CT/MRI
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8-year-old MC Domestic Shorthair Cat

January 7, 2020
Marie de Swarte DVM DipECVDI DACVR University of Tennessee College of Veterinary Medicine

Progressive non-painful right forelimb swelling

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CT venous phase, bone window, MIP, sagittal reconstruction

History

  • The patient first developed non-painful swelling and scabs on the right front foot 3 months ago, which were treated by the primary veterinarian with corticosteroids. Following the absence of improvement, the patient was treated for a potential spider bite injury 2 weeks later without success. The patient was then referred for further investigation.
  • 2-3 days prior to presentation, the swelling of the right front limb markedly increased in severity and a non-weight bearing lameness developed.
  • Upon presentation, on physical examination, the patient had scabs and swelling of the right forelimb. A pulse could be palpated over the front of the limb and blood flow was auscultated. A grade 3/6 heart murmur was also present. An echocardiogram showed an increased left atrial pressure, increased turbulences out of the left ventricular outflow tract with mildly increased velocities and a mild mitral valve regurgitation. Bloodwork did not reveal any significant abnormalities.

CT angiography, right forelimb: arterial phase, soft tissue window

CT angiography, right forelimb: venous phase, bone window

  • Study performed:
    • Dual-phased CT angiogram of the forelimbs using a test bolus technique.
  • Findings:
    • Moderate diffuse swelling of the right forelimb, from the level of the elbow joint to the digits.
    • No osseous abnormality identified.
    • Arterial phase:
      • Concurrent arterial and venous contrast enhancement of the right forelimb.
      • Moderate dilation of the arteries starting at the right subclavian artery.
      • Moderate dilation of the veins with very strong homogeneous contrast enhancement.

From the level of the elbow distally, arteries form a complex plexus of small vessels surrounding the veins of the antebrachium and paw.

  • Normal arterial enhancement pattern of the left forelimb without evidence of venous enhancement.
  • Venous phase:
    • Decreased but persistent strong contrast enhancement of the arteries and veins of the right forelimb with similar changes to the arterial phase.
    • Normal venous enhancement pattern of the left forelimb.
    • Absence of the left internal jugular vein cranial to the thoracic inlet.
  • Marked enlargement with moderate homogeneous contrast enhancement of the right superficial cervical lymph node and moderate enlargement with moderate homogeneous contrast enhancement of the right axillary lymph nodes.
  • Moderately contrast enhancing, ill-defined, 0.6 cm nodule in the dorsal aspect of the cranial subsegment of the left cranial lung lobe.
  • Ground glass opacities to alveolar pattern of the ventral aspects of the cranial lung lobes.
  • Conclusions:
    • Complex right forelimb arteriovenous fistulas with secondary edema and reactive right superficial cervical and axillary lymphadenopathy. Given the history and age of the patient, an acquired etiology is considered most likely.
    • Aplasia of the left internal jugular vein.
    • Left cranial lung lobe nodule could represent a granuloma or a focus of pneumonia. A neoplastic process is considered less likely. Partial atelectasis of the cranial lung lobes.
  • Outcome/Follow up:
    • The right forelimb was amputated the day following the CT study. The patient recovered without complications.
    • The day following the surgery, the heart murmur was still noted but appeared softer.
    • The patient was discharged one day following surgery and was lost from follow-up.
    • The axillary lymph nodes were sent for histopathology and were considered reactive.
  • Arteriovenous fistulas (AVF) are uncommon, symptomatic, vascular communications between an artery and a vein, bypassing the terminal capillary circulation. They can be classified as either congenital (and known as arteriovenous malformations) or acquired, and as either cardiac or extracardiac (peripheral). Congenital arteriovenous malformations are the result of persistent embryological communications between arteries and veins. The most common peripheral congenital arteriovenous malformations in small animal occur in the liver of dogs but have been reported at various other sites. Acquired AVF can be the results of trauma, infection or neoplasia. Cases of iatrogenic AVF have been reported in the veterinary literature following surgery (e.g., declawing, en bloc ligation of an artery and vein), catheterization, venipuncture, extravasation of irritant medications. Locations of reported peripheral AVF are various and include pads, subcutaneous tissues, prepuce, inguinal area, and intestine.
  • Due to the direct connection between the high-pressure arterial system and the normally low-pressure venous system, AVF causes localized hypertension, volume overload and turbulent flows, which in turns lead to vascular remodeling and a progressive increase of the number and size of anastomotic vessels. These vessels often provide an inadequate blood supply to the area leading to variable clinical signs. If the AVF are large, an increase in heart rate and stroke volume may also be detected and is thought to help maximize cardiac output and maintain arterial pressures but may lead to high-output cardiac failure The cardiac changes seen in our patient were believed to be secondary to the AVF fistula.
  • On physical examination and as seen in our case, they may result in the affected region appearing swollen or edematous. Other common skin lesions include non-healing ulcers and thick crusts on the dorsal aspect of the affected paw. Cyanosis and hypothermia of the area distal to the AVF can also be seen. A dilated, palpably pulsatile vessel which may bleed easily can be identified, and occasionally, multiple, tortuous dilated veins under the skin. On auscultation of the area, a continuous murmur, or bruit, and a palpable thrill can be noted. Compression of the proximal artery may induce bradycardia (Nicoladoni-Israel-Branham sign).
  • Survey radiographs of the affected area are usually unhelpful. Doppler ultrasonography may be diagnostic but is considered less sensitive than contrast angiography using fluoroscopy (with digital subtraction) or CT. On Doppler ultrasonography, a tortuous plexus of vessels with pulsatile flow can be detected. As seen in our case, contrast angiography may reveal the presence of a large network of vessels which are impossible to individualize. The vessels may be tortuous and additional abnormal plexuses of vessels may be present distal to the malformation. The advantage of CT is to offer 3D image analysis of the AVF which may help surgical planning.
  • Treatment is surgical and involves complete closure or removal of the AVF. Embolization techniques using cyanoacrylate infusion have also been described.