Ferret- Abdomainal Surgical Procedures. Part Ii

Vol. 21, No. 11 November 1999

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FOCAL POINT ★ Ferret abdominal surgical procedures are similar to those in other small animals and can be readily performed in most general practices.

KEY FACTS ■ To prevent stricture following enterotomy, the longitudinal incision on the antimesenteric boarder should be closed transversely, thereby widening the bowel lumen. ■ Splenomegaly in ferrets is frequently a benign condition, and routine splenectomy is not recommended. ■ Liver biopsy is indicated during most exploratory celiotomies. ■ To prevent recurrence of urolithiasis after a cystotomy, ferrets should be placed on a diet that contains no plant material. ■ Complete blood and platelet counts should be performed on all intact female ferrets before performing an ovariohysterectomy.

Ferret Abdominal Surgical Procedures. Part II. Gastrointestinal

Foreign Bodies, Splenomegaly, Liver Biopsy, Cystotomy, and Ovariohysterectomy* University of Florida

Jason Wheeler, DVM R. Avery Bennett, DVM, MS ABSTRACT: Ingestion of foreign bodies is prevalent in young ferrets; as they age, obstruction with trichobezoars becomes more common. Splenomegaly, a common but typically benign condition in ferrets older than 2 years of age, is usually caused by extramedullary hematopoiesis. Liver biopsy can be a valuable diagnostic tool and is indicated during most exploratory celiotomies. Urolithiasis occurs in male and female ferrets. Being induced ovulators, female ferrets can develop hyperestrogenemia when in estrus for prolonged periods; spayed ferrets may occasionally have hyperestrogenemia as a result of residual ovarian tissue. Pyometra is rare in this species.

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erret abdominal surgery is similar in many ways to abdominal procedures routinely performed in dogs and cats. Knowledge of the conditions most frequently requiring surgery, variations in anatomy, and pathophysiology of the condition being treated will enable general practitioners to perform routine abdominal surgical procedures in ferret patients. Part I of this two-part series discussed surgical procedures involved in the excision of adrenal gland neoplasia and treatment of paraurethral and prostatic cysts and pancreatic beta-cell tumors (insulinomas). Part II addresses surgical techniques related to the removal of gastrointestinal (GI) foreign bodies, splenomegaly, liver biopsy, cystotomy, and ovariohysterectomy.

GASTROINTESTINAL FOREIGN BODIES Foreign-body ingestion is particularly a problem in ferrets younger than 1 year of age. Young ferrets enjoy chewing on and ingesting soft rubber (e.g., latex or foam rubber), cork, soft plastics, pencil erasers, and occasionally cloth. After they *Part I of this two-part presentation appeared in the September 1999 (Vol 21, No. 9) issue of Compendium.

