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

210
ABDOMINAL ULTRASOUND
SMA
POST P
A
B
Figure 8.12 (A) Normal spectral waveform from the SMA in a fasting patient is highly pulsatile with little or no enddiastolic
flow (EDF) and reverse flow in early diastole. (B) Postprandially, the waveform becomes much less pulsatile,
with low resistance and good EDF.
in both Crohn’s and ulcerative colitis 24 compared
with normal subjects. Doppler of the SMA has
revealed an increase in flow velocities (both peak
systolic and end diastolic) and a decrease in resistance
index in numerous types of pathological
bowel, including Crohn’s. 25 However the lack of
specificity limits its use in clinical work.
Changes in resistance index have been found to
be related to the activity of Crohn’s disease, 26
which could prove valuable in monitoring patients
with known disease.
Diverticulitis may also be recognized on ultrasound
as outpouchings from the bowel wall, most
commonly affecting the sigmoid colon 11 (Fig.
8.13C). Perforation of a diverticulum may give rise
to a diverticular abscess, although the presence of air
makes ultrasound limited in its evaluation of this
condition.
Malignant tumours
The most common site for a bowel tumour in the
adult is around the caecum. It is useful to target
this area in patients with altered bowel habit in
whom bowel carcinoma is suspected, although
detection with ultrasound is usually incidental.
The mass tends to be hypoechoic, or of mixed
echogenicity, with a small, eccentric, gas-filled
lumen. This cannot be differentiated, however,
from an inflammatory mass on ultrasound. Vigorous
Doppler flow can usually be visualized in
both inflammatory and malignant masses (Fig.
8.14).
The finding of a colonic mass would normally
prompt a barium enema, to delineate the nature,
extent and position of the mass, with subsequent
staging by CT if malignancy is confirmed. The
advantage of ultrasound over barium enema is that
of displaying the tumour itself, rather than just the
narrowed lumen.
The role of ultrasound in patients with known
bowel carcinoma is to identify and document the
presence of distant metastases, particularly in the
liver, as metastases from colorectal carcinoma are
particularly amenable to curative resection.
Bowel tumours should be considered in the list
of differential diagnoses when the origin of a mass
discovered on ultrasound is unclear.
Endosonography may be used to detect and
stage rectal cancers, although it is only able to
demonstrate perirectal nodes and cannot evaluate
distant disease. Endosonography is ideal however,