Nonabdominal surgeries in ferrets (Proceedings)

General Surgical Considerations

In general, ferrets are hardy and make excellent surgical candidates. A complete physical examination and appropriate pre-operative laboratory tests are essential parts of successful surgery. Since ferrets are commonly diagnosed with cardiac disease care should be taken to closely examine the heart and lungs. Some of the clinical signs of cardiac disease such as weight loss, anorexia, inactivity, weakness, and hind limb ataxia are common to other diseases for which surgery may be contemplated. Ferrets often do not cough with cardiac disease and may be asymptomatic. Chest radiographs, an electrocardiogram, and an echocardiogram should be performed prior to surgery if cardiac disease is suspected.

A complete blood count and biochemistry profile should be performed prior to major surgery or in ferrets over two years of age. Any abnormalities should be addressed prior to surgery. The gastrointestinal transit time in ferrets is only three to four hours. They only need to be fasted for approximately three hours prior to anesthesia. A longer fast can induce hypoglycemia even in healthy ferrets and should be avoided. Because of their small size, body temperature should be closely monitored during surgery and recovery. Precautions to prevent heat loss include a circulating warm water blanket, warmed saline for irrigation, administration of warmed intravenous fluids, a radiant heat lamp and a force warm air blanket.

An intravenous or intraosseous catheter should be placed and warmed fluids administered during most procedures at a rate of 10 ml/kg/hr. Also, due to the fact that ferrets can have insulinomas which may or may not be clinically evident, an intravenous fluid solution containing 5% dextrose such as lactated Ringer's solution with added dextrose is often recommended. Ferret skin is relatively thick, so when placing a catheter it is often helpful to make a small nick in the skin with a # 11 scalpel blade or the bevel of a 20 ga needle before attempting to pass the catheter through the skin. A 24 gauge cephalic catheter works well in most ferrets.

A common finding during abdominal surgery is an enlarged spleen. For this reason it is important to avoid damage to the spleen when entering the abdomen as it may cross the ventral midline. Ferrets lack a cecum and the small and large intestines are difficult to distinguish anatomically. The transition from small intestine to colon is grossly marked by only by a change in the pattern of the blood supply.

Post surgical bruising along the incision is not uncommon in ferrets. This is seen even with diligent attention to hemostasis. Gentle tissue handling may help avoid dermal bruising and thumb forceps should be used for counter pressure, not for pinching the skin edges. The discoloration usually resolves within 5 to 7 days, but owners should be warned about the possibility of it developing.

Once the patient is awake encourage it to eat. If it does not eat right away, continue IV fluids with dextrose at a maintenance rate until the patient begins to eat. Even with GI surgery, studies have shown that enterocytes need nutrition to heal mucosal incisions. Withholding food after surgery is not indicated and may delay healing.

As in cats, rebound hyperthermia during recovery from anesthesia occurs in ferrets, so the recovery cage should not be prewarmed and care should be taken to avoid overheating. The body temperature should be closely monitored (q 30-60 min.) until it is about 100° F. Heating devices are removed but body temperature should be closely monitored. There are no reports of clinical problems from this rebound hyperthermia. If the temperature exceeds 104° F consider an IV NSAID or external cooling systems such as cold packs.

Instrumentation

Many of the same instruments used in canine and feline surgery can be used in ferrets. The Stay Retractor is very useful for retracting the abdominal wall for celiotomy or for retracting the wound edges for other procedures (Lonestar Medical Products Inc.; www.LSMP.com). Small needle holders and mosquito forceps are very useful in ferret surgery and microsurgical instruments are ideal. In addition, the small and medium size hemostatic clips (e.g. Hemoclips; Weck Surgical Instruments; RICA Surgical, or Ligaclips; Ethicon) make occlusion of vessels much easier in tight, hard-to-reach places. A generous supply of sterile cotton tipped applicators is very useful for blotting and to aid in tissue dissection.

Anal Sacculectomy

Most ferrets obtained from pet stores are descented so the average practitioner is rarely asked to perform this surgery. Recently there seems to be an increasing number of private breeders making intact ferrets available to the public. Although it has been stated that castration can sufficiently control odor in ferrets, the anal sacs still accumulate very pungent material which they can express during periods of stress, excitement, or aggression. Many times owners prefer ferrets be descented. Anal sac adenocarcinoma, though rare, has been reported in ferrets.

