 519-524 (2002)
  5. Stickle R, Flo G, Render J Radiographic diagnosis - benign bone cyst. Vet Rad and Ultrasound 40, 365-366 (1999)
  6. Nomura K, Sato K Pelvic aneurysmal bone cyst in a dog. J Vet Med Sci 59, 1027-1030 (1997)
  7. Duval J M, Chambers J N & Newell S M Surgical treatment of an aneurysmal bone cyst in a dog. Vet Comp Ortho Traumatol 8, 213-217 (1995)
  8. Schrader S C, Burk R L, Lin S Bone cysts in two dogs and a review of similar cystic bone lesions in the dog. JAVMA 182, 490-495 (1983)
  9. Kelly C et al The Use of a Surgical Grade Calcium Sulfate as a Bone Graft Substitute: Results of a Multicenter Trial. SECTION I SYMPOSIUM Clinical Orthopaedics & Related Research 382, 42-50, January 2001
  10. Resnick D, Kyriakos M, Guerdon D et al. Tumors and tumor like lesions of bone: imaging and pathology of specific lesions. In: Resnick D, ed. Diagnosis of bone and joint disorders. 3rd ed. Philadelphia: WB Saunders Co. pp 3559–3576 (1995)
  11. Halliwell W H Tumour like lesions of bone. In: Disease mechanisms in Small Animal Surgery Bojrab MJ. Ed Philadelphia: Lea and Febiger. pp 932-943 (1993)
  12. http://www.vetstreamcanis.com/ACI/September08/VMD1/dis02956.asp


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

Board-certification by the American College of Veterinary Surgeons

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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