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improved outcomes in colon and rectal surgery
Figure 11.31 Appendix Mucocele. Axial MDCT demonstrates distension of the
appendix with mucus.
Appendix
Acute Appendicitis
MDCT has a high sensitivity (91–100%) and specificity (91–
99%) in diagnosing acute appendicitis (123–126). The diagnosis
of acute appendicitis is based on finding: an abnormally dilated
(>6 mm), enhancing appendix; appendix surrounded by inflammatory periappendiceal fat stranding; focal thickening of the
base of the cecum; periappendiceal abscess; or obstructing calcified appendicolith (Figures 11.30A and 11.30B). The most common reason for a false-negative diagnosis is related to a paucity of
intraabdominal fat often seen in pediatric patients and patients
with a lean body habitus.(127–130) Optimal cecal opacification and distention are important because without cecal opacification a distended appendix can be mistaken for a small-bowel
loop.(131, 132) Therefore, intravenous, oral, and rectal contrast
should be used. Appendicitis may cause reactive dilatation of the
small bowel and mimic a small-bowel obstruction, resulting in
a missed diagnosis of the underlying problem. In addition, the
dilated small bowel impedes the flow of oral contrast, so that
opacification of the cecal region is suboptimal, creating difficulty
in diagnosis. Therefore, a small-bowel obstruction in patients
who have no history of surgery or cause for obstruction is suspicious for appendicitis, especially in younger patients.(130)
Figure 11.32 Lipoma. Axial MDCT demonstrates a 2–3 cm, round, sharply
defined tumor with homogenous fat density (-80 to -120 H) adherent to the
sigmoid colon.
(CTA) has become the method of choice for imaging the pulmonary vasculature, and has replaced invasive pulmonary angiography as the reference standard for diagnosis.(112–117) Another
advantage of CTA over pulmonary angiography is the ability to
identify alternative or additional diagnosis such as: atelectasis,
pneumonia, pulmonary edema, pleural, and pericardial effusions,
and many others. CT venography (CTV) combined with CTA
can be used as a comprehensive examination of the deep venous
system to detect both PE and deep vein thrombosis (DVT). CTV
is performed by scanning of the pelvis from the iliac crest to the
popliteal fossa approximately 120 s after completion of the CTA.
CTV could potentially salvage the occasional suboptimal PE study
by diagnosing a DVT and guide interventions such as vena cava
filter placement. Numerous studies have cited 97% agreement
between CTV and US.(118–122) The addition of CTV increases
the gonadal radiation exposure, and should be used selectively
on the basis of risk-benefit considerations (e.g., avoided in young
patients and reproductive female patients).(116)
Mucocele and Tumors of the Appendix
Mucocele refers to distension of all or a portion of the appendix
with mucus secondary to obstruction by appendicolith, adhesions,
or tumor.(133) Most commonly, this lesion is a retention mucocele
and is asymptomatic (Figure 11.31). Some cases are caused by mucinous cystadenomas or cystadenocarcinomas of the appendix.(133,
134) Continued secretion of mucus produces a large (up to 10 cm),
well-defined, cystic mass in the right lower quadrant, which may
have a thin rim of wall enhancement or calcification.(135) Rupture
of the mucocele may result in psuedomyxoma peritonei causing
gelatinous implants and mucinous ascites throughout the peritoneal
cavity. Although an enhancing nodular component is concerning
for malignancy (136), neoplastic and retention mucoceles cannot
be reliably distinguished by imaging studies. Adenocarcinoma of
the appendix is rare and is usually discovered in the clinical setting
of suspected appendicitis in an older adult. Imaging demonstrates a
soft tissue mass within or replacing the appendix.(133) Lymphoma
of the appendix appears similar to appendicitis, but is typically larger
with a diameter of 3 cm or greater.(137)
Carcinoid is the most common tumor of the appendix
accounting for 85% of all tumors.(133) Carcinoid of the appendix usually appears as a focal enhancing mass in the distal
appendix.(133, 138) Carcinoid metastases to mesentery and
the liver enhance brightly on arterial phase imaging because of
their vascularity.(138–146) Three-dimensional CT angiography
is useful to fully appreciate the mesenteric mass and its relationship to the vessels, which is important for surgical planning.