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reach 1 year of age, their chewing surgery, but surgery should not be behavior decreases greatly. In older postponed until the next day. A ferrets, GI obstruction or partial complete abdominal exploratory obstruction with trichobezoars besurgery is performed, and the encomes a relatively frequent probtire GI tract is evaluated for the lem.1–4 Clinical signs in ferrets with presence of multiple foreign boda GI foreign body that is not causies. The techniques for gastrotomy ing an acute obstruction are vague and enterotomy in ferrets are anand include intermittent anorexia; alogous to those used in other dark, tarry stools; hindlimb weakspecies.5,6 The gastrotomy incision is ness; and depression. Gradual made in a relatively avascular reweight loss and potentially severe gion of the stomach between the wasting may occur after several lesser and greater curvature after weeks of illness. Vomiting, which the stomach has been isolated occurs in some animals with GI for- Figure 1A with saline-moistened sponges. eign bodies, is an infrequent finding Stay sutures may be used to allow in ferrets.4 Clinical signs are more dramatic the surgeon to control the inciwhen a GI foreign body completely sion. A two-layer closure using 4obstructs the pylorus or migrates 0 monofilament absorbable mainto and obstructs the small intesterial is recommended; the first tine, as would be expected in any layer should be a simple continupatient with acute GI obstruction. ous appositional pattern and the Signs include severe depression and second layer an inverting pattern dehydration, vomiting, hindlimb (e.g., Cushing or Lembert). weakness, and crying in pain. Even The diameter of the small inteswith complete obstruction, vomittine of ferrets is quite narrow along ing is an inconsistent clinical sign. the entire length, and there are reDiagnosis of a GI foreign body is ports of intestinal stricture followFigure 1B based on signalment, history, physiing routine enterotomy.1,7 Addical examination, and radiography. Figure 1—When performing an enterotomy in a tionally, it is recommended that Most ferrets have a relaxed abdo- ferret, it is best to make a longitudinal incision the enterotomy be made on the in the antimesenteric border of the intestine (A). men that is easy to palpate; thus Points A and B depict the orad and aborad ex- antimesenteric border of the intesclinicians are usually able to palpate tents of the incision, respectively. To minimize tine in the aborad (smaller) porthe foreign material within the the risk of stricture formation, the enterotomy is tion—this is usually the healthier stomach or the intestine of most closed transversely so that the first suture is portion of bowel.8 The enterotopatients. Small trichobezoars may placed to bring the orad extent of the incision my is made longitudinally along be difficult to palpate, however, be- (A) in apposition with the aborad extent of the the antimesenteric border. To mincause they compress easily and thus incision (B). The remainder of the enterotomy imize postoperative stricture formay go undetected. A foreign ob- is then closed (B). This increases the lumenal di- mation, the enterotomy is closed transversely, which potentially wiject or a gas-and-fluid pattern with ameter in the area of the enterotomy. dens rather than narrows the lumen dilated loops of intestine consistent at the enterotomy site (Figure 1). with ileus secondary to intestinal obstruction may be seen After the gastrotomy or enterotomy is closed, conon radiographs. Occasionally, the foreign body will be taminated instruments are exchanged for sterile ones, opaque and visible on radiographs. A gas-distended stomsurgeons’ gloves are changed, and the abdomen is irriach is consistent with gastric outflow obstruction and is gated before closure. Patients are maintained on intraan indication for surgery as soon as possible. Contrast ravenous fluids and analgesics until food and water are diography may occasionally be beneficial but is not necesoffered the day after surgery. Antibiotics are adminissary in the majority of ferrets with GI obstruction.2 Treatment of GI foreign bodies involves exploratory latered if indicated based on the level of abdominal conparotomy and gastrotomy or enterotomy to remove the tamination. The prognosis following surgery is generalforeign body. This is considered an emergency procedure. ly good, although clients must take steps to prevent The patient should be stabilized and rehydrated before recurrence. TRICHOBEZOARS ■ RADIOGRAPHY ■ LAPAROTOMY ■ GASTROTOMY ■ ENTEROTOMY

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SPLENOMEGALY In ferrets, the spleen is easily palpated and readily visualized on abdominal radiographs. Splenomegaly is relatively common in ferrets 2 years of age or older and may result from a variety of conditions,2 including lymphoma, pancreatic beta-cell tumor, cardiomyopathy, adrenal neoplasia, systemic mast cell tumors, Aleutian disease, eosinophilic gastritis, hemangiosarcoma, primary splenic neoplasia, hypersplenism, splenitis, and extramedullary hematopoiesis.9 Splenomegaly is generally a benign condition in ferrets, and routine removal of the spleen is not recommended. However, a spleen that rapidly increases in size over a very short period or that is irregular in shape, painful, or so large that it interferes with abdominal visceral function is cause for concern, and splenectomy or partial splenectomy may be indicated. Splenic extramedullary hematopoiesis is one of the most common histologic diagnoses in ferrets with splenomegaly.10 Preoperative biopsy or fine-needle aspiration cytology of the spleen is recommended because partial splenectomy is preferred over complete removal if possible. Removal of the spleen is generally contraindicated in ferrets with bone marrow hypoplasia because the spleen is the primary site of hematopoiesis in these patients11; partial splenectomy can preserve this potentially vital function. Lymphoma, myelogenous leukemia, and nonvascular neoplasia (e.g., leiomyosarcoma, fibrosarcoma) may also be diagnosed via splenic biopsy. Percutaneous biopsy is contraindicated in cases of hemangiosarcoma as it may induce fatal hemorrhage; however, this tumor type is uncommon in ferrets. Ultrasound can help determine the safety and efficacy of percutaneous biopsy and is very useful for guiding the needle to collect an appropriate sample. Fine-needle aspiration is recommended because it is simple, carries little risk, and provides excellent samples. The spleen is isolated and held in position. Using a 25-gauge, 1-inch needle on a 6-ml syringe, negative pressure is applied as the needle penetrates the spleen and is maintained while the needle is advanced into the parenchyma. Negative pressure is then discontinued and the needle slowly withdrawn. Releasing pressure before withdrawal minimizes the risk of blood contamination. Splenic biopsy may be performed during an exploratory celiotomy. If the sample is to be taken from the margin, mattress sutures are placed through both surfaces of the spleen. The parenchyma is transected distal to the sutures, which are left in place to control hemorrhage. To remove a central portion, two parallel incisions that are long and deep enough to obtain a representative sample are created; two additional inci-

