SONOGRAPHIC AND SCINTIGRAPHIC EVALUATION OF ACUTE RENAL ALLOGRAFT REJECTION IN CATS

Evaluating feline lower urinary tract disease: Doppler ultrasound of the kidneys

OBJECTIVES

Ultrasonography is used in the evaluation of urinary disorders, and the resistivity index (RI) and pulsatility index (PI) have been successfully used to detect early hemodynamic changes in the course of kidney diseases in humans and dogs. The aim of this study was to investigate RI and PI in cats with feline lower urinary tract disease (FLUTD).

METHODS

Twenty-nine client-owned cats were selected and divided into a control group (CG; n = 10), a group of animals with obstructive FLUTD (OG; n = 11) and non-obstructive FLUTD (nOG; n = 8). Clinical, laboratory and ultrasound evaluations were performed in all cats.

RESULTS

RI and PI values for cats in the CG were below the upper limit of normal suggested in other studies, while cats with FLUTD showed significantly higher values in the assessment of RI (P = 0.027 and P = 0.034, respectively) and PI (P = 0.044 and P = 0.048, respectively) of the right and left kidneys.

CONCLUSIONS AND RELEVANCE

Alteration in renal blood flow was observed in cats with lower urinary tract disorders, even in the nOG group. To the best of our knowledge, this is the first report of renal blood flow changes related to non-obstructive FLUTD.

Resistivity and pulsatility indexes in feline kidney disease: a systematic review

Doppler ultrasonography is used in the evaluation of hemodynamics, and the resistivity (RI) and pulsatility (PI) indexes provide information about resistance to blood flow within a vessel. This systematic review was carried out to evaluate renal RI and PI in clinically healthy and nonsedated cats and as well as their usefulness in the evaluation of kidney disease in cats. An electronic search in the PubMed, Scopus, and Web of Science databases was carried out using the terms "resistive index" or "resistivity index" or "pulsatility index;" "Doppler;" "renal" or "kidney;" and "cat" or "feline" in titles, abstracts, and keywords. Variables of interest related to experimental model features, research methods, and technical resources were extracted from the studies. The methodological quality was assessed with SYRCLE's risk of bias tool. Thus, 14 studies involving healthy and sick cats were selected. Interestingly, the upper limits estimated for both RI and PI varied among studies. The upper limits of renal RI for healthy cats varied between 0.64 and 0.72, while for PI, the values varied from 1.06 to 1.29. A limited number of studies evaluated cats with kidney disease. In most studies, RI values of kidneys with different conditions were significantly different from kidneys of healthy animals, indicating that RI values increase with kidney disease. The parameters body weight, heart rate, and age seem to influence the RI values. Standardized studies regarding its realization and description are still necessary to define normal values and analyze its applicability in the clinical diagnostic routine.

Quantification of renal T2 relaxation rate by use of blood oxygen level-dependent magnetic resonance imaging before and after furosemide administration in healthy Beagles

OBJECTIVE

To assess the feasibility of blood oxygen level-dependent (BOLD) MRI for measurement of the renal T2^* relaxation rate (R2^*; proxy for renal oxygenation) before and after furosemide administration and to evaluate the reliability and repeatability of those measurements in healthy dogs.

ANIMALS

8 healthy adult Beagles (4 males and 4 females).

PROCEDURES

Each dog was anesthetized and underwent BOLD MRI before (baseline) and 3 minutes after administration of furosemide (1 mg/kg, IV) twice, with a 1-week interval between scanning sessions. Mapping software was used to process MRI images and measure R2^* and the difference in R2^* (ΔR2^*) before and after furosemide administration. The intraclass correlation coefficient was calculated to assess measurement reliability, and the coefficient of variation and Bland-Altman method were used to assess measurement repeatability.

RESULTS

Mean ± SD baseline R2^* in the renal medulla (24.5 ± 3.8 seconds^-1) was significantly greater than that in the renal cortex (20.6 ± 2.7 seconds^-1). Mean R2^* in the renal cortex (18.6 ± 2.6 seconds^-1) and medulla (17.8 ± 1.5 seconds^-1) decreased significantly after furosemide administration. Mean ΔR2^* in the medulla (6.7 ± 2.4 seconds^-1) was significantly greater than that in the renal cortex (2.1 ± 0.7 seconds^-1). All R2^* and ΔR2^* values had good or excellent reliability and repeatability, except the cortical ΔR2^*, which had poor repeatability.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that BOLD MRI, when performed before and after furosemide administration, was noninvasive and highly reliable and repeatable for dynamic evaluation of renal oxygenation in healthy dogs.