(140–147) In addition to the liver, metastases can be seen on CT
in the lung and bones.
Other Tumors of the Colon
CT remains the imaging study of choice for detection of benign
and malignant tumors of the colon other than adenoma and
1
limitations of colorectal imaging studies
Figure 11.33 GIST. Axial MDCT demonstrates a large heterogenous exophytic
mass with cystic degeneration and necrosis that communicates with the lumen of
adjacent colon and small bowel.
adenocarcinoma. Metastases to the colon can be seen on contrast enhanced MDCT, if they are large enough; but CT cannot
differentiate primary tumor from metastasis.(148) One of the
most common benign colonic tumors is a lipoma. Lipomas can
be easily diagnosed by demonstrating a 2–3 cm, round or ovoid,
sharply defined tumor with homogenous fat density (-80 to -120 H)
(Figure 11.32).
Colonic lymphoma usually appears as either a marked thickening of the bowel wall that often exceeds 4 cm, or a homogeneous
soft-tissue mass without calcification. Lymphoma characteristically causes much larger soft-tissue masses than adenocarcinoma.
Owing to the softness of the tumor, the lumen is commonly
dilated or normal, rather than constricted, and bowel obstruction
is uncommon. The absence of desmoplastic reaction and diffuse
lymphadenopathy help to differentiate lymphoma from adenocarcinoma.(149–150)
Gatrointestinal Stroma Tumors (GIST) can be benign or
malignant and cannot be diffentiated on cross sectional imaging
without distant metastases to the liver or peritoneum.(151) GISTs
can appear as an exophytic or intraluminal mass, and size varies from millimeters to 30 cm. Cystic degeneration, hemorrhage,
and necrosis are common in large lesions with calcification rarely
noted (Figure 11.33). The tumor cavity may communicate with
the colon lumen and contain air or oral contrast. Sarcomas that
arise in the bowel, anorectum, or omentum are indistinguishable
from malignant GIST.(151) Tissue types include leiomyosarcoma,
fibrosarcoma, and liposarcoma.
Figure 11.34 Small Bowel Obstruction. Axial MDCT demonstrates multiple
dilated loops of small bowel with air fluid levels. Intraluminal fluid distends the
bowel and acts as a natural contrast agent.
Figure 11.35 SBO from Adhesions. Axial MDCT of same patient in Figure 11.II-
L-1 shows abrupt transition from dilated to nondilated bowel suggests adhesions
as the cause. A suture line from the patient’s colonic resection and ileocolonic
anastomosis is seen.
right abdomen. The axis of torsion is in the ascending colon above
the ileocecal valve. Signs of bowel ischemia include benign wall
thickening, “thumbprinting”, inflammation of pericolic fat, and
pneumatosis (air in the bowel wall).(152)
Sigmoid and Cecal Volvulus
Diagnosis of large bowel volvulus is usually made by plain radiographs or fluoroscopy, but CT is used to detect evidence of ischemia. Sigmoid volvulus is seen on CT as distended colon with the
mesenteric twist appearing as a “whirl.” Cecal volvulus has a similar
appearance with the apex of the distended colon pointed toward
the right lower quadrant and the “whirl” of cecal mesentery in the
Small Bowel Obstruction
Accuracy of Diagnosis and Causes of SBO
CT has gained favor as the initial radiologic examination of
patients with SBO because it can often determine the cause,
severity, and transition point of obstruction.(153–158) The sensitivity of CT for high-grade SBO is 90–96%, with a specificity of
1
improved outcomes in colon and rectal surgery
Table 11.5 CTC laxative preparations.
