MRI
There is a well-defined lobulated soft tissue mass involving the anterior and posterior recesses of the ankle joint; the bulk of the lesion is seen anteriorly with syndesmotic extension through the anterior tibiofibular ligament and intra-osseous extension to the medial tibial epiphysis.
The mass displays intermediate to low signal on T1 WI, low signal on T2 WI, heterogeneous high signal on STIR, and avid enhancement on the post-contrast study with susceptibility artifact on gradient sequence.
The mass is deep to the ankle extensor tendons and pushes them anteriorly.