Antibiotics are not necessary if aseptic technique is followed. Animals are placed in the perineal stand position with the tail secured over the back. Clip the area around the anus and place a purse string suture in the anus to prevent fecal contamination of the surgical site. The area is prepared and draped for aseptic surgery. The ducts of the anal sacs open at the 4 and 8 o'clock positions. In the procedure described by Creed (1981) the opening of the duct is clamped to prevent leakage of the pungent anal sac contents during the surgery. A small curved hemostat is placed on the exterior anal sac duct opening. Make a 2 mm diameter circular incision around the duct. Take care to avoid making the incision too deep. Gently retract the hemostat in a dorsal direction and using a #15 or #11 scalpel blade, beginning at the duct opening dissect the anal sphincter muscle off the anal sac. The duct is about 2-3mm long and the sac is 10-20 mm long. The tissue around the duct is glandular in nature containing many perianal glands and appears tough and fibrous. It is often difficult but necessary to establish a plane of dissection between the duct and sac, and the surrounding anal sphincter muscles. As dissection is continued away from the anus, the wall of the anal sac appears smoother and whitish in color. Care should be taken to avoid rupturing the sac, but if this occurs reposition the forceps to grab the edge of the sac where it was opened to control leakage and continue the dissection. The sac lies within the internal and external sphincter muscles and the muscle fibers are carefully scraped off the white tissue of the anal sac. Try to scrape as much muscle off the wall of the sacs as possible. Continue to scrape and bluntly dissect (cotton tipped applicators work well for this dissection) the muscle fibers while putting outward traction on the duct. Sometimes, a small blood vessel is attached to the distal portion of the sac. It should be cauterized or ligated and transected. After the sac has been removed, flush the cavity with sterile saline. There is usually minimal bleeding. The defect does not need to be closed, but if the defect is large, the tissue may be apposed with loose sutures of an absorbable material to provide some tissue apposition. If contamination of the surgical site occurs irrigate the area with sterile saline and administer a broad-spectrum antibiotic for 5-7 days. If there is significant contamination, it is best to leave the defect to heal by second intention.

Complications are rare, but include excessive hemorrhage, postoperative infection or abscess formation, and fecal incontinence. If the patient is incontinent postoperatively, owners should be advised that in most cases sphincter control returns as healing occurs and tissue swelling subsides. Gentle tissue handling and careful dissection minimizing damage to the anal sphincter muscles and innervation will keep complications to a minimum.

Mammary Gland and Preputial Masses

Mammary gland neoplasia is rare in ferrets. Benign mammary adenomas have been reported to occur more frequently in male ferrets, and sometimes in conjunction with preputial masses. Mastectomy or lumpectomy of the mammary masses is usually curative. Preoperative fine needle aspirate with cytologic evaluation is recommended. If it appears to be malignant, more aggressive surgery is indicated.

Preputial orifice masses are also uncommon and may be preputial adenomas or adenocarcinomas. Masses can cause partial urinary obstruction or may be noticed incidentally. Because these masses can be either benign or malignant, a preoperative biopsy is helpful in determining prognosis and how aggressive the surgical resection should be. If malignant, staging including inguinal lymph node aspirates and abdominal ultrasound are indicated.

Smaller, benign masses can be removed followed by reconstruction of the preputial orifice. After removing the mass, 4-0 or 5-0 absorbable suture material is placed in a simple interrupted pattern to appose the subcutaneous and submucosal tissues circumferentially around the new preputial orifice. A second layer of simple interrupted, 4-0 or 5-0 nylon is place for mucosa to skin apposition. In many cases the end of the penis will no longer be covered (basically, a circumcision has been done) but no long term treatment is needed. The penile epithelium will adapt.

With larger, malignant masses, reconstruction can be challenging. In some cases, penile amputation and urethrostomy may be indicated to obtain wide surgical excision. Rotational flaps can be elevated from the flank on both sides if needed.

Prognosis is excellent for adenomas of the prepuce or mammary gland. The outcome for adenocarcinoma of the prepuce or mammary glands is guarded.

Chordoma

Chordomas are tumors formed from embryonic remnants of notochord tissue. They are most frequently found at the distal tail, but may also be located in the cervical or thoracic spine. Chordomas can be locally invasive and may metastasize. On the tail, they are firm, round, lobulated and often ulcerated. Tail amputation can be curative for chordoma of the coccygeal vertebrae if enough healthy tissue (several vertebral segments) is removed proximal to the tumor and metastasis is not present.

Ferrets with cervical and thoracic chordomas present with signs of tetraparesis or paraphrases, respectively, and ataxia referable to the location of the lesion. Myelography, CT or MRI must be done to pinpoint the location of spinal cord compression and determine the optimal surgical approach for attempted removal of the chordoma. Chordomas are slow growing and debulking or removal of a spinal tumor, while not necessarily curative, may relieve neurologic signs and pain for a period of time.

Histologically, chordomas and chondrosarcoma may appear identical. Immunohistochemical staining should be done to differentiate the tumor types. Prognosis for chordoma of the cervical or thoracolumbar vertebrae is guarded due to the potential for recurrence or metastasis as complete resection is generally not possible. Prognosis after tail amputation for chordoma is very good if surgical margins are free of tumor.