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sions are then made perpendicular to the original incisions, creating a square or rectangular section of spleen to be removed. Mattress sutures are placed across the defect to control hemorrhage. Partial splenectomy, which allows retention of normal splenic functions, is indicated to treat such nonneoplastic conditions as extramedullary hematopoiesis. This procedure should be performed only when the spleen is so large that it interferes with normal physiologic functions. The vessels supplying the portion of the spleen to be removed are double ligated or clipped and transected at the hilus (Figure 2). In most cases, the caudal portion (i.e., the free end) of the spleen is removed, which is less likely to result in vascular compromise of the stomach. After several (5 to 10) minutes, a line of demarcation will be visible between the viable portion of the spleen and the section that has been deprived of its blood supply. Using this line of demarcation, the splenic tissue is pinched between the thumb and forefinger and the pulp is milked toward the ischemic portion. Atraumatic (e.g., Doyen) forceps are placed along the flattened area, and the spleen is transected a few millimeters distal to the clamp. The cut surface along the clamp is then sutured with an absorbable material in a continuous pattern to control hemorrhage. Digital pressure or a hemostatic agent can be used to control residual hemorrhage after the clamp is removed. Alternatively, mattress sutures are placed through the parietal and visceral surfaces of the spleen along the line of demarcation and the spleen is transected distal to the sutures. Automatic stapling devices, if available, are excellent for performing partial splenectomy. Total splenectomy is performed beginning at the caudal or free end of the spleen by double ligating or clipping the splenic and short gastric vessels at the hilus of the spleen and transecting the vessels between the ligatures. An alternative, faster method involves ligation of the short gastric artery and vein and the splenic artery and vein distal to the pancreatic branch. Care is taken to avoid damaging the pancreatic branch, which can result in ischemic pancreatitis. Following splenectomy, dogs are less tolerant of experimentally induced hemorrhagic shock and do not respond as well to strenuous exercise.11 Sepsis following splenectomy, as occurs in humans, has not been reported as a complication in animals.12 The major concern with total splenectomy in ferrets with splenic extramedullary hematopoiesis is that chronic anemia may occur in the absence of splenic production of erythrocytes.11

LIVER BIOPSY The liver of ferrets has six lobes: left lateral, left medi-

EXTRAMEDULLARY HEMATOPOIESIS ■ FINE-NEEDLE ASPIRATION ■ PARTIAL SPLENECTOMY

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Figure 2C

Figure 2A

Figure 2B

Figure 2—When performing a partial splenectomy, care should be taken to avoid ligating the short gastric vessels between the

stomach (St) and spleen (Sp; A). It is easiest to remove the caudal (i.e., free) portion of the spleen. The hilar vessels are ligated and divided (B), which results in infarction of the portion of the spleen supplied by these vessels. Finger compression allows a clamp to be placed along the line of demarcation. The capsule is incised a few millimeters distal to the clamp. The capsule is then closed with a simple continuous pattern to control hemorrhage before the clamp is removed (C).

