Ultrasonographic Tissue Characterization of Kidneys in Patients with Unilateral Renal Artery Stenosis

Abstract

Introduction

Ultrasound tissue characterization (USTC) has been applied to B-mode images of normal, young and transplanted kidneys, carotid, and peripheral atherosclerosis and venous thrombosis. We analyzed USTC from both kidneys of patients with severe unilateral renal artery stenosis. Seven women and 11 men, 79 ± 9 standard deviation (range = 57–96) years of age, were included. Severe, unilateral, renal artery stenosis was based on renal artery peak-systolic velocity (PSV) > 200 cm/sec and/or renal-aortic PSV ratio > 3.5. This sample population, selected sequentially by date of ultrasonographic examinations requested, was heterogeneous: kidney lengths and resistivity indices varied from 6.7 to 13.4 cm and 0.45 to 0.85.

Methods

USTC was applied to images selected for kidney length measurements. Pixel brightness in the 0–255 range was rescaled to zero for black and 200 for fascia brightness. Gray-scale medians (GSM) of entire kidneys were estimated for statistical comparisons between: (a) kidneys ipsilateral to stenosis (KIS), (b) kidneys contralateral to stenosis (KCS), and (c) normal, young kidneys (KN), previously published GSM = 37 ± 6 (27–48).

Results

Two distinct KCS subgroups were identified: (1) near-normal GSM < 54 (KCSN, n = 10, 56%); and (2) elevated GSM > 60 (KCSH, n = 8, 44%). Subgroup increasing GSM order was (1) KN, (2) KCSN (47 ± 7, > KN, p < 0.002), (3) KIS-CN (59 ± 20, >KCSN, p < 0.003), (4) KIS-CH (73 ± 20, > KCSN, p < 0.007), and (5) KCSH (78 ± 17, >KIS-CN, p < 0.05). GSM was independent of kidney length or resistivity index, with Pearson correlation coefficients < 0.5 for either KIS or KCS, respectively.

Conclusions

Tissue echogenicity, represented by GSM, was an independent variable characterizing effects of unilateral renal artery stenosis on the ipsilateral or on both kidneys.