Evaluation of a microvascular anastomotic coupler for end-to-side arterial and venous anastomosis for feline renal transplantation

OBJECTIVE

To describe the technique and determine the feasibility of an end-to-side (ETS) anastomosis of the renal vein to vena cava and renal artery to aorta using a microvascular anastomotic coupler (MAC) for feline renal transplantation.

STUDY DESIGN

In vivo experimental study.

ANIMALS

Six purpose-bred domestic shorthair cats.

METHODS

The left kidney was autotransplanted using a MAC for ETS vascular anastomosis. Outcomes included intraoperative hemorrhage from the anastomosis sites, duration of anastomoses, surgical complications, postoperative renal perfusion (including resistive index (RI)) measured by Doppler ultrasonography and computed tomography angiography, and histopathological examination of the left kidney and anastomosis sites (30 days).

RESULTS

Anastomosis was successful in all cats, and intraoperative hemorrhage was negligible. Intraoperative renal perfusion was considered excellent. Venous and arterial anastomoses were completed in 11 minutes 20 seconds (range, 6:38-13:27) and 21 minutes 50 seconds (range, 11:05-30:24), respectively. Vascular occlusion time was 32 minutes (17:43-42:03). One cat was euthanized 5 hours postoperatively because of bleeding from a muscular arterial branch of the dorsal aorta causing hemoabdomen. Renal perfusion and RI of the remaining five cats were within normal range (<0.8) and similar to the contralateral kidney at all time points. Endothelialization of the anastomosis was complete with mild-to-moderate fibrosis surrounding the MAC in all cats.

CONCLUSION

End-to-side anastomosis of the renal vein and artery to the vena cava and aorta, respectively, was consistently achieved in all six cats with the MAC.

CLINICAL SIGNIFICANCE

The use of the MAC may be considered as an alternative to hand suturing for ETS anastomoses for feline renal transplantation.

Doppler evaluation of renal resistivity index in healthy conscious horses and donkeys

The renal resistive index (RRI) is used as a measurement of downstream resistance in arteries. The aim of this study was to assess the RRI of the arcuate arteries by pulsed-wave Doppler ultrasonography in healthy conscious horses and donkeys, and to verify any differences related to age, breed, bodyweight (BW) or body condition (BCS). Thirty-three healthy conscious horses and nine donkeys had their systolic and diastolic flow velocities at the level of the arcuate arteries estimated by pulsed-wave Doppler ultrasound, and the RRI was calculated. The relationship of RRI with age, breed (Trotters vs. other breeds), bodyweight (BW), and body condition score (BCS) were evaluated. PW Doppler evaluation of RRI was successfully applied in most of the horses, but to date not in the donkeys. In horses, median RRI values for the right kidney (0.58±0.006) were statistically higher than for the left (0.51±0.006). For the donkeys the values were comparable. There was no significant difference in RRI between horses younger or older than 15 years, and between breeds in horses. No correlation with age, BW or BCS was found in either horses or donkeys.

Resistive index for kidney evaluation in normal and diseased cats

OBJECTIVES

The objectives were to determine the resistive index (RI) in normal cats and in cats with various renal diseases, and to evaluate the effect of age on RI.

METHODS

The subjects were cats that had ultrasonography (US) of the urinary tract and RI measurement at our centre between January 2003 and April 2014. Based on clinical evaluation, biochemical and haematological tests, urinalysis and US, the cats were classified as healthy or diseased. RI measurements were made from the interlobar or arcuate arteries. Data were analysed for differences between the right and the left kidney, the two sexes, different age groups in healthy cats, and between healthy and diseased cats.

RESULTS

A total of 116 cats (68 males, 48 females) were included: 24 healthy and 92 diseased. In the healthy cats, RI (mean ± SD) differed significantly (P = 0.02) between the right kidney (0.54 ± 0.07) and the left kidney (0.59 ± 0.08). For the left kidney, RI was significantly higher in cats with chronic kidney disease (0.73 ± 0.12) and acute kidney injury (0.72 ± 0.08) (P = 0.0008). For the right kidney, RI was significantly higher in cats with chronic kidney disease (0.72 ± 0.11), acute kidney injury (0.74 ± 0.08), polycystic kidney disease (0.77 ± 0.11) and renal tumour (0.74 ± 0.001) (P <0.0001). There was no significant effect on RI value in either kidney in terms of age or sex.

CONCLUSIONS AND RELEVANCE

RI could be considered a valuable diagnostic tool in cats, useful in the differential diagnosis of diffuse renal diseases. While it does not change with the age of the cat, ultrasonographers should be aware that RI may differ between the two kidneys.

