Diagnostic ultrasound ( PDFDrive )

290 PART II Abdominal and Pelvic Sonography
found singly and in the right colon, where no association with
muscular hypertrophy or dysfunction has been established.
Inspissated fecal material is believed to incite the initial
inlammation in the apex of the diverticulum leading to acute
diverticulitis. 73 Spread to the peridiverticular tissues and microperforation
or macroperforation may follow. Localized abscess
formation occurs more oten than peritonitis. Fistula formation,
with communication to the bladder, vagina, skin, or other bowel
loops, is present in a minority of cases. Surgical specimens
demonstrate shortening and thickening of the involved segment
of colon, associated with muscular hypertrophy. he peridiverticular
inlammatory response may be minimal or extensive.
Sonography appears to be of value in early assessment of
patients thought to have acute diverticulitis. 74,75 Classic features
include segmental thickened gut and inlamed diverticula and
inlamed perienteric fat. A negative scan combined with a low
clinical suspicion is usually a good indication to stop investigation.
However, a negative scan in a patient with a highly suggestive
clinical picture justiies a CT scan. Similarly, demonstration of
extensive pericolonic inlammatory changes on the sonogram
may be appropriately followed by CT scan to deine better the
nature and extent of the pericolonic disease before surgery or
other intervention.
Because diverticula and smooth muscle hypertrophy of the
colon are so prevalent, it seems likely that they would be frequently
seen on routine sonography, but this is not the usual experience.
However, with the development of acute diverticulitis, both the
inlamed diverticulum and the thickened colon become evident.
Presumably, the impacted fecalith, with or without microabscess
formation, accentuates the diverticulum, whereas smooth muscle
spasm, inlammation, and edema accentuate the gut wall thickening.
Identiication of diverticula on the sonogram strongly
indicates diverticulitis. 76
Diverticula are arranged in parallel rows along the margins
of the teniae coli, so careful technique is required to make
their identiication. Ater demonstration of a thickened loop
of gut, the long axis of the loop should be determined (Fig.
8.38). Slight tilting of the transducer to the margins of the
loop will increase visualization of the diverticula, because they
may be on the lateral and medial edges of the loop rather than
directly anterior or posterior (Fig. 8.39). Cross-sectional views
are then obtained along the entire length of the thickened
gut. Abnormalities must be conirmed on both views. Errors
related to overlapping gut loops, in particular, can be virtually
eliminated with this careful technique. Identiication of diverticula
on sonography is correlated highly with inlammation,
because it is unusual to show the diverticula in the absence of
inlammation (Fig. 8.40).
Failure to identify gas-containing abscesses or interloop
abscesses is the major source of error when using sonography
to evaluate patients with suspected diverticulitis. he meticulous
technique of following involved thickened segments of colon in
long-axis and transverse section will help detect even small
amounts of extraluminal gas.
Sonographic features of diverticulitis include segmental
concentric thickening of the gut wall that is frequently strikingly
hypoechoic, relecting the predominant thickening in the muscle
layer; inlamed diverticula, seen as bright, echogenic foci with
acoustic shadowing or ring-down artifact within or beyond the
thickened gut wall; acute inlammatory changes in the pericolonic
fat, seen as poorly deined hyperechoic zones without obvious
gas or luid content (Fig. 8.41, Video 8.15); and abscess formation,
seen as loculated luid collections in an intramural, pericolonic,
or remote location. With the development of extraluminal
inlammatory masses, the diverticulum may no longer be identiied
on sonography, presumably being incorporated into the
inlammatory process. herefore demonstration of a thickened
segment of colon with an adjacent inlammatory mass may be
consistent with diverticulitis, but also with neoplastic or other
inlammatory disease. Intramural sinus tracts appear as highamplitude,
linear echoes, oten with ring-down artifact, within
the gut wall. Typically, the tracts are deep, between the muscularis
propria and the serosa. Fistulas appear as linear tracts that extend
from the involved segment of gut to the bladder, vagina, or
adjacent loops. heir echogenicity depends on their content,
usually gas or luid. hickening of the mesentery and inlamed
mesenteric fat may also be seen (Fig. 8.41).
he sonographic and clinical features of diverticulitis are more
speciic than those of acute appendicitis, and errors of diagnosis
occur less oten. However, torsion of appendices epiploicae
(omentales) may produce a sonographic appearance so closely
resembling acute diverticulitis that diferentiation may be dificult.
76 he inlamed or infarcted fat of the appendix shows as
shadowing of increased echogenicity related to the margin of
the colon, mimicking an inlamed diverticulum. However, regional
perienteric inlammatory change is usually minimal, with fewer
systemic symptoms. he noninlamed colonic appendices epiploicae
are not visible, except with ascites, where they are seen
as uniformly spaced, echogenic foci along the margins of the
colon.
Sonography of Diverticulitis
GUT
Segmental concentric thickening of wall
Hypoechoic relecting muscular hypertrophy
INFLAMED DIVERTICULA
Echogenic foci within or beyond gut wall
Intramural sinus tracts
High-amplitude linear echoes within gut wall
Acoustic shadowing or ring-down artifact
PERIENTERIC SOFT TISSUE
Inlammation of pericolonic fat
Hyperechoic mass effect
Thickening of the mesentery
Abscess formation
Loculated luid collection
Often with gas component
Fistulas
Linear tracts from gut to bladder, vagina, or adjacent
loops
Hypoechoic or hyperechoic