(99m)Tc-DTPA diuretic renal scintigraphy in cats with nephroureterolithiasis

Abstract

The purpose of this study was to evaluate results of diuretic renal scintigraphy in 32 feline kidneys with nephroureterolithiasis and variable degrees of renal pelvis/ureteral dilation. Six kidneys showed a non-obstructive scintigraphic pattern, with a downward slope of time-activity curves (TAC) and a median excretion half-time of radiopharmaceutical (T((1/2))) of 6.09 (5.08-8.43) min. Eight kidneys showed an obstructive pattern, with a continuous rise of TAC and median T((1/2)) of -7.91 (-43.13-0.00) min. In one kidney with presumptive partial obstruction scintigraphic results were equivocal. Seventeen kidneys, most of which had an individual kidney glomerular filtration rate below 0.5ml/min/kg, had non-diagnostic studies. Diuretic renal scintigraphy may be a useful adjunct modality in the diagnosis of ureteral obstruction in some cats if renal function is maintained. However, the large number of non-diagnostic studies in animals with decreased renal function represents a clear limitation of the technique.

Fig 1

Non-obstructive nephrolithiasis in a 5-year-old domestic shorthair cat. (A) Ultrasonographic image shows a linear hyperattenuating structure with distal sound beam attenuation (between cursors) associated with the left kidney. The kidney (between arrowheads) is small and has a triangular hyperintense area associated with the cranial pole, consistent with an infarct. There is no evidence of renal pelvis dilation. (B) TAC derived during diuretic renal scintigraphy. Furosemide was injected at 4.5 min (arrow). Gradual and continuous down slope of the curve following administration of furosemide is consistent with a non-obstructive pattern (T_½=8.54 min).

Fig 2

Obstructive ureterolithiasis in a 4-year-old cat. (A) Lateral abdominal radiograph shows small size and irregularity of the right kidney, bilateral renal mineralization and a small mineral opacity in the plane of the retroperitoneal space (arrow), consistent with an ureterolith. (B) Transverse ultrasonographic image of the left kidney shows mild renal pelvis dilation (between cursors) and a small non-obstructive nephrolith. At this point, there was no evidence of hydroureter. (C) TAC derived during diuretic renal scintigraphic study on the same day. Furosemide was injected at 4.5 min (arrow). Continuous rise of the curve following administration of furosemide is consistent with an obstructive pattern (T_½=−31.35 min). (D) Recheck ultrasound 2 days later demonstrates progressive renal pelvis dilation (between cursors), consistent with scintigraphic diagnosis of obstruction. Hydroureter was also noted at this time.

Fig 3

Suspected partial ureteral obstruction in a cat. (A) Initial scintigraphic study shows only mild down slope of TAC following injection of furosemide (T_½=13.99 min), which is considered equivocal for obstruction. (B) Repeat diuretic renal scintigraphy 1 month later demonstrates an obstructive pattern, with continuous rise of TAC. (C) Diuretic renal scintigraphy after lithotripsy is consistent with a non-obstructive pattern (T_½=5.08 min). (D) Recheck scintigraphy 1 month later still shows a non-obstructive pattern (T_½=5.35 min).

Fig 4

Diuretic renal scintigraphy curves from a cat with bilateral ureterolithiasis, hydronephrosis and hydroureter. The cat was azotemic at presentation (BUN 72 mg/dl; serum creatinine 5.8 mg/dl). The curve for the left kidney was considered non-diagnostic, while the curve for the right kidney was consistent with obstruction. Individual kidney GFR as determined by scintigraphy was 0.17 ml/min/kg for the left kidney and 0.57 ml/min/kg for the right kidney. Low total GFR (0.74 ml/min/kg) is consistent with azotemia. The majority of total renal function (77%) was derived from the right kidney, and renal function on this side was still sufficient to generate a diagnostic curve. The cat underwent surgical exploration, and right-sided ureteral obstruction was confirmed.