Laxative Agent Limitations
Figure 11.36 Ileocecal Intussusception. Axial MDCT CT demonstrates
characteristic findings of the distal segment (intussuscipiens) dilated with a
thickened wall. Its lumen contains an eccentric, soft-tissue mass (intussusceptum)
with an adjacent crescent of fat density that represents the invaginated mesentery.
Sodium Phosphate
Magnesium Citrate
Polyethylene Glycol (PEG)
Because of rare reported instances of acute
phosphate nephropathy, avoid use in
elderly with hypertension, patients
taking angiotensin-converting enzyme
inhibitors, and patients with renal or
cardiac insufficiency (184).
Avoid in severely compromised patients who
cannot tolerate mild fluid or electrolyte
shifts.
Most favorable safety profile but poorest
adherence because of the consistency,
taste, and large volume (4 L) that must be
ingested.
collapsed and this should not be mistaken for evidence of a transition zone. CT is reported to be less accurate in patients with
low-grade or partial SBO and it may be difficult to distinguish
between a SBO and paralytic or adynamic ileus. In such cases the
“small bowel feces” sign, which is gas bubbles mixed with particulate matter in the dilated bowel, is a reliable indicator of a SBO.
(161–166) If oral contrast reaches the colon, a complete SBO is
not present.
CT Enteroclysis
CT enteroclysis is useful in the evaluation of equivocal cases,
and is performed by placing a tube in the fourth portion of the
duodenum with infusion of 1 to 1.5 L of dilute contrast into the
small bowel. The addition of coronal reformations is a valuable
adjunct to the transverse scans because it improves identification
and exclusion of bowel obstruction.(167)
Figure 11.37 Pneumatosis Intestinalis. Small bowel ischemia is suggested by the
decreased segmental bowel-wall enhancement and pneumatosis intestinalis.
91–96%.(153, 157, 159–165) The 3, 6, and 9 rule can be used to
detect bowel dilatation on CT scans. Oral contrast is not always
necessary as the intraluminal fluid distends the bowel and acts as
a natural contrast agent (Figure 11.34). Oral contrast should be
avoided in patients with a high grade or complete SBO. Adhesions
cause 50% to 75% of SBOs, but are often not directly visualized
by CT. Beaklike narrowing or abrupt transition from dilated to
nondilated bowel suggests adhesions as the cause (Figure 11.35).
Obstruction from tumor, abscess, intussusception (Figure 11.36),
inflammation, and hernia are readily diagnosed with CT.
Paralytic/Adynamic Ileus
Paralytic or adynamic ileus appears as dilation of small bowel
without a transition zone. The colon may be distended or
Closed Loop Obstruction, Strangulation, and
Intestinal Ischemia
CT can diagnose closed loop obstruction of the small bowel
and bowel ischemia. The “beak” or “whirl” sign may be seen at
the obstruction and volvulus.(168) Dilated bowel loops with
stretched and prominent mesenteric vessels converging on a site
of obstruction suggest a closed loop obstruction. Decreased segmental bowel-wall enhancement and pneumatosis (Figure 11.37)
are associated with small-bowel ischemia.(169) The diagnosis of
small-bowel ischemia in the presence of obstruction has reported
sensitivities varying from 75% to 100%, and specificities of 61%–
93%.(170–174)
COMPUTED TOMOGRAPHIC
COLONOGRAPHY (CTC)
Colorectal Cancer Screening and the
Advanced Adenoma
Computed tomographic colonography (CTC) or Virtual Colonoscopy is an excellent technique for the detection of colorectal
polyps and cancer. Because colorectal cancer has an identifiable
precursor lesion, the advanced adenoma (polyp), there is a genuine opportunity for prevention rather than detection alone.
