A case report of renal papillary necrosis due to tuberculosis—CT urogram and static MR urogram findings

The urinary tract is a common site of tuberculosis, which causes significant morbidity in the form of chronic renal disease. T uberculosis is not only common in developing countries but with the spurt in the number of immune-suppressed patients and the increasing incidence of drug -resistant strains, an increase in the number of patients suffering from genitourinary tuberculosis is expected even in developed countries. Genitourinary tuberculosis occurs owing to haematogenous dissemination of tubercular bacilli. Urinary tract tuberculosis can result in complications such as ureteric stricture, chronic pyelonephritis and papillary necrosis, resulting in compromised renal function. This renal compromise makes it prudent to avoid contrast- enhanced studies if other alternatives are available. There is a dearth of-cases of papillary necrosis reported on static MR urogram. The authors report a case of tuberculosis complicated by papillary necrosis on both CT urogram and static MR urogram.


BACKGROUND
Urogenital tuberculosis is the most common cause of extrapulmonary tuberculosis, affecting about 27% of patients suffering from it. 1 Tuberculosis is not only common in developing countries; but with the spurt in the number of immune-suppressed patients and the increasing incidence of drug-resistant strains, an increase in the number of patients suffering from genitourinary tuberculosis is expected even in developed countries. 1 Genitourinary tuberculosis occurs owing to haematogenous dissemination of tubercular bacilli. 1,2 Discussed below is a patient from a low socioeconomic background who presented for evaluation of flank pain and weight loss. It is important to suspect and diagnose tuberculosis on imaging to direct the clinician to perform appropriate investigations such as culture for Mycobacteria. Appropriate treatment is necessary to prevent complications such as ureteric strictures, putty kidney, thimble bladder and tubercular renal abscesses.
Many patients with renal tuberculosis have compromised renal function. This makes it prudent to avoid the use of contrast in such patients. This case report aims to show that static MR urogram can be used to make the diagnosis of renal tuberculosis without the risks of contrast or radiation dose administration. This case report describes the findings of renal tuberculosis with papillary necrosis on static MR urogram.

CLINICAL PRESENTATION
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.

IMAGING
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 Â 224),    ET 1,384 Â 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).

DISCUSSION
The most common extrapulmonary site of tuberculosis is the urinary tract, with almost all cases resulting from haematogenous seeding. Despite the presumed route of spread from the lungs to the kidney, less than half the patients who have genitourinary tuberculosis have abnormal chest radiographs. 2 The tubercular bacilli form granulomas within the kidney and remain indolent for many years. Tuberculosis has a predilection for the upper and lower poles of the kidney. Imaging findings of renal tuberculosis result from the combination of papillary necrosis and parenchymal destruction. These papillary lesions caseate and cavitate, forming ulcerocavernous lesions as they erode into the pelvicalyceal system. Extensive papillary necrosis may develop with the formation of cavities and destruction of the renal parenchyma. They may also rupture into the collecting system, or cause parts of the papillae to become necrotic and slough. The collecting system shows thickening, ulceration and fibrosis, often with stricture formation. Along with papillary necrosis, the above spectrum is highly suggestive of tuberculosis. [3][4][5] In a comprehensive review of the pathophysiology and imaging of renal tuberculosis, Merchant et al 3,5 stated that pelvicinfundibular strictures, papillary necrosis, cortical low-attenuation masses, scarring and calcification may be seen in other conditions, but the combination of three or more of these