al, quadrate, right medial, right lateral, and caudate.13 Liver biopsy is indicated during most exploratory celiotomies. Conditions such as hepatic lipidosis, lymphoma, metastatic pancreatic beta-cell tumor, and other hepatic diseases may be diagnosed using hepatic biopsy.7 The conformation of the liver lobes varies among individual ferrets. In some patients, a pointed portion of a liver lobe may be identified and thus a suture fracture technique is appropriate. A ligature of 4-0 braided absorbable suture is looped around the protruding section of liver and tightened to cut through the liver parenchyma while ligating any vessels. Scissors are used to transect the tissue distal to the ligature, and the ligature is left in place to control hemorrhage. If all lobes have a rounded configuration, a transfixation suture fracture technique is used. This method is also used if biopsy of a specific section of liver is desired because of the presence of a lesion. An atraumatic needle is passed through the liver parenchyma, and the suture is tied to cut through the liver on one side. The second throw on the suture is made to cut through the liver on the other side, ligating the vessels supplying the liver distal to the ligature (Figure 3). The tissue is then transected distal to the ligature, allowing excision of the biopsy specimen. Any residual hemorrhage can be controlled with a hemostatic agent.

CYSTOTOMY Urolithiasis occurs in male and female ferrets of any age. The calculi are generally composed of magnesium ammonium phosphate (struvite) and are frequently secondary to bacterial infection caused by such agents as Staphylococcus and Proteus.14,15 Clinical signs associated with urolithiasis include dysuria, hematuria, and painful urination. Diagnosis is based on clinical signs, palpation of calculi and/or a large bladder, and radiographic or ultrasonographic evidence of calculi or crystals within the bladder. In some cases, crystals are visible in voided urine. It is frequently difficult to catheterize a ferret (male or female) that has a urinary tract obstruction. A tomcat catheter (3.5 Fr) can be placed in many male ferrets with urinary obstruction; however, it can be quite challenging. A 3.5-Fr red rubber catheter is often easier to place because it is more flexible and bends around the ischium more easily. As an alternative, an 18-gauge polytef catheter may be used. The catheter must be long enough to reach the bladder. Infusing 0.2 to 0.3 ml of 1% or 2% lidocaine into the urethra and administering 1 to 2 mg/kg diazepam intramuscularly as a smoothmuscle relaxant may help dilate the urethra to allow passage of the catheter. A ferret urethral catheter (Cook Veterinary Products, Bloomington, IN) is 3 Fr, fits into the urethra better, and is very useful in the management of ferrets with urethral obstruction.

LIVER CONFORMATION ■ SUTURE FRACTURE TECHNIQUE ■ UROLITHIASIS

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Lesion

Figure 3A

Figure 3B

Figure 3C Figure 3—When a biopsy of the liver is

needed from an area without a projection (A), a transfixation suture fracture technique is used. The suture is passed through the liver parenchyma (B) and tied to one side of the lesion to cut through the liver parenchyma and ligate the vessels within the tissues (C). The same suture is then tied on the opposite side of the liver to cut through parenchyma and ligate vessels on that side (D). The biopsy sample is then transected distal to the ligature (E). Figure 3D

Figure 3E

If a ferret can be catheterized, the condition may be managed medically similar to the management of cats with urolithiasis. Cystotomy is indicated for removal of large calculi and irrigation of the urethra. Standard approach and technique for cystotomy are used in ferrets. A ventral cystotomy is performed, and calculi are removed. The apex of the bladder should be inspected for the presence of a diverticulum, which has been reported in ferrets.7 Culture of the bladder wall and the calculi should be performed and appropriate antibiotic therapy administered. The bladder is closed in two layers—a simple continuous and an inverting pattern of absorbable monofilament suture on an atraumatic needle. After surgery, the patient is placed on systemic antibiotics pending results of urine culture. Fluid diuresis is maintained for 24 to 48 hours postoperatively, and the patient is placed on a diet of meat protein and no plant material, the latter of which is believed to predispose to calculus formation in ferrets.2,16 Urinary acidifiers are usually not required if the animal receives a high-quality, meat-based diet. Perineal urethrostomy can be performed in ferrets with urethral obstruction not amenable to medical manage-

ment or in an emergency when urethral catheterization is not possible. The technique is analogous to that performed in cats, but ferret anatomy is smaller. Magnification loupes and microsurgical instruments are essential.

