A 60-year-old male presented with left flank pain and weight loss. Because of clinical suspicion of urolithiasis the patient was referred for imaging. On clinical examination there was no flank tenderness. A few enlarged cervical and inguinal lymph nodes were found.
Clinical and Laboratory Evaluation: Routine urine analysis showed albuminuria 2+, numerous leucocytes in urine and negative nitrite test. On urine microscopy 227 RBCs/hpf, 314 WBCs/hpf and 239 bacteria/hpf were found (hpf = high power field). However, there was no growth on bacterial culture. This was indicative of sterile pyuria. A diagnosis of renal tuberculosis was considered with a differential diagnosis of chronic pyelonephritis.
Initial evaluation on plain CT showed disproportionately dilated upper pole calyces and urothelial thickening with narrowing of the pelvis with papillary calcifications in the lower pole. Significant perinephric and periureteric fat stranding with locoregional lymphadenopathy was noted (Figure 1). This was followed up by a CT urogram. CT urogram showed multiple filling defects within the calyceal system with a papillary cavity in the upper and lower poles with calyceal distortion and infundibular-pelvic stenosis. Also, the ureter showed thickened and enhancing walls (Figure 2). The features of disproportionate calyceal dilation with papillary cavities, infundibular-pelvic stenosis and calcifications with necrotic locoregional adenopathy are suggestive of an infective aetiology such as tuberculosis. Other signs of papillary necrosis such as blunt-tipped calyces and a ring sign:where contrast is seen surrounding a centrally non-opacified calyx:are seen (Figure 3). This was followed by a static MR urogram to show that the findings demonstrated on a CT urogram with contrast administration could also be demonstrated without contrast administration on an MR urogram. The following MR sequences were used:axial 2D FIESTA FATSAT (TR 3.60 ms, TE 1.55 ms. Slice thickness 8 mm, ET 1, matrix size 320 x 224), Coronal 2D FIESTA FATSAT (TR 3.60 ms, TE 1.56 ms. Slice thickness 5 mm, ET 1, matrix size 192 x 288), 3D magnetic resonance cholangiopancreatography (MRCP) RTr ASSET (TR 3750 ms, TE 383 ms. Slice thickness 1.6 mm, ET 64, matrix size 256  x 256), diffusion-weighted imaging axial (TR 6250 ms, TE 93.50 ms. Slice thickness 8 mm, ET 1, matrix size 128  x 128), diffusion-weighted imaging coronal (TR 5825 ms, TE 92.20 ms. Slice thickness 5 mm, ET 1, 128 x 128) and thick slab MRCP ASSET coronal sequence(TR 2566 ms, TE 1202 ms. Slice thickness 60 mm, ET 1, 384 x 256). MR urogram showed the filling defects within the calyces including the signs of papillary necrosis found on the CT urogram such as calyceal filling defects, blunt-tipped calyces, the ring sign and clefts (Figure 4). Thick and thin slab 3D MRCP sequences showed the calyceal findings of papillary necrosis with a dilated ureter with narrowing at its insertion suggestive of a stricture. The distal ureteric stricture was seen better on MRI (Figure 5).