“A 40-year-old female with painless, slow growing prepatellar mass”

A 40-year-old woman from India presented with a mass in the front of her left knee which had been present for 8 months. Local examination revealed a globular mass of approximate size 5 cm × 4 cm × 4 cm in front of the lower pole of left patella. The patient was investigated with imaging studies and laboratory tests. Plain radiograph of the chest was normal. In addition, contrast enhanced Magnetic Resonance Imaging (MRI) of the left knee was performed. Based on the history, physical examination, laboratory and imaging studies, what is the differential diagnosis?