OVARIOHYSTERECTOMY Ferrets are induced ovulators and remain in estrus until stimulated to ovulate by breeding or through artificial means. Female ferrets may remain in estrus for 6 months or more, and the body’s estrogen levels remain high throughout this time.17–19 This chronic hyperestrogenemia results in bone marrow suppression and potentially fatal aplastic anemia.18,19 After 1 month of estrus, female ferrets are considered at risk for developing bone marrow hypoplasia; clinical signs include lethargy, depression, anorexia, hindlimb weakness, pale mucous membranes, and petechial and ecchymotic hemorrhages of the mucous membranes and skin. Female ferrets in estrus may also develop symmetric alopecia accompanied by no other clinical signs. A complete blood count (CBC) reveals severe, nonregenerative, normocytic anemia and frequently demonstrates the presence of nucleated erythrocytes, neutropenia, and thrombo-

PERINEAL URETHROSTOMY ■ HYPERESTROGENEMIA ■ BONE MARROW HYPOPLASIA

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cytopenia. Treatment is aimed at reversing the bone marrow suppression, and ovariohysterectomy should be performed as soon as the patient is stable. Blood transfusions are indicated in ferrets with a hematocrit below 30%. The best prevention is to spay female ferrets at 4 to 6 months of age or within the first 2 weeks of the first estrus. In the United States, most commercially available ferrets are spayed at an early age (i.e., 5 to 6 weeks) before their arrival at pet stores. A CBC and platelet count should be evaluated on all intact female ferrets before performing an ovariohysterectomy to determine whether bone marrow suppression has already occurred.20 Ovariohysterectomy in ferrets is analogous to that in cats, with the ventral midline incision centered midway between the umbilicus and pubis. The uterus is bicornuate, and the ovarian ligament is loose and easily torn.7 Spayed female ferrets that have clinical signs of estrus are usually affected with adrenal neoplasia and rarely have residual ovarian tissue. Female ferrets that have been spayed but that have residual ovarian tissue will generally present with vulvar swelling and signs of estrus at an earlier age (younger than 2 years of age) than will ferrets with adrenal tumors (older than 2 years of age). In most ferrets with active ovarian tissue, vulvar swelling subsides following administration of 100 IU human chorionic gonadotropin, whereas this hormone has no effect in ferrets with adrenal disease.20,21 Although ectopic ovarian tissue has been reported in ferrets, residual tissue is a result of incomplete ovariectomy in most patients.2 The surgical approach used when exploring for residual ovarian tissue is through a ventral midline incision adequate for a complete exploratory celiotomy. The ovarian stumps at the caudolateral pole of each kidney are inspected for evidence of ovarian tissue. The exploration should be thorough even if one section of ovary is found because other remnants may be present. Vulvar swelling generally regresses in 1 to 5 days after removal of the ovarian tissue. Because most female pet ferrets are spayed at an early age, the incidence of pyometra is relatively low. Common isolates include Escherichia coli, Staphylococcus, Streptococcus, and Corynebacterium.17 Polyuria and polydypsia are not common clinical signs in ferrets with pyometra. Hyperestrogenism may occur concurrently, underscoring the need for a preoperative CBC. The CBC is normal in many ferrets, although pancytopenia and neutrophilic leukocytosis may be evident. Surgical and postsurgical management of ferrets with pyometra is similar to that in other species and includes ovariohysterectomy and appropriate antibiotic and supportive OVARIOHYSTERECTOMY ■ RESIDUAL OVARIAN TISSUE

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therapy. In some ferrets with adrenal gland disease, stump pyometra develops.16 Treatment involves appropriate antibiotic and supportive care in addition to surgical removal of the diseased adrenal gland and infected uterine stump.

