ARFI of NORMAL KIDNEY and HYDRONEPHROSIS in CHILDREN

Discussion

Hydronephrosis is an obstructive or non-obstructive nephropathy that is a commonly identified disease during pediatric abdominal ultrasonography. Congenital obstructive nephropathy constitutes the single most important identifiable cause of renal impairment in infants and children [10-12]. In obstructive nephropathy, interstitial fibrosis eventually develops and leads to a loss of nephrons [10].

Numerous papers that focus on the molecular biological mechanisms associated with renal interstitial fibrosis due to obstructive nephropathy have been recently published [10,13,14]. However, there is limited radiological research on renal interstitial fibrosis in the case of hydronephrosis. This could be attributed to the difficulty of detection, evaluation, and quantification of interstitial fibrosis by radiological methods.

There are many studies that explored ARFI measurements as a means of evaluating tissue stiffness, including several studies on kidneys. Gallotti et al. [6], Eiler et al. [7], and Goertz et al. [8] measured the ARFI velocities of normal kidneys in healthy adults.

Further, there have been several trials using ARFI in adult kidneys to evaluate renal masses, to assess renal allograft fibrosis, and to detect chronic kidney diseases [15-17]. However, there is a lack of studies involving ARFI measurements in young children. This could be attributed to the fact that the previously used low-frequency transducer is not effective in the case of such small patients.

However, the availability of the 4-9-MHz high-frequency linear transducer makes it possible to measure SWVs in small subjects. Recently, our group demonstrated normal values of SWVs using ARFI in pediatric abdominal organs including kidneys in 202 children with an average age of 8.1±4.7 years [1]. The mean SWVs were 2.19 m/sec for the right kidney and 2.33 m/sec for the left kidney in the above mentioned study. The previously reported mean SWVs in normal adult kidneys were 2.24-2.37 m/sec, with no significant difference between the right and the left kidney [6,8]. The median SWVs in normal kidneys in the present study were 1.75 m/sec without any difference between the right and the left ones. This value is relatively low as compared to that obtained in previous studies. However, this result is comparable with that of our previous study, which concluded that the mean ARFI SWV for the kidneys increased according to age in children less than 5 years of age [1].

In this study, we only included children under the age of 24 months. Only one study has been performed on the evaluation of diseased kidneys in children. Bruno et al. [5] conducted a study of ARFI measurements in pediatric patients with vesicoureteral reflux. The study suggested that ARFI can provide reliable information about the severity of renal damage and maybe useful in the diagnostic workup in children with a chronic reflux renal disease. However, the patient age in the study ranged from 8 to 16 years. Therefore, our study is the first report evaluating ARFI for hydronephrotic kidneys in young children.

We aimed to correlate SWVs with the hydronephrosis grade. Even though there are hydronephrosis grading systems on ultrasonography [11,18,19], these could not definitely differentiate between obstructive and non-obstructive hydronephrosis. Further, these systems cannot suggest the grade of renal parenchymal fibrosis. If SWVs have a correlation with the renal parenchymal stiffness, its measurement would be helpful in evaluating the status of a patient’s kidney. Further, SWV can show a continuous spectrum of stiffness.

On the other hand, the grading system has an ordinal scale that cannot show a continuous value. Therefore, elastography has a possibility of having an additional value to evaluate hydronephrosis. In our study, there was a significant difference in the median SWVs between normal kidneys (1.75 m/sec) and high-grade hydronephrotic kidneys (2.02 m/sec). This suggests that elasticity decreases and stiffness increases in high-grade hydronephrotic kidneys. However, ARFI measurements cannot differentiate the cause of stiffness change such as tissue fibrosis and edema. Further research with a large group of patients and pathologic correlation is needed.
We also compared SWVs for a hydronephrotic kidney with and without UPJO. Further, there were only seven patients proven to have UPJO during the study period. The mean ARFI velocities were 0.69-2.51 m/sec for hydronephrotic kidneys without UPJO and 1.54-2.72 m/sec for those with UPJO; there was no statistical difference. Kidneys with VUR and a parenchymal scar change also exhibited no remarkable difference in SWVs. This could be attributed to the small number of patients, variable interstitial fibrosis of the UPJO group, and heterogeneous parenchymal scar change in the refluxing kidneys. This needs further evaluation with a large number of patients.