11
limitations of colorectal imaging studies
(216, 217) CTC’s sensitivity for polyp detection is similar to
(175) or better than (176) double-contrast barium enema. CTC
has accuracy similar to that of optical colonoscopy (OC) both
in high-risk groups (177–180) and in a low-prevalence screening population (181). Also, CTC has the potential to become an
accepted technique for evaluation of the nonvisualized part of
the colon after incomplete OC.(182)
CT Colonography (CTC) Technique
Adequate CTC software is critical for accurate interpretation,
but even the best software system will fail if colonic preparation
is inadequate. Colonic preparation involves a clear liquid diet the
day before the exam and a laxative for catharsis.(183) The laxative
for a standard CTC bowel preparation is sodium phosphate, which
is used in nearly 90% of cases (Table 11.5).(183) Dilute barium is
used to tag residual feces, and water soluble diatrizoate serves the
dual purpose of uniform fluid tagging and secondary catharsis.
(185) Gaseous distention can be achieved with room air or CO2,
and the insufflations can be automated or manually controlled by
the patient or the medical staff (technologist or physician). Both
supine and prone axial scans are obtained with 3D software reconstructions. At least 8 to 16 detector CT is needed with 1.25 mm
collimation (Figures 11.38 and 11.39).
Benefits, Complications, and Limitations of
CT Colonography (CTC)
CTC does not involve the sedation or recovery time associated with
OC. With the short scan time of MDCT scanners, patients must
tolerate maximum inflation for only a few seconds, as opposed to
OC and barium enema. A survey of patients undergoing colorectal cancer screening found that patients prefer CTC over OC and
barium enema.(186) Unlike colonoscopy and barium enema, CTC
allows visualization of organs outside the colon. Although nonenhanced CTC (at one-fourth the standard radiation dose) is not
adequate for screening, all solid abdominal and pelvic pathology,
important disease such as abdominal aortic aneurysm, renal cell
carcinoma, ovarian cancer, and other neoplasms can be detected.
The most beneficial situation would be the discovery of an asymptomatic early process that could be cured with early treatment. The
safety profile of CTC has been extensively reviewed. The largest
U.S. study, the combined Working Group on Virtual Colonoscopy
(187), found that CTC was a very safe, noninvasive procedure
(Table 11.6) By combining the Working Group results with two
other large multicenter studies (188–189), the total number of
CTC examinations exceeds 50,000. None of the cases of perforation from these three groups resulted in patient death. Many cases
of CTC–related perforation have involved high-risk symptomatic
patients for whom OC was either incomplete or contraindicated.
No cases of symptomatic perforation resulted from patient-controlled insufflations or automated CO2 delivery. Staff-controlled
manual insufflations lack the inherent safeguards of the other
two methods and have accounted for virtually all known cases
Figure 11.38 Normal CTC Supine Axial 2D Images.
Table 11.6 Working group on virtual colonoscopy experience
(187) — (21,923 CTC performed between 1997 and 2005).
Screening CTC (11,707 patients) Diagnostic CTC (10,216 patients)
No cases of perforation
Note: Overall complication rate of 0.02%
Symptomatic perforation rate of 0.005% (one in 21,923 patients).
The 1 patient in 21,923 with a symptomatic perforation was a patient with known
annular carcinoma of the sigmoid colon who was already symptomatic prior to
CTC, and massive pneumoperitoneum was found after a few puffs of air were
delivered.(187)
2 cases of perforation (1 asymptomatic,
1 symptomatic)
Figure 11.39 Normal CTC 3D Image of the
Colon.
111
improved outcomes in colon and rectal surgery
Table 11.7. Results from Kim et al.(195)
Variable
Use of OC
# of Advanced Adenomas
>10 mm 103 103
6–9 mm 5 11
<5 mm 1 3
Invasive Carcinoma 14 4
Note: Only 3 subcentimeter polyps with high-grade dysplasia (0.05%), and there
were no subcentimeter cancers.
Total of 2,006 polypectomies to remove diminutive polyps (<5 mm), which
yielded only 4 advanced lesions (0.2%).
