Renal accumulation of 99mTc-DMSA in the artificially perfused isolated rat kidney

Differential uptake of Tc-99m DMSA and Tc-99m EC in renal tubular disorders: Report of two cases and review of the literature

Tc-99m DMSA and Tc-99m EC studies are invaluable functional imaging modalities for renal structural and functional assessment. Normally, the relative renal function estimated by the two methods correlates well with each other. We here present two patients with renal tubular acidosis who showed impaired/altered DMSA uptake with normal EC renal dynamic study depicting the pitfall of DMSA imaging in tubular disorders. The two presented cases also depict distinct pattern of Tc-99m DMSA scintigraphic findings in patients with proximal and distal renal tubular acidosis, thus highlighting the factors affecting DMSA kinetics.

Decreased renal uptake of (99m)Tc-DMSA in patients with tubular proteinuria

Although technetium-99m-dimercaptosuccinic acid ((99m)Tc-DMSA) renal scans are widely used to evaluate renal tubular mass function, the mechanism by which renal uptake of DMSA occurs is still the subject of debate. Patients with various proximal tubular disorders show markedly decreased renal DMSA uptake, even when there is normal creatinine clearance. We measured the renal uptake of (99m)Tc-DMSA 3 h after its injection in 13 patients with Dent disease or Lowe syndrome, both of which are typical proximal tubular disorders with defective megalin and cubilin-mediated endocytosis. Serial images of three patients were also obtained at 0.5, 1, 2 and 3 h post-injection. The correlations between renal uptake of (99m)Tc-DMSA and creatinine clearance and the degrees of acidemia and tubular proteinuria were then evaluated. The renal uptake of (99m)Tc-DMSA was markedly decreased in all patients, and the decreased uptake was detected in all serial images. In contrast, bladder radioactivity was higher than normal in all of the serial images when compared to renal radioactivity. Additionally, the uptake of (99m)Tc-DMSA was inversely proportional to the amount of urine beta(2)-microglobulin. These results strongly suggest that DMSA is filtered in the glomeruli and subsequently undergoes megalin- and cubilin-mediated endocytosis in the proximal tubules.

Anionic and cationic drug secretion in the isolated perfused rat kidney after neonatal surgical induction of ureteric obstruction

OBJECTIVE

To study the pathophysiological changes of renal tubular drug transport mechanisms in congenital renal obstruction, by developing a model for perfusing the isolated kidney (IPK) after neonatal surgical induction of partial ureteric obstruction in Hanover Wistar rats.

MATERIAL AND METHODS

Moderately severe obstruction of the right kidney of male rats was created by burying a segment of the right ureter under the psoas fascia at 5-7 days after birth. Different fluorescent substrates for renal organic anion and cation drug transport systems were added to the IPK, and the concentration of these substances with time analysed in perfusate and urine.

RESULTS

The reproducibility in all groups of the glomerular filtration rate (GFR) and drug excretion was remarkably good. GFR was significantly lower in obstructed kidneys than in unobstructed kidneys. 123Rhodamine, a marker for organic cation and P-glycoprotein transport, had a significantly lower maximum excretion rate in the obstructed than in unobstructed kidneys. Renal fractional clearance (123rhodamine clearance corrected for diminished GFR) was also significantly lower in obstructed kidneys. There was no significant difference in maximum excretion (absolute and corrected GFR) for Lucifer Yellow, a marker for sodium-dependent organic anion transport. The maximum excretion rate of calcein, a marker for sodium-independent organic anion transport, was significantly lower in the obstructed than in the unobstructed kidneys, but significantly higher after correcting for reduced GFR.

CONCLUSION

The IPK is a good model for studying the effect of neonatal renal obstruction on tubular drug transport. These results show that organic anion and cation transport mechanisms are affected differently by obstruction.

Reduced Tc-99m DMSA uptake in a patient with renal tubular acidosis: effect of acid-base imbalance

Tc-99m dimercaptosuccinic acid (DMSA) is used as a renal cortical imaging agent to detect parenchymal abnormalities especially in children. Kidney uptake of DMSA provides an index for evaluation of a functional tubular mass, which depends on the renal blood flow and proximal tubular cell membrane transport function. We here report a boy with renal tubular acidosis, which has noticeably reduced uptake on his Tc-99m DMSA scintigraphy, despite a totally normal Tc-99m MAG-3 study. The case reported here clearly demonstrates a situation in which renal uptake of DMSA may be dissociated from a functional renal mass and the importance of acid-base balance which alters Tc-99m DMSA uptake.

