Presentation
Knee pain, occurred once before 6 months previously, now presenting with acute pain.
Patient Data
MR angiogram of knee was correlated with plain CT and targeted Doppler interrogation.
A tuft of arteriovenous malformation is seen in popliteal fossa with direct arterial feeders from popliteal artery as well as epiphyseal and metaphyseal arteries of distal femur. Venous drainage is through direct and indirect tributaries into popliteal vein. The malformation 'lights up' as early as the second phase of angiogram. The largest nidus is just popliteal vessels measuring 4.0 x 2.8 cm in maximum dimensions. The second largest is seen abutting posterior metaphyseal cortical margin measuring 2.2 x 1.5 cm in maximum dimensions. Serpentine dilated sac abuts posterior distal femoral metaphyseal cortex with areas of chronic extrinsic pressure imprints causing cortical thinning and at certain sites cortical break. There is erosion and loss of approximately 50 % of superior half of lateral femoral condyle.
Menisci
CT correlation reveals the chronicity of the lesion, the pressure changes that led to bony erosions in distal femur.
Doppler study identifies the yin-yang sign with clear arterial feeder and venous tributary off the nidus.
Case Discussion
When I reviewed the radiograph (not included) I was wondering what lesion could have both benign intramedullary margins and at the same time an aggressive cortical margin. High flow vascular malformations can result in pressure necrosis of bone. Another theory is that the large volume of blood being shunted directly bypasses the bone, resulting in less nutrition and secondary avascular necrosis.