Characterization of intramuscular calf vein thrombosis on routine knee MRI

Literature regarding intramuscular calf vein thrombosis (IMCVT) or infrapopliteal deep vein thrombosis (DVT) evaluation by magnetic resonance imaging (MRI) is limited, particularly with regard to routine unenhanced knee examinations. We attempt to correlate routine unenhanced MRI findings with ultrasound evaluations of the lower extremity deep venous system. The radiology information system was searched, yielding a total of 67 patients who had undergone both routine knee MRI and duplex ultrasound examinations within 14 days. The MRI examination findings recorded were the presence and pattern of edema, segmental vein dilation, intraluminal signal on fluid-sensitive sequences, and abnormal hyperintense signal on axial T1-weighted sequences. The presence and extent of thrombus more centrally (i.e., intramuscular calf vein thrombosis with or without extension into the popliteal vein) was reassessed on ultrasound. When comparing patients with positive (n = 13) and negative (n = 54) ultrasound, there were significant differences in each of these parameters: perivascular edema, intramuscular edema, focal vein dilation, and abnormal fluid-sensitive signal. In the subset of patients with popliteal extension of the intramuscular calf vein thrombosis compared with those without any deep vein thrombosis, there was a statistically significant increase in peripopliteal edema, abnormal fluid-sensitive signal, and abnormal hyperintense T1 signal. Imaging findings on routine unenhanced MRI have a high rate of concordance with duplex ultrasound performed through the calf in the detection of intramuscular calf vein thrombosis.