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PART 5 — ABDOMINAL
The true prevalence of renovascular hypertension is unknown but is estimated to affect approximately 50 million people in the United States alone.1,2 As many as 6% of hypertensive patients have underlying renal disease as the cause of their ele- vated blood pressure.2,3 In patients with severe dia- stolic hypertension, the prevalence of renal artery stenosis approaches 40%. Progression of stenosis occurs in 31% to 49% of patients depending on the initial severity renal artery narrowing.3–5 Renal artery stenosis should be suspected in adults with sudden onset or worsening of chronic hypertension; azo- temia, which is induced by angiotensin-converting enzyme inhibitor; unexplained renal insufficiency or pulmonary edema; and in hypertensive children.6 In the majority of patients, renal artery disease is cor- rectable with treatment providing control or cure for renovascular hypertension, retention of renal mass, and stabilization of renal function in patients with chronic renal failure.7
For identification of renovascular disease, contrast arteriography has historically been the procedure of choice. Although it provides anatomic information, this diagnostic test does not identify the functional significance of renal artery disease in hypertensive patients, nor does it provide hemodynamic informa- tion. Because of its associated, albeit low, morbidity, this invasive test is most often reserved for defining therapeutic intervention. Magnetic resonance angi- ography (MRA) and computed tomography angiog- raphy (CTA) offer less invasive diagnostic testing and excellent sensitivity and specificity, but are relatively expensive and require the injection of intravenous
contrast.8 It should be noted that in the case of CTA, the contrast agent may be nephrotoxic and is, there- fore, unsuitable for use in patients with renal insuf- ficiency. Given these deficiencies, many clinicians reserve MRA and CTA for use as secondary con- firmatory studies and have focused their attention on duplex sonography as a primary diagnostic tool. Sonographic imaging can be performed on an out- patient basis at low cost without the risk of ionizing radiation or the use of nephrotoxic contrast agents. This modality has the additional advantages of being noninvasive and painless and has demonstrated an overall accuracy of 80% to 90% for identification of renal artery stenosis and definition of its hemody- namic significance.9
ANATOMY
The kidneys are located retroperitoneally in the dorsal abdominal cavity between the 12th thoracic and the 3rd lumbar vertebrae with the right kidney usually lying more inferior to the left (Fig. 20-1). The normal organ length is 8 to 13 cm with a width of 5 to 7 cm. The kidneys decrease in size with increasing age. An uncommon finding is a horseshoe kidney, which occurs in less than 1% of the population. In an excess of 90% of cases of horseshoe kidney, the organs are joined at their lower poles by an isthmus of tissue, which lies anterior to the aorta at the level of the fourth or fifth lumbar vertebrae.
For the purpose of sonographic interrogation, the kidneys are segmented into four main areas
Inferior vena cava
Adrenal gland
Right kidney
Left kidney
Renal artery
Renal vein Renal pelvis
Abdominal aorta
Ureter
Figure 20-1 Diagram illustrating the anatomic location of the kidneys.