SEARCH

SEARCH BY CITATION

A 17-month-old, spayed female, 32.3-kg (70.9-lb) Labrador Retriever was examined for evaluation of a suspected peripheral arteriovenous malformation of the right rear limb. The owner reported the skin in the inner right thigh had a strawberry color that was present when the dog was adopted at 10 weeks of age. After approximately 6 months, the entire right medial thigh became dark red to black in color, painful to the touch and developed a central area of ulceration which prompted the owner to seek evaluation with the referring veterinarian. The ulcerative lesion was refractory to antimicrobial and nonsteroidal anti-inflammatory medications administered over a 2-month period. The ulcerated mass was surgically removed and histopathology results showed a large tortuous central artery surrounded by smaller veins and capillary proliferation typical of an arteriovenous fistula. The dog was referred for diagnostic evaluation and possible surgical removal of the suspected fistula 3 months after the biopsy was obtained.

A large swollen hyperemic lesion with a central area of ulceration was present from the right inguinal area to the mid-stifle. The area was hyperthermic and painful to the touch, and the right inguinal lymph node was palpably enlarged. A bruit was audible over the right medial thigh without a palpable thrill, and the right femoral arterial pulse was bounding (“water hammer”) while the left femoral arterial pulse was normal. No cardiac murmur or arrhythmia was ausculted. The remainder of the exam was unremarkable. Complete blood count, biochemistry panel, electrolytes, and coagulation panel (prothrombin time, partial thromboplastin time, antithrombin III) were within normal limits. Echocardiographically, the heart size and function were normal with no evidence of volume overload. Ultrasound examination of the right medial thigh showed an enlarged artery at the level of the patella, evidence of venous distension and inguinal lymph node enlargement. A radiopaque rulera with metallic markers at 1 mm increments was adhered externally to the limb at the level of the suspected arteriovenous fistula as a fluoroscopic landmark.

The dog was premedicated for contrast angiography with a combination of hydromorphone (0.05 mg/kg [0.02mg/lb] SC) and glycopyrrolate (0.01 mg/kg [0.005 mg/lb] SC). Anesthesia was induced with propofol (2.8 mg/kg [1.3 mg/lb] IV) and maintained with sevoflurane. An incision was made over the right carotid artery and once isolated, a 7F introducerb was placed using a modified Seldinger technique. A 6F Bright Tipc guiding catheter was advanced to the bifurcation of the descending aorta using a 0.035-in. J-tipped guide wire.d An angiogram was performed and the guide wire was advanced into the right femoral artery toward the region of the suspected arteriovenous fistula. The guide wire and catheter were advanced into the right femoral artery and a selective angiogram performed showing a spider web of vessels and blushing into the soft tissue structures in the area corresponding to the swelling in the inguinal area. The guide wire was advanced subsequently into the right saphenous artery and a selective angiogram performed showing the precise location of the arteriovenous fistula (Fig 1), multiple tortuous arteries, and premature filling of the veins. The arterial side of the fistula measured 1.8 mm in diameter. A single 0.035 in., 3-mm diameter, 5-cm length Gianturco coile was deployed. After deployment of the coil, the catheter was withdrawn into the femoral artery and a selective angiogram documented complete occlusion of the arteriovenous fistula (Fig 2). A total of 1.7 mL/kg of nonionic, low osmolality iodinated contrast agentf was administered via hand injection pre and postocclusion. The dog recovered uneventfully with immediate resolution of the bruit. Aerobic culture of the ulcerative lesion submitted 2 weeks before the procedure isolated Pasteurella multocida and Staphylococcus intermedius and no growth of fungal organisms at 23 days. Based on sensitivity results, the dog was administerd cephalexin (31 mg/kg [14.1 mg/lb] PO q12h for 14 days). At 1 week after the procedure, the dog was no longer painful and at 2 weeks the ulcerative lesion was completely healed. At 6 weeks the lymph node remained swollen, but had decreased to less than half of it size and swelling in the surrounding tissue had resolved. At 16 weeks, the inner thigh had returned to normal while the original strawberry-colored markings remained.

image

Figure 1.  Selective angiography of the right femoral artery demonstrating a congenital arteriovenous fistula of the saphenous artery with multiple tortuous arterial vessels (A) and shunting of contrast into the venous system (B).

Download figure to PowerPoint

image

Figure 2.  Following coil embolization, a selective angiogram of the femoral artery demonstrates complete occlusion of the fistula.

