Diagnostic ultrasound ( PDFDrive )

CHAPTER 12 The Retroperitoneum 451
Renal Artery Aneurysm
Renal artery aneurysms are uncommon and may be saccular or
fusiform. hey can be seen with atherosclerosis or FMD. hey
are more reliably seen and followed with CT than with ultrasound.
Most renal artery aneurysms do not result in signiicant morbidity
or mortality. 99 hey grow slowly; a recent study showed a growth
rate of 0.16 mm/year. 100 Treatment should be considered if the
aneurysm is greater than 2.0 cm. Treatment is indicated if the
aneurysm is believed to be causing symptoms (e.g., hematuria,
pain, hypertension) or if the patient is a woman of childbearing
age who anticipates becoming pregnant. 100-102 he patient and
family must be made aware of a renal aneurysm to be alert to
symptoms so that diagnosis and treatment can be expedited.
Currently, no well-accepted guidelines address how oten renal
artery aneurysms should be imaged.
Mesenteric Arteries
Anatomy
hree arteries constitute the main sources of arterial blood low
to the gastrointestinal tract: celiac, superior mesenteric, and
inferior mesenteric. he celiac artery arises anteriorly from the
abdominal aorta at the level of the aortic hiatus of the diaphragm.
he celiac artery supplies blood to the spleen, pancreas, liver,
stomach, and proximal duodenum. he standard branching
pattern of the celiac artery is into the splenic and common hepatic
arteries, which are easily identiied. he third branch of the celiac
artery is the let gastric, which is much less frequently seen with
sonography. he common hepatic artery branches into the proper
hepatic artery and the gastroduodenal artery; the latter is
important as a conduit for collateral blood low to the celiac
circulatory territory when the celiac artery is highly stenosed or
occluded.
he superior mesenteric artery (SMA) typically arises from
the anterior aorta approximately 1 cm below the celiac artery
origin. he SMA supplies blood to the pancreas, distal duodenum,
jejunum, ileum, and proximal colon as far distal as the splenic
lexure. In about 20% of people, the SMA supplies some of the
hepatic blood low through a replaced or accessory right hepatic
artery. Other important branches of the SMA include the inferior
pancreaticoduodenal artery (IPDA) and the middle colic artery.
he IPDA and its branches form an arcade of blood vessels
around the head of the pancreas with the gastroduodenal
artery. 103,104 In celiac arterial occlusion, the IPDA-gastroduodenal
arcade oten becomes the primary route for blood to reach the
celiac circulation (Fig. 12.23). In cases of SMA occlusion, blood
oten lows in the opposite direction through the arcade, supplying
the occluded SMA with blood from the celiac artery.
he inferior mesenteric artery supplies the descending colon,
sigmoid colon, and superior rectum. he IMA arises from the
anterior aorta slightly to the let of midline, approximately twothirds
the distance between the renal artery origins and the aortic
bifurcation. When the aorta is viewed transversely, the IMA
arises at approximately the 1 o’clock position. Viewed longitudinally,
the appearance is similar to that of the SMA, except the
IMA is signiicantly smaller and always courses inferiorly to the
let of the aorta. Ater 1 to 2 cm, the IMA bifurcates into a
superior hemorrhoidal artery that runs caudally slightly to the
let of midline and into a let colic artery that runs laterally to
the descending colon. he let colic artery immediately divides
into ascending and descending branches. he superior hemorrhoidal
artery gives of sigmoid branches as it courses inferiorly
to the rectum (Fig. 12.24).
Connections between the SMA and IMA occur in the region
of the splenic lexure. he IMA can supply blood to the SMA
when the proximal SMA is occluded. Blood then lows from the
IMA through the marginal artery of Drummond or through the
sometimes present and more direct arc of Riolan to the middle
colic artery and then into the SMA. he middle colic artery is
an anterior branch of the SMA and is generally identiied
sonographically only in cases of SMA occlusion when it becomes
a source of collateral supply and has increased low.
Mesenteric Ischemia
Acute Ischemia. Acute mesenteric ischemia occurs when
there is an abrupt reduction of arterial low to the intestines.
he most common cause is cardiac embolus. Acute mesenteric
ischemia also may be caused by aortic dissection. Less oten,
abrupt reduction of arterial low results from SMA thrombosis,
decreased cardiac output without any obstruction of the
arterial tree, or thrombosis of the superior mesenteric vein. 105
Only a single artery needs to be compromised acutely to cause
mesenteric ischemia, most oten the SMA. Patients present
with an abrupt onset of severe abdominal pain, nausea and
vomiting, and diarrhea. Later in the course, they may develop
“currant jelly” stools from intestinal bleeding and mucosal
sloughing.
Acute mesenteric ischemia is a medical emergency. Mortality
is high, at least 50%. 106 he wide diferences in reported mortality
likely relates to the rapidity of diagnosis. Patient survival depends
on quick and accurate diagnosis and treatment. In most cases,
ultrasound has no role in the diagnosis of acute mesenteric
ischemia. 107 hese patients can be of any size and oten have a
large amount of gas in the bowel that compromises sonographic
diagnosis. In most cases, the clinician simply cannot risk wasting
time by initiating the diagnostic workup with mesenteric duplex
Doppler sonography. CTA or angiography is the test of choice. 108
ACR Appropriateness Criteria state that ultrasound “is not
recommended for initial evaluation of patients with suspected
acute mesenteric ischemia because timing of the diagnosis is
very critical.” 109
Chronic Ischemia. Duplex Doppler sonography has a more
central role in the diagnosis of chronic mesenteric ischemia.
Chronic ischemia is usually the result of atherosclerosis slowly
occluding the arteries that supply the intestines. Because the
buildup of plaque is slow, collateral circulation has an opportunity
to develop and supply some of the needed blood low to the
intestines. Mesenteric artery stenosis is relatively common,
reported in 17.5% of the independent-living older population.
Most patients with severe narrowing of one or more of the arteries
supplying the intestines have no symptoms and need no treatment.
108 hese patients maintain adequate blood low to the gut
through collateral circulation. he collateral blood low usually