Lump in my side: transplanted kidney or something more?

A 16-year-old girl with a background of systemic lupus erythematosus (SLE) and resultant end-stage kidney disease (ESKD) presents 1 month post deceased donor kidney transplantation with fever, abdominal pain, back pain and arthralgias.Her temperature was 39.3C, heart rate 100 bpm and blood pressure 116/65 mm Hg.Her abdomen was soft with normal bowel sounds but had tenderness in her right lower quadrant on deep palpation overlying her allograft site.The rest of her examination was unremarkable.Initial investigations revealed a new normocytic normochromic anaemia (haemoglobin: 95 g/L), acute kidney injury (serum creatinine increased to 82 umol/L from a baseline of 50-60 umol/L) and elevated C-reactive protein (58.6 mg/L).A transplant kidney ultrasound (figure 1) was performed, showing a new lateral perinephric complex cystic fluid collection.An abdominal MRI (figure 2) was done, showing a lateral septated cystic lesion (2.44.23.6 cm) and an anteromedial ill-defined heterogeneous mass (72.98.3 cm) associated with inflammatory changes.