12.

13.

REFERENCES 1. Mullen HS, Scavelli TD, Quesenberry KE, Hillyer E: Gastrointestinal foreign body in ferrets: 25 cases (1986 to 1990). JAAHA 28:13–19, 1992. 2. Brown SA: A Practitioner’s Guide to Rabbits and Ferrets. Denver, CO, American Animal Hospital Association, 1993, pp 65–90. 3. Hoefer HL: Gastrointestinal diseases, in Hillyer EV, Quesenberry KE (eds): Ferrets, Rabbits, and Rodents Clinical Medicine and Surgery. Philadelphia, WB Saunders Co, 1997, pp 26–36. 4. Brown SA: All those other diseases of the ferret. Proc NAVC:727–729, 1993. 5. Dulisch ML: Gastrotomy, in Borjrab MJ (ed): Current Techniques in Small Animal Surgery, ed 9. Philadelphia, Williams & Wilkins, 1998, pp 205–206. 6. Ellision GW: Enterotomy, in Borjrab MJ (ed): Current Techniques in Small Animal Surgery, ed 9. Philadelphia, Williams & Wilkins, 1998, pp 245–248. 7. Mullen H: Soft tissue surgery, in Hillyer EV, Quesenberry KE (eds): Ferrets, Rabbits, and Rodents Clinical Medicine and Surgery. Philadelphia, WB Saunders Co, 1997, pp 131–144. 8. Orsher RJ, Rosin E: Small intestine, in Slatter D (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders Co, 1993, pp 593–612. 9. Hillyer EV: Working up the ferret with a large spleen. Proc NAVC:819–821, 1994. 10. Hillyer EV: Other diseases—Splenomegaly, in Hillyer EV, Quesenberry KE (eds): Ferrets, Rabbits, and Rodents Clinical Medicine and Surgery. Philadelphia, WB Saunders Co, 1997, pp 72–74. 11. Lipowitz AJ, Blue J: Spleen, in Slatter D (ed): Textbook of

14. 15. 16. 17. 18. 19. 20. 21.

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Small Animal Surgery. Philadelphia, WB Saunders Co, 1993, pp 948–961. Couto CG, Hammer AS: Diseases of the lymph nodes and the spleen, in Ettinger SJ, Feldman EC (eds): Textbook of Veterinary Internal Medicine. Philadelphia, WB Saunders Co, 1995, pp 1930–1946. Evans HE, An NQ: Anatomy of the ferret, in Fox JG (ed): Biology and Diseases of the Ferret, ed 2. Baltimore, Williams & Wilkins, 1998, pp 16–69. Nguyen HT, Moreland AF, Shields RP: Urolithiasis in ferrets (Mustela putorus). Lab Anim Sci 29(2):243–245, 1979. Bell J: Management of urinary obstruction in the ferret. Proc NAVC:724, 1993. Hillyer EV: Urogenital diseases, in Hillyer EV, Quesenberry KE (eds): Ferrets, Rabbits, and Rodents Clinical Medicine and Surgery. Philadelphia, WB Saunders Co, 1997, pp 44–52. Fox JG, Pearson RC, Gorham JR: Diseases associated with reproduction, in Fox JG (ed): Biology and Diseases of the Ferret. Philadelphia, Lea & Febiger, 1988, pp 186–196. Kociba GJ, Caputo CA: Aplastic anemia associated with estrus in pet ferrets. JAVMA 178(12):1293–1294, 1981. Bernard SL, Leathers CW, Brobst DE, Gorham JR: Estrogen-induced bone marrow depression in ferrets. Am J Vet Res 44(4):657–661, 1983. Ryland LM, Bernard SL: A clinical guide to the pet ferret. Compend Contin Educ Pract Vet 5(1):122–129, 1983. Rosenthal KL: Adrenal gland disease in ferrets. Vet Clin North Am Small Anim Pract 27(2):401–418, 1997.

About the Authors Drs. Wheeler and Bennett are affiliated with the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida. Dr. Bennett is a Diplomate of the American College of Veterinary Surgeons.