Perineal Urethrostomy

Repeated urinary obstruction due to crystaluria in male ferrets can be treated palliatively with perineal urethrostomy. Crystaluria has been associated with the presence of plant material in the diet. Feeding commercially available ferret foods have resulted in a decrease in incidence of lower urinary tract disease in ferrets so this procedure is not as commonly done as it was in years past. It is also indicated, as mentioned previous, for management of preputial neoplasia where penile amputation is indicated. However, this procedure is NOT effective for urinary obstruction secondary to paraprostatic cysts associated with adrenal disease. In these patients the obstruction is secondary to compression from the cyst and is cranial to a urethrostomy site. A cystotomy should be performed when cystic calculi are present.

Place the anesthetized ferret in a perineal stand and place a purse string suture in the anus. It is best to pass a urinary catheter to relieve the obstruction and to make it easier to identify the perineal urethra. It can be quite difficult to get a 3.5 Fr (tom cat size) catheter in a male ferret. A 3.0 Fr is much easier to pass and is recommended. The urethrostomy site is located between the caudal aspect of the os penis and the pelvic urethra, about 1-2 cm ventral to the anus. Make a skin incision and expose the urethra. Make a 1-1.5 cm incision in the penile urethra (facilitated by an indwelling 3.0 urethral catheter). Avoid incising the corpus cavernosus on both side of the urethra which will result in marked hemorrhage. If an indwelling urinary catheter is not already present, one can be placed through the incised urethra at this time to drain the urinary bladder. The urethra is narrowest through the os penis and it is wide enough in the perineum to accept a 3.5 Fr catheter. Oppose the urethral mucosa to skin edges using 5-0 or 6-0 monofilament, nonabsorbable, simple interrupted sutures. It is best to place the proximal apical sutures first to insure accurate placement in this critical location. Make the final opening at least 1cm long. Postoperative care includes antibiotics, IV fluids, analgesics and a collar, if possible, to prevent self-mutilation. Healing is usually uneventful with no long-term complications. Because of the fine sutures and delicate tissues it is best to perform suture removal under heavy sedation or brief anesthesia.

Oronasal Fistulae

I have seen oronasal fistulae in ferrets who have chewed on electrical cords with resultant necrosis of the palate as well as after surgery for oral cancer, mainly squamous cell carcinoma. These fistulae are significantly more difficult to get closed than the same type of lesion in dogs and cats.

The standard recommendation for closing an oronasal fistula in a dog or cat is to achieve a single layer closure. Because the oral cavity is very vascular, it tends to heal well and quickly. The single mucosal layer can be elevated from the mucosa of the hard palate or from the buccal mucosa. When I have tried this technique in ferrets, the closure has failed. There are techniques described for closing difficult oral defects (fistulae, cleft palate, cancer excision, and dental abscesses) that do not close with standard techniques and for ferrets, a two mucosal layer closure is seems to work best.

Using a single mucosal flap technique, the oral mucosa is closed but the nasal mucosal surface is left to heal by second intention. By creating two mucosal surfaces (one nasal and one oral), each having its own blood supply, with a tension-free closure, the chances from primary healing are greatly improved. Two layers of mucosa are elevated and positioned so that one mucosal surface is on the nasal cavity side and the other is on the oral cavity side. This results in the raw surfaces (submucosal surfaces) being in contact and the mucosal side lining the oral and the nasal cavity, separately.

The first ferret I treated with this problem had an oral squamous cell carcinoma and a maxillectomy was performed using standard technique. At suture removal, a large oronasal fistula was present. A second single mucosal surgery was performed and failed as well. At the third surgery, with healthy mucosa being difficult to find, a double mucosal closure was performed and, that time, it healed uneventfully. So, even after multiple surgeries the prognosis for healing with a double mucosal closure appears to be good.

Salivary Mucoceles

The clinical presentation is the same as in dogs with a non-inflamed cystic lesion around the head and neck. Aspirate cytology shows a mucous/proteinaceous background with few cells. Grossly the material is very thick and tenacious.

The anatomy of the salivary glands of ferrets is not the same as that of dogs. In dogs, over 90% of salivary mucoceles are treated surgically by removal of the mandibular and monostomatic (caudal) sublingual salivary glands. Ferrets do not have a polystomatic sublingual salivary gland and the monostomatic gland is not intimately associated with the mandibular gland as it is in dogs. The sublingual gland is located deep to (medial to) the digastricus muscle under the mandibular lymph node. The digastricus muscle must be incised to access this gland. Ferrets have a buccal salivary gland that is larger than the sublingual and appears to be the most common source of a mucocele in ferrets.

My surgical approach to dealing with salivary mucoceles in ferrets is to dissect the cyst out very carefully tracing it to its source. Once the salivary gland from which the cyst has formed has been identified, it is removed.