Fig. 1

Magnetic resonance imaging. a Proton density fat-saturated cross-section showing a lesion projecting on to the upper outer quadrant of the patient’s popliteal fossa, a rounded area of high signal intensity and a few thin septa. b Proton density fat-saturated coronal section showing a lesion projecting on to the upper outer quadrant of the popliteal fossa, a heterogeneous area of high signal intensity and a few thin septa. c Proton density fat-saturated sagittal section showing a lesion projecting on to the upper outer quadrant of the popliteal fossa, a heterogeneous oblong area of high signal intensity and a few thin septa. d Coronal T1 sequence after gadolinium injection showing peripheral contrast enhancement and septa at the upper outer quadrant of the popliteal fossa. e Sagittal T1 sequence after gadolinium injection showing peripheral contrast enhancement and septa at the upper outer quadrant of the popliteal fossa