9%20ECOGRAFIA%20ABDOMINAL%20COMO%20CUANDO%20DONDE

THE RETROPERITONEUM AND GASTROINTESTINAL TRACT 199
D
Figure 8.3 cont’d
the aortic lumen.
E
(D) TS and (E) LS of a dissecting aortic aneurysm. The detached intimal flap is clearly seen within
correct plane, regardless of vessel tortuosity, is a distinct
advantage over CT, which may over- or underestimate
the size of the aneurysm in an axial plane.
Complications of aortic aneurysm
Dissection of the aneurysm, in which the intima
becomes detached, is uncommon in the abdomen.
Ultrasound may visualize the intimal flap and the
false lumen created between the media and intima
often contains slower, more turbulent or even
reversed flow. Layers of thrombus may mimic a dissection,
and colour flow Doppler is particularly
useful in such cases.
Leakage of an aneurysm may cause retroperitoneal
haematoma, but CT is usually more reliable
in detecting leaks than ultrasound.
Rupture of an aortic aneurysm is not unknown
in the ultrasound department or emergency
department, and is accompanied by abdominal
pain and severe hypotension. It is associated with a
high mortality rate and is a surgical emergency.
Involvement of the renal arteries may cause
renal artery thrombosis and subsequently small
kidney(s). Always check the kidneys at the time of
scanning to ensure they are of normal size and
appearance.
THE INFERIOR VENA CAVA (IVC)
Ultrasound is highly successful in demonstrating
the proximal IVC, by using the liver as an acoustic
window, especially if the patient is turned right
anterior oblique. The distal IVC may be obscured
by overlying bowel gas and, unlike the aorta, is also
susceptible to compression, making visualization
difficult in some cases.
The normal IVC has thinner walls and a more
flattened profile than the aorta, and its lumen alters
with changing abdominal pressure; for example,
during respiration the lumen decreases on inspiration,
or with the Valsalva manoeuvre (Fig. 8.4). Its
course becomes slightly anterior as it passes
through the diaphragm, unlike the aorta which
travels posteriorly at this point.
The main renal veins may be seen in TS, entering
the IVC just below the level of the pancreas
(Fig. 8.2).
Haemodynamically, the blood flow spectrum
from the IVC alters according to the distance of
the sample volume from the right atrium (Fig. 8.4
F, G). The blood flow through the IVC and proximal
hepatic veins is pulsatile, with reverse flow
during right atrial systole. Pulsatility reduces in the
distal IVC.