Primary CTC
(n = 3,120)
246 3,163
Primary OC
(n = 3,163)
of symptomatic perforation. The risk of perforation with automated or patient-controlled distention methods approaches zero
among asymptomatic adults.(190) The automated CO2 delivery is
not only safe but also results in improved colonic distention and
reduced spasm.(191)
Although the capability of CTC to depict polyps is both operator and technique dependent, this modality has a relatively high
specificity.(176, 178–181) Some of the inconsistent results in previous studies have been attributed to reader inexperience, inappropriate protocol, and lack of image software technology. CTC
trials involving cohorts with protocols restricted to a primary 2D
approach fared poorly (192–194), whereas those that relied on
2D and 3D polyp detection performed well (178–181, 195).
Primary CT Colonography Screening with Selective Optical
Colonoscopy
CTC cannot replace optical colonoscopy (OC), as it is an essential
diagnostic tool for the nonsurgical removal polyps. As a screening
test applied to asymptomatic adults; however, OC is a relatively
invasive procedure, with reported perforation rates of 0.1–0.2%.
(196–200) Given that a small minority of screening patients actually harbors a clinically relevant lesion (181, 201–206), the high
rate of negative screening studies may come into question now
that a less invasive alternative, CTC, is becoming widely available
and greatly improved from the past. Therefore, primary CTC with
selective OC deserves consideration as a preferred screening strategy. In this approach patients are screened with CTC and patients
with polyps >10 mm are offered same-day OC with polypectomy.
Patients with polyps 6 to 9 mm are given the option of CTC surveillance or OC with polypectomy. To avoid any confusion, or
anxiety, potential diminutive lesions (≤5 mm) are not reported.
In a large screening study of asymptomatic adults by Kim et al.
(195) (Table 11.7) found that CTC and OC screening methods
resulted in similar detection rates for advanced neoplasia within
the same general population. The results of this study also suggest that a 10 mm threshold for polypectomy at asymptomatic
screening would probably capture the vast majority of clinically
relevant lesions. The study noted scarcity of small advanced
neoplastic lesions and marked decrease in the use of OC and
total rates of polypectomies in the CTC group (Table 11.7);
which suggests that this screening approach is a safe, clinically
effective, and cost-effective filter for therapeutic OC.(195) Markov
modeling of large cohorts has also shown that the strategy of not
reporting diminutive polyps (<5 mm) during CTC screening is a
cost-effective approach that can substantially reduce the rate of
polypectomy and complications without any sacrifice with respect
to cancer prevention.(204) However, the clinical management of
polyps 6 to 9 mm that are detected during CTC is controversial.
One approach is to offer OC for polypectomy to all patients with
polyps >6 mm.(207) An option of short-term CTC surveillance
for patients with one or two small CTC-detected polyps has also
been suggested.(208) Potential benefits include the decreased use
of resources, procedural risks, and cost. Potential drawbacks are
the possibility of following a polyp that harbors a focus of cancer.
Ultimately, more investigation will be needed to determine which
strategy is more beneficial for polyps <10 mm that are found
during CTC. Furthermore, by combining CTC and OC screening efforts, the overall screening compliance could substantially
increase.(192)
CT Colonography Follow-Up after Surgery
for Colorectal Cancer
More than half of colorectal cancer recurrences are distant metastases to the liver and lungs (209, 210) and most local recurrences
lack an intraluminal component (210). CTC is usually performed
without IV contrast for screening, but CTC performed with
IV contrast enhancement could accomplish the dual function
of annual CT surveillance of the abdomen and liver, as well as
examination of remaining colonic lumen. CTC could also have
a role in postsurgical patients in whom optical colonoscopy has
failed or in patients with a colostomy. The limitations of CTC
in the postoperative patient include extrusion of surgical staples,
inflammatory polyps, and benign ulcers. Extruded staples can
be clearly distinguished from true polyps on 2D images by their
high attenuation.(211) Because inflammatory polyps and benign
ulcers are not distinguishable from adenomatous polyps on CTC,
follow-up OC and biopsy will be needed.(211) Nevertheless, it
would be efficient if CTC could eliminate through screening
those patients whose colon is normal, while also performing the
dual function of evaluating the entire abdomen for metastatic
disease. Also, the ability of IV contrast enhanced CTC to provide
images of the bowel wall, extracolonic tissues, lymph nodes, and
liver in one setting may provide a more accurate preoperative
staging of colorectal cancers.(212, 213) A recent study found that
CTC colorectal cancer T staging overall accuracy was 73–83%,
and N staging was associated with an overall accuracy of 80%.
