MAGNETIC RESONANCE IMAGING
The use of MRI to diagnose hepatic vascular anomalies is not established in veterinary medicine. Magnetic resonance angiography
(MRA) has been described as a noninvasive technique for imaging portal vasculature.32,33
One study reports 80% sensitivity and 100% specificity for the diagnosis of any shunt type, and 63% sensitivity and 97% specificity
for the diagnosis of multiple extrahepatic portosystemic shunts.32 Smaller vessels may not emit a detectable signal, making it difficult to diagnose multiple acquired shunts or some smaller
single extrahepatic portosystemic shunt by using MRA.32
Figure 12 depicts a portoazygous shunt detected by MRA.
Figure 12. MRA of an extrahepatic portosystemic shunt. This sagittal MRA image of a dog with a single extrahepatic portosystemic
shunt shows contrast enhancement of a portoazygous shunt. The dog’s head is to the left. (Figure 12 courtesy of the Department
of Veterinary Clinical Sciences at Washington State University.)
Image acquisition times are longer for MRI than for CT, resulting in lengthened anesthetic periods for patients undergoing
MRI. A more recent study on contrast-enhanced MRA used nonselective angiography, which reduced acquisition time but made interpretation
more complicated by enhancing all abdominal vasculature.33 To date, no advantage to the use of MRA vs. CT angiography has been established.
A variety of diagnostic imaging modalities have been described to evaluate hepatic vascular disease. The ideal method will
provide a high degree of sensitivity and specificity and fine resolution for detailed anatomic reconstruction and be both
affordable and available while presenting minimal risk to patients. Our ability to characterize hepatic vascular diseases,
obtain early diagnoses, formulate therapeutic plans, and provide prognostic information will expand as advanced diagnostic
imaging techniques are applied to these diseases with greater frequency.
To view the references for this article, visit
Valerie L. Case, DVM, DACVIM
Center for Veterinary Specialty Care
1712 Frankford Road, Suite 108
Carrollton, TX 75007
Brian C. Norman, DVM, DACVIM
Veterinary Specialists of the Valley
22123 Ventura Blvd.
Woodland Hills, CA 91364
Jason Francis, DVM, DACVR
Ventura Veterinary Imaging Specialists
4221 E. Main St.
Ventura, CA 93003