Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_1410_Библиотеки_им_академика_М_И_Перельмана
.pdf
6. Diagnostic Evaluations: Radiology, Nuclear Scans 121
Fig. 6.23. CT scan showing an incarcerated hernia.
• Thickened, congested bowel with increased attenuation at the
site of obstruction associated with engorgement of the mesenteric
vasculature is concerning for strangulation.
• Other fi ndings of ischemia include lack of enhancement after
IV contrast administration or the presence of ascites.
• The presence of pneumatosis and portal venous gas are the
more ominous signs of intestinal ischemia.
Postoperative Evaluation
• It is typically used to evaluate a patient with abdominal pain, fevers,
leukocytosis, or persistent ileus in the postoperative period.
• The yield of a CT scan is greatest when it is obtained 5 days
or more after surgery. Before postoperative day 5, it is diffi cult
to differentiate normal postoperative intraperitoneal free air
or fl uid from air or fl uid that represents a leak from a hollow
viscus or infected fl uid.
• Findings highly suggestive of an anastomotic leak include an
inappropriate volume of free air or fl uid in the abdomen.
• The presence of extraluminal oral contrast confi rms a perforation of a hollow viscus.
122 The ASCRS Manual of Colon and Rectal Surgery
• The presence of localized fl uid and air around an anastomosis
are concerning for a leak but must be taken in context to the
postoperative period and the condition of the patient.
• Water-soluble enemas are more sensitive than a CT with rectal
contrast at detecting a colorectal anastomotic leak.
• An abscess is defi ned as an organized fl uid collection with or
without air that has an enhancing rim.
• CT is very good at distinguishing between an ileus and a
mechanical bowel obstruction, which is an important distinction in the perioperative period.
Other Colitides
• The CT fi ndings are very similar for all infl ammatory processes of the colon. However, their clinical presentations are
different, so combining the presenting signs and symptoms
with the distribution of CT fi ndings will usually lead to the
correct diagnosis.
• Ischemic colitis is the most common vascular abnormality of
the colon.
• The colitis may be segmental or diffuse, typically occurring
in the watershed areas of the right colon, splenic fl exure, and
rectosigmoid. CT fi ndings consist of thickened, edematous
colon in these areas (Fig. 6.24 ). The typical “thumbprinting”
in the colonic mucosa can be seen on CT scan as well as
plain fi lms.
Fig. 6.24. CT scan of ischemic colitis.
6. Diagnostic Evaluations: Radiology, Nuclear Scans 123
Fig. 6.25. CT scan of pseudomembranous colitis.
• The presence of pancolitis also tends to suggest pseudomembranous colitis versus other colitides (Fig. 6.25 ).
D. Radionuclide Imaging
• Radionuclide imaging studies base their imaging on physiology rather than anatomy, and have a wide spectrum of use in
clinical medicine.
• Radionuclide imaging studies are widely used in the diagnosis
of lower GI bleeding. The principle is that the intravascular
tracer will be extravasated into the bowel lumen during active
bleeding.
• Technetium
This radiopharmaceutical can label colloid or red blood cells
for scanning purposes.
99m
Tc is the radionuclide used in bleeding scans.
124 The ASCRS Manual of Colon and Rectal Surgery
Fig. 6.26.
the ascending colon in this patient with bleeding after a recent polypectomy.
99m
Tc-tagged red blood cell study shows early blood pool activity within
• Most centers prefer to use tagged red blood cells because lower
GI bleeds are characteristically intermittent and the opportunity to identify the active bleeding sight lasts only a few minutes
with labeled colloid.
• Focal areas of increased activity identifi ed within the lumen
of the bowel indicate that active bleeding occurred during this
acquisition period (Fig. 6.26 ). A positive scan may localize the
region of bowel that contains the bleeding site, but may not
accurately localize the specifi c site, if the bleeding is slow or
intermittent.
• Bleeding scans have greater prognostic value than diagnostic
value when the tracer is only seen on delayed images.
• The accuracy for localizing the actual bleeding site increases if
the extravasation of tracer is identifi ed within the fi rst 15–30min.
The longer it takes the tracer to accumulate, the less likely the
bleeding site will be accurately identifi ed by angiography.
• Bleeding scans are more sensitive than angiograms in the detection of lower GI bleeding. The required rates of bleeding for
detection are lower for bleeding scans (0.1–0.2mL/min) than
for angiograms (0.5mL/min). The early (within 3min) detection
of intraluminal tracer indicates a high likelihood of successful
arteriographic localization of the bleeding site. For this reason,
some interventional radiologists require a positive scan before
performing angiography.
• If the patient is hemodynamically unstable and rapidly bleeding,
some centers may prefer to go directly to arteriograms because
the time involved in pretest preparation for tagged red blood
scans may be too lengthy.
6. Diagnostic Evaluations: Radiology, Nuclear Scans 125
E. Arteriography
• The arteriogram is a useful diagnostic and therapeutic modality
in the treatment of active lower GI bleeding. If a radionuclide
scan is performed and localizes the site of bleeding, a selective
angiogram can then be performed.
• For bleeding localized to the left colon on tagged RBC study,
the inferior mesenteric artery is selected fi rst. The superior
mesenteric artery is selected fi rst for those bleeds that occur
in the right colon. If the bleeding site is not identifi ed after
injection of both the superior and inferior mesenteric arteries, a
celiac run is performed looking for an upper intestinal bleeding
source.
• Active bleeding can be diagnosed by the accumulation of
contrast in the arterial phase that persists through the venous
phase (Fig. 6.27 ).
• Bleeding needs to occur at a higher rate for a positive angiogram
(0.5mL/min) than for nuclear imaging (0.1–0.2mL/min).