(214) Thus, contrast-enhanced CTC is a fairly accurate technique
for preoperative staging of colorectal tumors.(212, 213)
FLOUROSCOPY
Barium Enema
Single and Double Contrast Barium Enema (DCBE)
Single Contrast Barium Enema is performed by filling the rectum
and colon with barium through an enema catheter after inflating a retention rectal balloon. Double Contrast Barium Enema
(DCBE) or Air Contrast Barium Enema (ACBE) is performed
similarly, except the colon is partially filled with undiluted
11
limitations of colorectal imaging studies
Figure 11.40 Annular Carcinoma. DCBE demonstrates an annular “apple core”
stricture characterized by circumferential narrowing of the bowel with mucosal
destruction and shelf-like, overhanging borders.
barium. Once the barium reaches the middle transverse colon, the
enema bag is lowered to the floor and the rectum is drained by
gravity. Using a pneumatic bulb, room air is insufflated into the
colon. The radiologist manipulates the amount of air insufflated;
and analyzes the barium-coated mucosal surface to detect abnormalities. Fluoroscopic guidance allows the radiologist to optimize technical components. Afterwards, overhead radiographs
are obtained in projections that the radiologist cannot obtain at
fluoroscopy. Both single and DCBE can identify malignant strictures, but the double contrast of air and barium provides better
visualization of the mucosa and colon polyps.(215) The radiographic appearance of the lesion depends on the profile in which
the lesion is imaged and the location of the lesion relative to the
barium pool. It is not possible to distinguish between the sporadic
adenomatous polyps and polyposis syndromes using contrast
studies.(216) The appearance of polyps and early cancers can
be sessile, polypoid pedunculated, or carpet lesions. Colorectal
carcinomas may manifest as polypoid, semiannular, or annular
strictures. Annular strictures are characterized by circumferential
narrowing of the bowel, with overhanging borders referred to as
“apple core” lesions (Figure 11.40). Benign strictures from ischemic, infectious, and inflammatory processes, in contrast, tend to
have smooth, tapering borders. The positive predictive value for
malignant strictures on DCBE is 96% (sensitivity, 63–66%) and
the positive predictive value for benign strictures is 84–88% (sensitivity, 88–86%, respectively).(217) On occasion, however, the
area of narrowing in diverticulitis may have more abrupt borders
and may mimic the appearance of tumor. If the barium enema
examination reveals equivocal findings, colonoscopy should be
performed after treatment for diverticulitis to rule out an underlying carcinoma. When annular carcinomas are nonobstructive,
it usually is possible to perform DCBE so that the colon may
be evaluated for other synchronous neoplasms. Performance
of DCBE should not be performed in patients with large bowel
obstruction, acute colitis, or when there is concern for bowel perforation, as barium can cause peritonitis. In these situations, a
water-soluble contrast agent should be used.(216)
Limitations of Double Contrast Barium
Enema (DCBE)
DCBE is a valuable tool in colorectal cancer screening, but the
examination is not without limitations. When lesions are missed,
both perceptive/interpretive and technical errors are responsible.
(218, 219) Perceptive/interpretive errors occur when lesions are
overlooked because of superimposed bowel loops or are hidden
by deep haustral folds. Also, polyps that are small and flat or that
directly abut a haustral fold may be subtle. Another area that may
pose perceptive diagnostic difficulties is the ileocecal valve. While
some carcinomas arising at the ileocecal valve may be obvious
polypoid lesions, others may manifest as relatively subtle splaying or distortion of the valve.(220) Incompetence of the ileocecal
valve can degrade the quality of barium enemas by preventing
full colonic distention and allowing the small bowel to obscure
segments of the colon.