Quantitative and qualitative scintigraphic measurement of renal function in dogs exposed to toxic doses of Gentamicin

Five, 3-month-old mongrel dogs weighing between 4.5 to 5.5 kg were studied to evaluate and compare the efficiency of 99mTc-DTPA, 99mTc-MAG3, and 99mTc-DMSA in detecting gentamicin-induced renal tubular injury. After baseline renograms using all three methods, all dogs received daily intramuscular injections of gentamicin at a dose of 30-45 mg/kg. Additional studies were obtained after a cumulative dose of 450, 1,575, and 2,250 mg of gentamicin was reached. Glomerular filtration rate (GFR), effective renal plasma flow (ERPF), and percentage of total renal uptake measurements were calculated. Baseline and post-gentamicin injection blood urea nitrogen (BUN) and serum creatinine values were determined. A Duncan test revealed significant renal function impairment at 450 mgs of cumulated gentamicin with 99mTc-DMSA and at 1,575 mgs of cumulated gentamicin for 99mTc-DTPA and 99mTc-MAG3. There was no correlation between BUN and serum creatinine values when compared to gentamicin (p > 0.05). The images obtained with 99mTc-MAG3 were of better quality than those obtained with 99mTc-DTPA even under severe renal dysfunction. Percentage of 99mTc-DMSA uptake indicated renal damage, before than GFR and ERPF. BUN and serum creatinine measurements were poor indicators of gentamicin-induced renal failure.

Poor renal uptake of 99mtechnetium-dimercaptosuccinic acid and near-normal 99mtechnetium-mercaptoacetyltriglycine renogram in nephronophthisis

Four patients with the clinical diagnosis of nephronophthisis are presented, all having a very poor renal uptake of 99mtechnetium-dimercaptosuccinic acid (99mTc-DMSA) but clearly visualized kidneys on early images with 99mtechnetium-mercaptoacetyltriglycine and a normal or almost normal renogram. There was no difference between a young patient in an early stage of the disease and the other three patients with more advanced renal disease. In contrast, a patient with tubulointerstitial nephritis with uveitis had considerably better renal uptake of 99mTc-DMSA despite impaired renal function. We suggest that the specific tubular function defect in nephronophthisis might be the cause of the poor uptake of 99mTc-DMSA. We also recommend the method to support the clinical suspicion of nephronophthisis, even in the early stages of the disease.

Update on dimercaptosuccinic acid renal scanning in children with urinary tract infection

The dimercaptosuccinic acid (DMSA) renal scan is a method for assessing kidney function. Indications for DMSA scanning in children with urinary tract infection (UTI), as well as timing, have changed. Pitfalls in interpreting DMSA scans include: (1) acute pyelonephritis (APN), (2) tubular dysfunction, (3) hypertension, (4) use of captopril in patients with renovascular hypertension and (5) duplex kidneys. Interpretation of DMSA scans in children with UTI vary according to timing and clinical setting. During the course of a febrile UTI a DMSA scan may reveal a normal kidney, APN or a non-functioning, small and/or ectopic kidney. In the absence of UTI (up to 6 months) in children with vesicoureteric reflux a DMSA scan may indicate a normal kidney, renal scarring (reflux nephropathy), occult duplex kidney and allows the progression of scarring and hypertrophy of normal areas of the kidney to be followed anatomically. The DMSA renal scan in now the most reliable test for the diagnosis of APN. The transient abnormalities due to APN can occur in normal or scarred kidneys. Lesions due to reflux nephropathy (defined as a defect in the renal outline or contraction of the whole kidney) are permanent. Intravenous urography reveals renal abnormalities later than the DMSA scan. If abnormalities are seen on a DMSA scan performed during the course of APN it is impossible to predict the outcome: they can progress to permanent scarring or heal completely. An abnormal DMSA scan during a febrile UTI allows the identification of children at risk of developing renal scars. These children should be carefully investigated, maintained on long-term quimioprophylaxis and followed.

A comparative study of evaluating renal scars by 99mTc-DMSA planar and SPECT renal scans, intravenous urography, and ultrasonography

The purpose of this prospective study is to compare 3 types of 99mTc-DMSA renal scan [(a) planar, (b) x-ray type film static SPECT presentation (SPECT-1) and (c) dynamic three-view display of SPECT slices (SPECT-2)], intravenous urography, and ultrasonography in the diagnosis of renal scars. All these studies were performed in 130 pediatric patients, with urinary tract infection (42 patients), vesicoureteral reflux (37), and unilateral or bilateral small kidney(s) (51). The number of renal scars detected was highest with the 99mTc-DMSA renal SPECT-1 scan and next came the 99mTc-DMSA renal SPECT-2 studies. There is a significant difference (p < 0.05) between the ability of planar and SPECT-1 to recognize renal defects. However, SPECT-2 may provide the best stereotactic localization and image quality of all the methods.

A kinetic model for 99mTc-DMSA in the rat

A pharmacokinetic model was developed for the renal imaging agent 99mTc-DMSA in anesthetized rats, which incorporated data from serial measurements of blood and urine simultaneously with dynamic images obtained over an 8-h period. Animals which received a 10 mg/kg dose of unlabeled DMSA immediately before 99mTc-DMSA injection had a significantly reduced kidney accumulation and greater urinary elimination of 99mTc than animals which received the radiopharmaceutical alone. The kidney clearance was also significantly lower in rats receiving unlabeled DMSA, but no significant difference was determined between the urine clearance estimates of the two animal groups. Because the increase in the amount eliminated in the urine was not coupled with a significant change in urine clearance, it would appear that unlabeled DMSA saturated the kidney uptake mechanism(s) of 99mTc-DMSA without modifying the urinary clearance process. This interpretation is consistent with the hypothesis that renal handling of 99mTc-DMSA is governed by both glomerular filtration and peritubular capillary uptake. The simultaneous acquisition of blood, urine and non invasive image data allows for a comprehensive and informative model of the physiological disposition of 99mTc-DMSA.

