We present a case of renal abscess with perinephric and paranephric extension. Ultrasonography showed an intrarenal lesion. The extension into the perinephric and paranephric space was better defined on MRI.A 30-year-old woman at 25 weeks gestation was transferred for evaluation of a left renal mass. She presented to the emergency department with a 1-week history of left flank pain, which was exacerbated following a fall. On physical examination, she was afebrile and was markedly tender in the left renal flank.Microscopic urinalysis revealed 10-100 × 10 6 /L white blood cells. There was no bacterial growth on urine culture.Ultrasonography showed a complex, vascular mass measuring 11 × 6.5 cm arising from the mid to lower pole of the left kidney ( Fig. 1).As the nature of the mass was indeterminate, an MRI scan was performed at 27 weeks gestation. Axial T1-weighted gradient echo (Fig. 2a), axial T2 half-fourier acquisition single shot turbo spin echo, coronal T2 turbo spin-echo with fat suppression (Fig. 2b) and 2-D true free induction steady precession of the inferior vena cava (IVC) and renal veins were performed. Magnetic resonance imaging showed an enlarged heterogeneous mass arising from the mid and lower pole of the left kidney measuring approximately 12.0 cm in length, 8.0 cm in width and 8.5 cm in anteroposterior dimension. The mass was of both intermediate-and low-signal intensity in the T1-weighted acquisition and heterogeneous high-signal intensity in the T2-weighted sequences. The left kidney was displaced superiorly and anteromedially, and the tail of the pancreas was displaced anteriorly. There was mild dilatation of the left upper pole collecting system. The left quadratus lumborum and iliopsoas muscle showed high-signal intensity in the axial T2 and intermediate-to low-signal intensity in the T1-weighted sequences. There was loss of the fascial plane between the left renal mass and the paraspinal muscle. The M Puvaneswary MB BS, FRCR; A Bisits MB BS, FRANZCOG, Dip Clin Epi, M Med Stat; B Hosken MB BS, BSc, FRACS.Fig. 1. Ultrasound shows a large heterogeneous mass arising from the mid and lower pole of the left kidney.