This study has several limitations. Almost all previous studies performed in adults measured about 5-10 valid SWVs and used mean values. However, due to the characteristics of the pediatric patient group, only three valid SWVs were obtained in this study.

Repetitive measurements over a long time while subjects hold their breath is not possible in many children, particularly young children. Although only three valid ARFI velocities were attempted, two children could not tolerate the examinations and the success rate was 96%. Moreover, subjects were allowed to breathe freely during measurements. Thiscan increase the variability of SWV. The development of a method to measure SWV without breathholding would lead to more reliable results. 

The second limitation is the representativeness of the ARFI value.To represent a global kidney, measurement should be performed on multiple sites of the kidney, such as the upper, mid-, and lower poles. However, if the upper and lower poles are to be imaged, it is necessary to use a similar angle of incidence in all patients relative to the tubular system to avoid anisotropy issues. It is conceivable that shear waves generated within the kidney move at different velocities depending on the angle of incidence [20]. We tried to measure SWVs at the same portion of the mid-pole from the axial view, as parallel to the tubular system as possible in order to reduce the angle effect. The variation of the depth of the ROI position should also be considered.

We targeted renal parenchyma, including both the renal cortex and the medulla, from the axial view in each patient. Therefore, we might expect that the depth of the ROI position would be different between patients and could increase according to the body size. Further study is needed to evaluate the effect of the depth of the ROI position and the body size in children. 

The fourth limitation is that we considered the contralateral kidneys without hydronephrosis as normal in the hydronephrosis group. Even though we demonstrated no significant difference in SWVs between normal kidneys in the normal group and contralateral kidneys in the hydronephrosis group, there could have been a physiological change in the bilateral kidneys of the hydronephrosis group.

In conclusion, obtaining ARFI measurements of kidneys using a high-frequency transducer is feasible in very young pediatric patients. The median SWV of normal kidneys in children under the age of 24 months was 1.75 m/sec. These velocities increased in high-grade hydronephrotic kidneys but were not helpful in differentiating hydronephrotic kidneys with and without UPJO.

Beomseok Sohn; Myung-Joon Kim; Sang Won Han; Young Jae Im; Mi-Jung Lee.

AT MEDIC CENTER:

We applied ARFI technique from Siemens S2000 to evaluate whether fibrotic process existing in adult hydronephrosis.
Using 1-4 MHz convex probe we calculated in 3 positions of hydronephotic kidney due to  obstruction [stone, outside compression] (n=27 cases), due to ureteropelvic junction obstruction [UPJO] (n=30 cases]. We had a control group of normal kidney (n=36 cases).

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Experience Matters in point-of-care Ultrasound of Appendicitis

Experience matters in point-of-care ultrasound

By Erik L. Ridley, AuntMinnie staff writer

May 19, 2014 -- Experienced sonologists had significantly higher sensitivity for diagnosing appendicitis with point-of-care ultrasound than sonologists with less experience, in a study from Mount Sinai School of Medicine. Either way, though, it's important not to rely only on point-of-care ultrasound to rule out the condition.

 In the prospective study of 150 patients, experienced sonologists' sensitivity was nearly 30% higher than that of their less experienced colleagues.

"To minimize the possibility of errors, sonologists should avoid ruling out appendicitis based on [point-of-care ultrasound] results alone," said Dr. James Tsung from the department of emergency medicine. "So you need the clinical picture, and if there's uncertainty, certainly proceed with radiology imaging."

He presented the research during a scientific session at the recent American Institute of Ultrasound in Medicine (AIUM) annual meeting.

The experience effect

While it's well-known that ultrasound is an operator-dependent imaging modality, the effect of operator experience on point-of-care ultrasound hasn't yet been studied, according to Tsung.

