Page 339 - Libro 2

20 — The Renal Vasculature
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imaging facilitate recognition of regions of flow disturbance, stenosis, occlusion, and anatomic anomalies. Visualization of the blood flow vectors eases placement of the Doppler sample volume for waveform analysis and measurement of velocities. The determination of disease severity is based on the PSV and the presence or absence of a poststenotic signal in the main renal artery. The assessment of velocity waveform parameters recorded within the renal parenchyma yields clues to the presence of intrinsic renal disease and the likelihood of successful revascularization. The role of indirect renal hilar duplex for the identification of flow-limiting renal artery disease remains controversial. At present, studies have shown that it is best used to complement direct and complete examination of the renal arteries and kidneys. Given the broad scope of diagnostic information that can be obtained using ultrasound to interrogate the renal vasculature, it is not surprising that duplex sonography is recognized as the ideal technology for the identification of renal vascular disease and for follow-up after endovascular or surgical intervention. The technical success of each study is influenced by the experience of the examiner and the physician interpreter. Complete and accurate examinations of the renal vasculature are possible in more than 90% of patients when the study is performed in high volume laboratories by experienced, credentialed sonographers and interpreted by qualified physicians, both of whom have a knowledge of renal vascular disease, the validated techniques used for assessment of the renal vasculature, and the current diagnostic criteria used for the classification of renal artery stenosis.
Critical Thinking Questions
1. A patient presents for a renal duplex scan. Prior to initiating the examination, you can determine the approximate location of this patient’s renal arteries
by noting several body surface landmarks. What are the most important landmarks to use to accomplish this goal?
2. During the renal sonographic examination, there are other important anatomic landmarks to use for locating the renal arteries. Which of the landmarks are most commonly used?
3. It is always important to consider the patient’s clinical presentation. If a 40-year-old hypertensive female presents for renal duplex examination, what would be the most likely pathology responsible for her renovascular hypertension?
4. A patient of large body habitus presents for a renal duplex examination. With the patient lying supine, you are able to image the abdominal aorta in both sag- ittal and cross-sectional planes but you cannot visualize the right renal artery. What steps can you take to determine if the renal artery is patent or occluded?
5. A PSV of 220 cm/s is recorded in the proximal segment of a tortuous right renal artery. How would you determine whether the elevated velocity was the result of flow-limiting stenosis or vessel angulation?
REFERENCES
1. Berglund G, Anderson O, Wilhelmensen L. Prevalence of primary and secondary hyperten- sion: studies in a random population sample. Br Med J. 1976;2(6035):554–556.
2. Dunnick NR, Sfakianakis GN. Screening for renovascular hypertension. Radiol Clin North Am. 1991;29:497–510.