An 11-year-old Greyhound presented with progressive lameness/paraparesis of a few months duration - see Video 1. The dog had become acutely worse in the last 2 weeks. Neurological examination revealed normal proprioception in all 4 limbs. Pain on minimal hind limb extension. There was no stifle nor hock instability.
On physical examination, the dog had an absent femoral pulse in both hindlimbs suggestive of ischemic neuromyopathy.

MRI of the lumbar spine and CT of the thorax and abdomen were performed. From the CT post-contrast on the angiography (arterial) phase there was a contrast-filling defect caused by a soft tissue lesion within the caudal abdominal aorta, from the level of the caudal aspect of L5 and filling most of the lumen of the aorta, representing a thrombus (See Figure 1). This extended for a length of 6 cm into the aorta caudally continuing into the external iliac arteries bilaterally and into the femoral arteries. The aortic thrombus was also visualized from the MRI images provided to us, as an intraluminal lesion of heterogeneous signal intensity, predominantly hyperintense in T2W and T1W (See Figure 2). No intramedullary, extradural, or intradural lesions were seen affecting the spinal cord. From the CT study, the left hind limb muscles showed a heterogeneous appearance, characterized by multiple ill-defined hypoattenuating lesions, likely representing ischaemic myopathy. No other thoracic or abdominal lesions were present.

The owner declined further investigations to look for causes of hypercoagulability. Various treatment options were also discussed including surgical intervention (open surgical thrombectomy vs. interventional thrombectomy) vs. placement of an indwelling catheter in the aorta to treat locally with TPA for 24-48 hours vs. conservative management with oral anticoagulants. The owner elected for the latter. The dog was treated with rivaroxaban and clopidogrel for 2 weeks and clopidogrel alone for a further 4 weeks. Video 2 shows the dog on re-evaluation at 6 weeks. Click on the images to expand them into full view.

Aortic thrombosis (ATh) is an uncommon condition in dogs, thought to be associated with a regional prothrombotic environment in the distal aorta. This is in contrast to aortic thromboembolism (ATE) in cats, where thrombi formed in the left atria or auricle embolize to the aorta. The clinical presentation in dogs with ATh is in the large majority of cases chronic manifesting as a gradual onset of clinical signs in contrast to the thromboembolic disease seen in cats causing acute onset. For more information click on the button below.

Courtesy of Dr. Kenny Carroll from Veterinary Specialists of Sydney (VSOS).