Download figure to PowerPoint

Discussion

  1. Top of page
  2. Discussion
  3. Footnote
  4. References

An arteriovenous fistula is an abnormal communication between an artery and a vein that can be congenital or acquired.1 Congenital arteriovenous fistulas are caused by a failure of embryologic vasculature to differentiate into arteries and veins resulting in persistent arteriovenous communication and have been reported in the liver, orbit, and extremities in dogs.2–4 Acquired arteriovenous fistulas are reported with more frequency and are often associated with trauma or surgical procedures.5,6 Although the dog in this report had an unknown history before being adopted by the owner, the young age combined with the progressive nature of the lesion suggested the arteriovenous fistula most likely had a congenital origin.

The abnormal vascular communication that occurs with an arteriovenous malformation allows blood to follow the path of least resistance from the high-pressure arteries to the low-pressure veins resulting in increased venous pressure and decreased distal perfusion.2 The resulting increase in pressure and volume causes compensatory hypertrophy and dilation of the veins depending on the relative size of the fistula. Blood flow to the arteries distal to the fistula may be compromised and as perfusion diminishes, localized swelling, ischemia, and ulceration may occur. Affected tissue may develop hyperemia and hyperthermia due to the development of extensive collateral circulation. Tissue swelling, ischemia, ulceration, and possibly compression of nervous tissue contribute to pain. Skin discoloration resembling a birth mark may be observed in early lesions. The turbulent blood flow within the veins can produce an audible murmur, often called a bruit. An increase in systolic pressures with rapid diastolic run-off into the venous system results in bounding pulses. In cases with large volumetric shunting, the cardiovascular system becomes volume overloaded resulting in cardiomegaly and congestive heart failure. The dog in this report had signs at the location of the arteriovenous fistula that included hyperemia, hyperthermia, swelling, skin ulceration, bruit, and bounding pulses but systemic signs of volume overload were not evident. Inguinal lymph node enlargement was attributed to inflammation associated with the skin lesions.

Arteriovenous fistulas can be challenging to diagnose and treat. Ultrasonography, computed tomography and magnetic resonance imaging provide information regarding the anatomy and location of the fistula.3,7 Angiography is essential for determining the precise location of the fistula. Angiographic findings classic for arteriovenous fistula include enlarged, tortuous arteries and premature filling of the veins. During angiographic studies of the dog of this report, blushing of contrast into multiple web-like vessels occurred proximal to the fistula where the tissue was swollen; and ultrasound-guided external placement of a radiopaque measuring device at the level of the fistula was useful for isolating the exact location near the patella during fluoroscopy. Fistulas that demonstrate progressive enlargement and local or systemic affects require surgical removal or interventional closure techniques. If the vascular malformation is too large for surgical removal, percutaneous embolization may diminish the size enough to allow successful surgical removal.7 Percutaneous embolization of cyanoacrolate into the arteriovenous fistula of the antebrachium in a cat allowed for complete surgical excision.7 Percutaneous embolization is a minimally invasive procedure where occlusion coils or other materials can be precisely delivered to the vascular lesions. Coils have been successfully utilized for occlusion of vascular anomalies including patent ductus arteriousus, portosystemic shunts, and orbital varix.8,9,g Potential complications of embolization therapy include inappropriate embolization and incomplete occlusion. Recanalization and development of collateral circulation can cause recurrence of arteriovenous shunting. In humans, the success of embolization therapy is dependent on the underlying cause (congenital or traumatic) and the presence of single or multiple fistulous vessels.10 Two dogs in a prior report of successful coil embolization of arteriovenous fistulas redeveloped flow within the fistula within 8 weeks.h The dog in this report had a single congenital arteriovenous fistula which may have been the reason complete occlusion with a single coil was successful. Skin ulceration and pain resolved within 2 weeks and swelling of the lymph node and surrounding tissue had resolved by 16 weeks following coil embolization.

Footnote

  1. Top of page
  2. Discussion
  3. Footnote
  4. References

aStent guide—radiopaque marking tape, Infiniti Medical, Malibu, CA

bIntroducer, Boston Scientific, Natick, MA

cVista Bright tip catheter, Cordis, Warren, NJ

dGlidewire, Terumo Medical Corporation, Somerset, NJ

eGianturco Embolization coils, Cook Inc, Bloomington, IN

fOxilan, Cook Inc

gWeisse C, Berent A, Elville K, et al. Coil embolization of canine intrahepatic shunts: 42 cases. J Vet Intern Med 2006;20:753 (abstract)

hFox PR, Keene BW, Gordon S et al. Transarterial closure of arteriovenous fistulas: methods and outcome in three cats and two dogs. J Vet Intern Med 2002;16:341 (abstract)

References

  1. Top of page
  2. Discussion
  3. Footnote
  4. References