Experimental obstructive hydronephrosis in newborn rats. XI. A one-year follow-up study of renal function and morphology

Partial obstruction of the left ureter was created in two-day-old rats and its effects on kidney function were studied with 99mTc-DMSA and 99mTc-DTPA after one, two, three and six weeks, and after one year. Kidneys from animals sacrificed at the age of six weeks or one year were also examined histologically. The obstructed renal pelvis was enlarged by about 35 times and there was a delayed excretion of 99mTc-DTPA during forced diuresis, indicating significant, chronic obstruction. The renal DMSA-uptake ratio (left kidney/(left and right kidney] was reduced to about 40% from the first week of obstruction. The parenchymal weight ratio (expressed as above) was reduced to about 45% after both six weeks and one year. The glomerular filtration rate, examined during forced diuresis and calculated on the basis of uptake capacity, was lowered to 42% after six weeks but was not significantly reduced after one year of obstruction. The incidence figures for medullary hemorrhage or accumulation of iron pigment, and chronic inflammatory changes in the cortex were somewhat higher after one year of obstruction than after 6 weeks, but the lesions were patchy in both groups. We conclude that partial unilateral ureteric obstruction, created in the neonatal period, leads to a slight but permanent functional disturbance and parenchymal weight reduction without prominent structural parenchymal damage.

Urography versus DMSA scan in children with vesicoureteric reflux

Following the diagnosis of primary vesicoureteric reflux, identified as part of the investigation of urinary tract infection, 299 refluxing kidneys in 202 children (aged 0-14 years) were prospectively evaluated using intravenous urography (IVU) and the DMSA renal scan at least 4 weeks after urine infection. There was 88% concordance between IVU and the DMSA scan, but in 12% there were discrepancies manifested in 37 kidneys from 31 children. Thirty-four kidneys were normal on IVU but showed scars of reflux nephropathy (RN) on the technetium 99m--dimercaptosuccinic acid (DMSA) renal scan; 4 of these (2 infants and 2 pre-school children) had severe generalized changes on scanning. Three kidneys were normal of DMSA scan and, although abnormal on initial IVU, were considered to be normal when this was repeated. During a follow-up period of 5 years an annual DMSA was undertaken in 194 patients and the renal scars remained unchanged in all except 1 child. The IVU was repeated 1-3 years after the initial study in 31 children in which the results of the first imaging did not agree. In 28 patients (34 kidneys) in which the initial IVU was normal but the DMSA abnormal, IVU evidence of scarring emerged in 30 of 34 kidneys, including the 4 patients with severe generalized damage on the DMSA. We conclude that abnormalities detected by the DMSA scan may precede the radiological findings, especially in young children. Even severe RN can be established in kidneys that appear normal on the IVU.

Two routes for 99mTc-DMSA uptake into the renal cortical tubular cell

Critical factors determining the renal handling of 99mTc-dimercaptosuccinic acid (DMSA) are protein binding in plasma and the renal 99mTc-DMSA extraction efficiency. Comparison of the count rate over soft tissue with that over the cardiac blood pool about 1 h after injection demonstrated that 99mTc-DMSA is not exclusively an intravascular label. 99mTc-DMSA was 76% protein bound in plasma as demonstrated by HPLC and gel filtration. Assuming that the 24% that is not protein bound is filtered at the glomerulus, the renal extraction efficiency of 99mTc-DMSA by glomerular filtration is about 5%. Since the total renal extraction efficiency was also found to be about 5%, the majority of the activity that becomes fixed in the renal cortex arrives there as a result of filtration followed by tubular reabsorption rather than by direct extraction from peritubular blood. However, discordant changes in DMSA and DTPA uptake induced by captopril in renovascular hypertension (RVH) suggested that a minority of uptake was by direct peritubular extraction. This kinetic model was supported by indirect measurement of protein binding and extraction efficiency based on the kinetics of 99mTc-DMSA disappearance from plasma and kinetics of uptake in the kidneys. Furthermore, differential functional studies based on 99mTc-DMSA and 99mTc-DTPA before and after captopril in patients with RVH due to unilateral renal artery stenosis confirmed filtration followed by tubular reabsorption as the predominant route for DMSA uptake by the kidney.

Imaging the kidneys and urinary tract in the neonate with acute renal failure

Transitional nephrology seriously affects the manner in which radiological investigations and other forms of imaging are undertaken in the neonate. When this is complicated by acute renal failure then caution must be exerted in taking care of the neonate. The use of ultrasound and micturating cystourethrography are well described and form the baseline for all imaging of the renal tract. The physiological handling of TC99m DTPA and the contrasts used for IVU are described as well as the normal appearances of these techniques in the neonate. TC99m DMSA is also included, as are other modalities of imaging.