Clinical approach to advanced renal function testing in dogs and cats

Serum creatinine concentration is insensitive for detecting kidney injury and does not assist in differentiation between glomerular versus tubular damage. Advanced renal function tests, including glomerular filtration rate testing, determining fractional excretion of electrolytes, and assay of urine biomarkers, may allow earlier detection of reduced renal function mass, differentiation of renal from non-renal causes of azotemia, and assist with localization of damage. This article reviews the principles, indications, and limitations of these tests and describes their use in sample clinical scenarios.

An overview of glomerular filtration rate testing in dogs and cats

Determination of glomerular filtration rate (GFR) is a valuable, yet underused, diagnostic tool for evaluating renal function in dogs and cats. This article first reviews the hormonal and hemodynamic factors which contribute to GFR, followed by a description of considerations when selecting a pharmacokinetic model and methods of animal-to-animal standardization. The best-characterized existing GFR markers, including creatinine, radiolabeled markers, and iohexol, are reviewed in depth, as well as alternative but lesser used techniques. A weighted means analysis of reported GFR measurements in healthy dogs and cats and a review of selected studies that have examined GFR alterations in animals with naturally occurring and experimental diseases provide the reader with preliminary guidelines on expected GFR results in these species and disease conditions.

Contrast-enhanced ultrasound of the feline kidney

Contrast-enhanced ultrasound offers a noninvasive means of subjectively and quantitatively evaluating renal perfusion in cats with renal disease, or in renal transplant patients. In this study, we characterized the pattern of ultrasonographic contrast enhancement in 16 normal feline kidneys in eight cats using contrast-enhanced power Doppler and contrast-enhanced harmonic ultrasound techniques. Mean time to peak contrast enhancement for the whole kidney was longer using contrast-enhanced harmonic ultrasound (16.8s, SD 4.7s) than contrast-enhanced power Doppler ultrasound (12.2s, SD 1.8s). The time to peak enhancement for the cortex alone in contrast-enhanced harmonic ultrasound was 13s (SD 3.2s), and for the renal medulla was 25.5s (SD 8.7s). The half time for washout of contrast agent was 39s (SD 14.5s) for contrast-enhanced harmonic ultrasound. The pattern of contrast enhancement in these normal feline kidneys can be used as normal reference values for the evaluation of clinical patients. Contrast-enhanced harmonic ultrasound may allow the differentiation between cortical and medullary perfusion patterns.

Indicators of Acute Rejection on Tc-99m DTPA Renal Scintigraphy

INTRODUCTION

Specific criteria for diagnosing an acute rejection episode (ARE) are not present on renal scintigraphy. However, a deterioration in renal function observed on serial imaging is suggestive of an ARE during the early posttransplantation period. In this study, we evaluated Tc-99m DTPA renal scintigraphy findings among patients with renal allograft dysfunction. The aim was to define criteria for ARE on a single imaging study alone.

MATERIALS AND METHODS

This study included 82 patients with renal allograft dysfunction, each of whom had a specific biopsy-proven pathology. From the background-corrected Tc-99m DTPA renal time-activity curves, the following parameters were computed: the ratio of counts at peak perfusion to that at plateau (P:PL) and the ratio of counts at peak perfusion to that at peak uptake (P:U). The images were inspected visually for excretion patterns and other morphological changes.

RESULTS

A specific renogram pattern, that is an increase in perfusion to uptake ratio together with a nearly flat uptake curve and preserved peak/plateau pattern, was observed in 67% of low-grade AREs. In contrast, a flat uptake curve usually occurred together with a loss of peak/plateau pattern in a high-grade ARE. The findings that were highly specific for ARE on visual inspection were little or no collecting system activity, pelvic hypoactivity, and indistinctness of the corticomedullary junction.

CONCLUSIONS

Our results indicate that in low-grade ARE, there is decreased filtration relative to perfusion as evidenced by a decrease in the perfusion-to-uptake ratio with loss of a peak/plateau pattern. A hypoactive pelvis with little activity in the collecting systems may be due to edema in the renal interstitium and pelvicalyceal structures.

Glomerular filtration rate and renal scintigraphy

Clinical evaluation of early renal dysfunction is problematic in the nonazotemic animal. Measurement of glomerular filtration rate (GFR) provides the most accurate assessment of renal function. However, many methods of determining GFR are not practical for use in routine veterinary practice. This article provides a description and literature review of methods to determine GFR, including benefits and drawbacks of each method for the practicing veterinarian.