In medicine, misdiagnosis-related errors are much more common than medication errors and can lead to poor patient outcomes. These types of errors can be minimized, however, by understanding the relationship between operator experience and a test's performance characteristics, he said.

With that in mind, the Mount Sinai team sought to evaluate the effect of operator experience on the sensitivity and specificity of point-of-care ultrasound in a prospective study of 150 children.

For inclusion in the study, patients had to be 21 years or younger, have abdominal pain with nausea and/or vomiting, and require imaging or laboratory evaluation for suspected appendicitis. Patients were excluded if they required immediate resuscitation, had prior imaging for suspected appendicitis, or had known inflammatory bowel disease.

Point-of-care ultrasound exams were considered positive for appendicitis based on standard sonographic definitions for appendicitis, while negative results included a normal appendix finding and also nondiagnostic studies. For the purposes of the study, the gold standards were operating-room/pathology reports for patients who required surgical operations, and a three-week phone follow-up for nonoperative patients.

Experienced sonologists enrolled more than 25 patients in the study and had diagnosed appendicitis using point-of-care ultrasound prior to the study test, while novice sonologists enrolled fewer than 25 patients and hadn't diagnosed appendicitis yet using point-of-care ultrasound.

The researchers then stratified the test performance characteristics by novice versus experienced sonologists, analyzing the relationship between operator experience, prevalence of appendicitis, and the rate of nondiagnostic scans.

Of the 150 patients who received point-of-care ultrasound, 61 (40.6%) exams were performed by an experienced sonologist and 89 (59.3%) were performed by a novice. Patients went on to receive either follow-up radiology ultrasound or CT; those with positive imaging findings went on to the operating room, while the rest were admitted or discharged.

There was an overall appendicitis prevalence rate of 33.3% in the study, which is in line with prior literature for ultrasound and appendicitis. No missed cases were discovered at the three-week phone follow-up, and there were no negative laparotomies in the operative patients.

Higher sensitivity

The 61 studies performed by the experienced sonologists included 48 negative and 13 positive exams, while the 89 studies handled by the novice sonologists included 67 negative and 22 positive exams.

Sensitivity and specificity of point-of-care ultrasound
	Sensitivity	Specificity
Overall point-of-care ultrasound (150 patients)	60%	94%
Experienced sonologists (63 patients)	80%	98%
Novice sonologists (89 patients)	51.4%	93%
Radiology ultrasound (117 patients)	62.5%	99.3%

The overall sensitivity and specificity for point-of-care ultrasound is in line with the literature, Tsung said.

"If you look at the spread between sensitivity [for experienced and novice sonologists], you've got like a 28 [percentage point] spread, whereas the spread between novice and experienced in specificity is much smaller, about five [points]" he said. "If you look at radiology ultrasound, they had a relatively low sensitivity relative to what's in the literature, but their specificity was excellent."

Tsung noted that point-of-care ultrasound preceded the radiology ultrasound study, an order that will naturally bump up the specificity of the radiology ultrasound study. In addition, radiology residents performed radiology ultrasound at their institution, which is why sensitivity was lower than would be expected.

"A lot of the residents just weren't comfortable with the scan," he said.

Additional point-of-care ultrasound results
	Nondiagnostic studies	Appendicitis prevalence
Overall point-of-care ultrasound	69%	33.3%
Experienced sonologists	67%	24.6%
Novice sonologists	71%	39.3%
Radiology ultrasound	59%	37.6%

"What [the appendicitis prevalence numbers] suggest is that the patients the novices tended to enroll [in the study] probably had more apparent appendicitis," he said.

Based on the differences between the two sonologist groups, the researchers concluded that operator experience had a greater effect on sensitivity to rule out appendicitis compared with specificity.

"Our ability to rule out pathology is more operator-dependent than specificity," he said.

Tsung acknowledged a number of limitations to the research; for example, it was a single-center study, relied on a convenience sample, and utilized a small sample size for subgroup analysis, he said.