Diagnostic ultrasound ( PDFDrive )

CHAPTER 12 The Retroperitoneum 447
Feasibility of the examination in obese patients is also a
concern. A few years ater starting our duplex Doppler sonography
program, we studied a total of 100 consecutive main renal arteries
(50 patients), recording the body mass index (BMI) of each
patient (unpublished data, 2002, Saint Francis Medical Center,
Peoria, Ill). Of the 100 arteries, 20 were in obese patients (BMI
≥ 30) and 4 in extremely obese patients (BMI ≥ 40), 30 arteries
were in overweight patients (BMI ≥ 25), and 46 were in patients
of normal weight. We were able to complete a technically adequate
examination in 96 of the 100 arteries. Of the 4 arteries with
failed studies, 3 were in overweight patients, and 1 was in a
patient of normal weight. All 24 arteries of the obese or morbidly
obese patients were successfully studied.
Our technologists routinely score the quality of the duplex
sonography of each renal artery on a 5-point scale. All examinations
graded 2 or higher are considered diagnostically adequate;
the entire extrarenal portion of the artery has been successfully
interrogated. Our mean Duplex quality score was from 4 to 4.6
in all the categories. Our experience shows that renal duplex
Doppler sonography can be completed successfully in most obese
patients.
Causes of Renal Artery Stenosis. he most common
causes of renal artery stenosis in adults are atherosclerosis and
ibromuscular dysplasia. 77 Atherosclerotic disease most oten
occurs in the proximal third of the artery, oten at the origin of
the artery. 77 Percutaneous transluminal angioplasty alone has
had mixed results in the treatment of atherosclerotic disease. In
lesions that are at the origin of the artery, there tends to be strong
elastic recoil that allows the balloon to be inlated fully but causes
the artery to revert quickly to its stenotic state on delation of
the balloon. he development of stents has changed the situation
by allowing the artery to be scafolded. Ater stenting, there
remains a risk of restenosis secondary to neointimal hyperplasia.
74,79 Restenosis is seen in 10% to 20% of patients between 6
and 12 months ater stenting 80,81 and is yet higher for patients
followed for longer than 1 year (Videos 12.6, 12.7, and 12.8).
Because of the relatively low cost, lack of iodinated contrast, and
high accuracy, renal artery duplex Doppler sonography is an
ideal method to use when following stented arteries.
Fibromuscular dysplasia (FMD) is the second most common
cause of renovascular hypertension and typically occurs in women
aged 20 to 50 years. Multiple pathologic subtypes are seen; the
most common FMD in the renal arteries is medial ibroplasia. 82,83
FMD lesions most oten occur in the distal two-thirds of the
renal artery and oten have an angiographic appearance suggestive
of a thin, ibrous web. he classic appearance on angiography is
the “string of pearls,” caused by multiple dysplastic regions in a
row with short areas of poststenotic dilation immediately distal
to each stenosis (Fig. 12.18). FMD oten responds well to simple
percutaneous transluminal angioplasty. A single treatment oten
is efective in controlling blood pressure and is enduring. 84 Stent
placement is rarely needed for FMD.
Another cause of impaired blood low to the kidney that may
result in renovascular hypertension is dissection. If the dissection
extends to the renal artery, the raised intimal lap in the aorta
may partially or completely occlude the renal artery oriice.
Alternatively, if the dissection extends into the renal artery, the
FIG. 12.18 Fibromuscular Dysplasia: Angiography. Note the “string
of beads” appearance, most often in the distal two-thirds of the renal
artery.
raised intima may cause stenosis or occlusion within the artery
itself. Endovascular treatment is frequently successful either by
stenting of the narrowed artery or by fenestration of the dissected
intima 85 (Fig. 12.19).
Embolus can result in abruptly impaired blood low to some
or all of a kidney. he patient frequently complains of lank pain.
Diagnosis oten is delayed, resulting in irreversible damage
to the kidney involved. he kidney can tolerate only a brief
episode of warm ischemia. 86 Revascularization of the kidney is
unlikely to result in full return of function if it is delayed more
than 90 minutes. 87
Vasculitis is an uncommon cause of renal artery stenosis in
adults. he vasculitides that are most likely to cause stenosis of
large vessels are Takayasu arteritis and giant cell arteritis. 88
Renal artery stenosis can also occur in children; FMD is the
most common cause. Neuroibromatosis and vasculitis can also
cause renal artery stenosis in children. 89 Midaortic syndrome,
which is a hypoplasia of the abdominal aorta, can also result in
reduced renal blood low. Aortic coarctation most commonly
is discovered in other ways but, if not recognized, also will cause
renovascular hypertension (Fig. 12.20).
Renal Artery Duplex Doppler Sonography
When performing renal artery duplex Doppler sonography, it is
critical to interrogate the entire extrarenal portion of the artery.
he examination is not adequate unless the entire extrarenal
portion of the main renal artery is seen and interrogated by Doppler
every 2 to 3 mm. Accessory arteries and large, early extrarenal
branches of the main renal artery are also similarly assessed. Even
then, stenoses in accessory arteries or branch renal arteries may
be missed. Fortunately, nonvisualization of branch arteries or
accessories is unlikely to afect patient management. 90,91
Visualization of the renal artery is the key to successful
ultrasound interrogation (Video 12.9). At our institution, patients
are prepared by eating a bland, low-iber diet the day before and
taking nothing by mouth (NPO) ater midnight the night before.
We ask them to avoid cafeine, smoking, and dairy products.
he sonographic examination is more likely to be successful
with a prepped patient.