Left popliteal mass A complex predominantly cystic mass is noted within the posterolateral compartment of the leg lying below the fascial plane of the medial head of the gastrocnemius. There is mass effect upon the muscle itself but no direct invasion. The mass measures approximately 18 cm in the craniocaudal dimension and is heterogeneous in signal on both T1 and T2 sequences. The more superior aspect of the mass is heterogeneous in nature but contains a large T1 hyperintense component likely reflecting hemorrhagic contents. There is soft tissue enhancement both proximal and distal to the mass although there is no discrete nodular enhancement of the mass itself. The marrow signal of the tibia and fibula there is normal. The remaining muscles are normal in caliber and signal as well.
Large complex hemorrhagic mass within the posterior lateral component of the leg. This could represent an old hematoma with other differentials including complex Baker's cyst and or discrete soft tissue mass are also possible but thought to be less likely.