• Diverticulosis and vascular ectasias are presumed to be the
leading cause of lower GI bleeding in most patients. Diverticular bleeds appear as a blush of contrast contained within a
Fig. 6.27. Mesenteric angiogram shows pooling of contrast in the sigmoid colon
in this patient with surgically proven diverticular bleeding.
126 The ASCRS Manual of Colon and Rectal Surgery
diverticulum. Vascular ectasias often occur in the right colon
and appear as small vascular clusters, a blush in the wall of the
colon and early opacifi cation of a draining vein.
• Postpolypectomy bleeding has been diagnosed and treated
with angiography. A rapid blush of dye occurs at the site of
bleeding and often stops with direct infusion of vasopressin or
embolization (Fig. 6.28 ).
• Acute mesenteric ischemia is one of the most common intestinal disease processes for which arteriography is used for
diagnosis and treatment.
• Acute mesenteric ischemia can be either nonocclusive or occlusive. The typical early angiographic images show diffuse vasoconstriction of mesenteric arterial branches and decreased
parenchymal vascularity (Fig. 6.29 ).
• The diagnostic percutaneous catheter can be used to treat
the mesenteric phase of constriction with IV glucagon or
intraarterial infusion of the papaverine in an intensive care
unit setting.
• An arteriogram is the most useful diagnostic examination for
patients in whom one has a high clinical suspicion of acute
occlusive mesenteric ischemia.
• A superior mesenteric artery embolus typically lodges just
proximal or distal to the take off of the middle colic artery and
is seen as a meniscus at the site of occlusion and blockage of
contrast (Fig. 6.30 ).
F. CT Colonography
• CT colonography is rapidly developing as a noninvasive total
colonic examination for the detection of colon polyps and cancers.
• This technique uses volumetric data acquired by helical CT
scanners and workstations which use two- and three-dimensional
images to evaluate data.
• Although the colon is evaluated in a noninvasive way, a bowel
preparation is still required the day before the examination to
eliminate formed fecal matter. Air insuffl ation is done via a
small tube placed within the rectum to distend the bowel and
to minimize folds within the colonic wall.
6. Diagnostic Evaluations: Radiology, Nuclear Scans 127
a
b
Fig. 6.28. Mesenteric angiogram shows extravasation of contrast A indicating
an acute bleed that was successfully treated after infusion of pitressin B.
Fig. 6.29. Mesenteric angiogram shows vasoconstriction and pruning of the
superior mesenteric artery and its branches in this patient who presented with
mesenteric ischemia secondary to severe hypotension.
Fig. 6.30. Mesenteric angiogram shows a large fi lling defect within the proximal superior mesenteric artery consistent with an embolism in this patient with
ischemic bowel.
6. Diagnostic Evaluations: Radiology, Nuclear Scans 129
• Several studies have compared CT colonography to colonoscopy for high- and low-risk patients. The sensitivity of this
technique per individual patient ranges from 75 to 100% and
the specifi city ranges from 72 to 100%.
• In randomized, controlled trials, the specifi city is greater for
polyps larger than 1cm than for polyps larger than 5mm.
• The main limitation of CT colonography has been distinguishing
polypoid tissue from fecal matter and the detection of fl at lesions.
• Currently, most centers are using CT colonography for those
patients who have had incomplete colonoscopies or who cannot undergo colonoscopy for medical reasons.
G. Positron Emission Tomography (PET)
• This technique uses [18F] 2-fl uoro-2-deoxy- d -glucose (FDG)
which is a radiopharmaceutical glucose analog to measure
increased glucose uptake and metabolism in rapidly dividing cells. Malignant and other rapidly dividing cells that have
a high metabolic rate will take up FDG for use as a glucose
substrate.
• The imaging technique of PET utilizes differences in uptake of
FDG in malignant versus benign cells. The intracellular accumulation concentrates the radiopharmaceutical analog, which
appears “bright” upon imaging (Fig. 6.31 ).
• FDG PET has been used to evaluate metastatic disease and to
improve staging accuracy (Fig. 6.32 ). This technique images
the whole body and is more sensitive than CT for the detection
of hepatic and extrahepatic colorectal cancer metastases and
the detection of local recurrence. The reported sensitivities for
PET detection of liver metastases range from 89 to 95% and
for extrahepatic metastases 87–92%.
• The use of FDG PET versus CT or MRI is based on the premise
that functional differences in tumor appear before size changes.
• A positive FDG PET scan in the setting of no infl ammation
would indicate a local recurrence of a rectal cancer.
• Furthermore, detection of small extrapelvic metastases is more
accurate using FDG PET than CT or MRI.
• Thus, the use of FDG PET for staging or recurrent cancers may
help plan or avoid expensive and possibly more morbid surgical
procedures.
130 The ASCRS Manual of Colon and Rectal Surgery
a
b
Fig. 6.31. Axial attenuation corrected PET image A and fusion PET CT image
B show an area of intense FDG uptake in the right hepatic lobe consistent with
hepatic metastatic disease in this patient with cecal adenocarcinoma.
• The cellular glucose metabolism is also increased in infl ammation as the increased uptake of FDG can be seen in leukocytes
and macrophages. Infl ammatory processes such as diverticulitis
and pneumonia can lead to false-positive readings thus making
it imperative to correlate positive PET fi ndings with the clinical
picture and conventional radiologic evaluation.
• Detection of metastatic disease is dependent on the size and
degree of metabolic activity. Limited spatial resolution may
lead to false-negative readings for small, <1-cm lesions.
Соседние файлы в папке Библиотека им академика М.И. Перельмана