These myxomas most frequently occur in the subcutaneous fat of knee, but can also arise anywhere in the intra- and extracapsular spaces. While benign, a recurrence rate of ~30% has been reported.
In contrast to the more common intramuscular myxomas, which have homogenous low signal intensity on Tl-weighted images and homogeneous high signal intensity on T2-weighted images, juxta-articular myxomas are more likely to be heterogeneous and have myxoid degeneration.
The case above is a juxta-articular myxoma arising in posterior suprapatellar fat pad. The lesion is cystic on ultrasound. T1-FS images reveals a lesion that is isointense to muscle and has mild peripheral enhancement. No other sequences were available.
The main differential consideration in this case is a ganglion cyst. Ganglion cysts have myxoid tissue that is much less developed than in juxta-articular myxomas and are typically smaller.
- Daluiski A, Seeger LL, Doberneck SA, Finerman GA, Eckardt JJ. A case of juxta-articular myxoma of the knee. Skeletal Radiol. 1995 Jul;24(5):389-91.
- Kosty JW, Moore JG. Juxta-articular myxoma within the suprapatellar pouch masquerading as a ganglion cyst. Orthopedics. 2009 Jul;32(7):527.