Diagnostic ultrasound ( PDFDrive )

CHAPTER 8 The Gastrointestinal Tract 301
the teeth and identiication of anatomic landmarks, such as the
spleen, liver, pancreas, and gallbladder. Rotation and delection
of the transducer tip allow scanning of visualized lesions in
diferent planes. 99
Identiication, localization, and characterization of benign
masses are possible with endosonography. Varices are seen as
compressible hypoechoic or cystic masses deep to the submucosa
or in the outer layers of the esophagus, gastroesophageal junction,
or gastric fundus. 100 Benign tumors such as ibromas or leiomyomas
are well-deined, solid masses without mucosal involvement
that can be localized to the layer of the wall from which
they arise, usually the submucosa and the muscularis propria,
respectively. Peptic ulcer typically produces marked thickening
of all layers of the gastric wall, with a demonstrated ulcer crater.
Ménétrier disease produces thickening of the mucosal folds.
Staging of esophageal carcinoma involves assessment
of depth of tumor invasion and evaluation of involvement
of the local lymph nodes and adjacent vital structures. 101
Constricting lesions that do not allow passage of the endoscope
may produce technically unsatisfactory or incomplete
examinations.
Gastric lymphoma is typically very hypoechoic; its invasion
is along the gastric wall or horizontal, and involvement of
extramural structures and lymph nodes is less than with gastric
carcinoma. hus, localized mucosal ulceration with extensive
iniltration of the deeper layers suggests lymphoma, which may
also grow with a polypoid pattern or as a difuse iniltration
without ulceration. 102 Gastric carcinoma, in contrast, arises from
the gastric mucosa, is usually more echogenic, tends to invade
vertically or through the gastric wall, and frequently involves
the perigastric lymph nodes at diagnosis.
Rectum: Tumor Staging of
Rectal Carcinoma
Transrectal (endorectal) sonography is an established modality
for the staging of rectal carcinoma. 103-105 Its resolution of the
layers of the rectum surpasses the performance of both CT and
MRI. Although a variety of pathologic conditions may be assessed
with endorectal sonography, the staging of previously detected
rectal carcinoma is its major role. Patients are scanned in the
let lateral decubitus position following a cleansing enema. Both
axial and sagittal images are obtained. A variety of rigid intrarectal
probes are commercially available, using a range of transducer
technologies with phased array, mechanical sector, and rotating
crystals.
Further, we have also been routinely evaluating women with
rectal carcinoma using a transvaginal probe placed in the vagina
ater a Fleet enema. his technique is excellent, especially for
larger tumors, because the rectovaginal septum, the tumor, and
the lymph nodes in the mesorectum are more optimally seen. 106
Tumors are staged according to the Astler-Coller modiication
107 of the Dukes Classiication, or more simply with the
primary tumor component of the Union Internationale Contre
le Cancer (UICC) TNM classiication, 108 where T represents
the primary tumor, N the nodal involvement, and M the distant
metastases (Fig. 8.53).
T1
T4
FIG. 8.53 Schematic of Tumor (T) Component of TNM Staging
of Rectal Cancer on Sonography. Tumors (red) exhibit progressively
deeper invasion beginning at 10 o’clock, where T supericial noninvasive
lesion involves only supericial layers of intestinal wall. At 7 o’clock, T1
lesion invades submucosa (yellow). At 5 o’clock, T2 lesion invades
muscularis propria (blue). At 2 o’clock, T3 lesion exhibits full-thickness
invasion through layers of rectal wall, with invasion of surrounding
perirectal fat. In directly anterior aspect (12 o’clock), T4 lesion exhibits
invasion of prostate gland.
Rectal carcinoma arises from the mucosal surface of the gut.
Tumors appear as relatively hypoechoic masses that may distort
the rectal lumen. Invasion of the deeper layers, the submucosa,
the muscularis propria, and the perirectal fat produces discontinuity
of these layers on the sonogram (Fig. 8.54). Supericial
ulceration or crevices that allow small bubbles of gas to be trapped
deep to the crystal surface may demonstrate ring-down artifact
and shadowing, with loss of layer deinition deep to the ulceration.
Lymph nodes appear as round or oval, hypoechoic masses in
the perirectal fat (Fig. 8.54C). Color Doppler is an excellent
addition to transrectal probes, showing the extent of tumors on
the basis of their hypervascularity (Fig. 8.55) Infrequently, actual
deposits may be shown within enlarged nodes. herefore deinitive
staging requires pathologic assessment of both the tumor and
the regional nodes.
Limitations of rectal sonography include the following:
inability to identify microscopic tumor invasion, to image stenotic
tumors, and to image tumors greater than 15 cm from the anal
verge. It is also limited for distinguishing nodes involved with
tumor from those with reactive change and to identify normalsized
nodes with microscopic tumor invasion.
T2
T3