Internal hemorrhoids appear either as thickened, undulating
folds that extend 3 cm or less from the anorectal verge or as a
cluster of small submucosal nodules that has been likened to the
appearance of a bunch of grapes.(221) In many cases, internal
hemorrhoids can be diagnosed confidently on the basis of the
radiographic findings. On occasion, however, large or thrombosed
hemorrhoids can mimic the appearance of tumor, whereas rectal
carcinomas that infiltrate the submucosa can mimic the appearance of hemorrhoids.(221, 223) Digital rectal examination and/
or proctoscopy therefore should be performed whenever the
radiographic findings are equivocal.
Technical errors occur due to poor bowel preparation and
adherent stool can be difficult or impossible to differentiate from
true polypoid lesions. Regimens to prepare the colon are similar
to CTC and OC. Scout images are taken before the study and if
stool is seen in the colon a rescheduled barium enema examination may be performed after more rigorous bowel preparation.
DCBE are a fairly safe procedure, but the referring physician
should state if a recent endoscopic intervention has been performed. There should be a 1-week interval between barium enema
examination and performance of large-forceps biopsy through a
rigid sigmoidoscope, snare polypectomy, or hot biopsy; because
these endoscopic interventions may tear the colonic mucosa and
result in a small risk of perforation. Performance of a smallforceps biopsy through a flexible sigmoidoscope or colonoscope
does not preclude performance of barium enema examination on
the same day.(224, 225)
DCBE has been exhaustively reviewed, usually retrospectively.
DCBE has a sensitivity of 70% for polyps >7 mm (226–229) and
a sensitivity of 81–95% in detecting polyps >1 cm in diameter
(226–228). The detection rate for colorectal cancer or malignant
stricture ranges from 70% to >96% (230–232). The American
Cancer Society guideline for colorectal cancer screening includes
DCBE examinations at 5- or 10-year intervals for patients with
average risk and older than 50 years of age.(233) In conclusion,
DCBE can be used to detect most polyps (>10 mm) that are at
11
improved outcomes in colon and rectal surgery
Figure 11.41 Ulcerative Colitis Late in the Disease. DCBE demonstrates blunting
of the haustral markings with a narrow tubular appearance of the sigmoid colon,
referred to as a “lead pipe colon”.
Table 11.8 Small Bowel Studies.
Examination Technique Benefits and Limitations
Small Bowel Follow
Through (SBFT)
Small Bowel
Enteroclysis
Patient drinks barium
while a series of
supine abdominal
films are obtained
until the terminal
ileum and cecum are
filled.
This study provides more
uniform distension
of the bowel, even
distribution of
barium, superior
anatomic detail,
and shorter overall
examination time.
Demonstrates the
mucosal surface, but
is insensitive; and
limited by overlap
of bowel loops, poor
distension, and
intermittent filling.
risk for malignant degeneration and provides an invaluable public service by helping to lower the mortality rate due to colorectal
cancer.(234)
Ulcerative Colitis
Barium enema can be used to confirm the diagnosis of UC, to differentiate it from Crohn’s disease/colitis, and to assess the extent
and severity of disease. The radiographic appearance of UC
depends on the state of the disease process.(216) Early in the disease, the mucosa is stippled with barium adhering to the confluent, superficial ulcers. Collar button ulcers are deeper ulcerations
of thickened edematous mucosa with crypt abscesses extending
Figure 11.42 Crohn’s Disease “String Sign”. Small bowel follow through
demonstrates fibrosis and progressive thickening of the bowel wall that narrows
the terminal ileum, producing the “string sign”.
in the submucosa. As the ulcerations enlarge, inflammatory psuedopolyps (islands of residual mucosa) and inflammatory polyps
(islands of inflamed mucosa) appear as irregular projections into
the bowel lumen. Late in the disease (Figure 11.41), there is blunting of the haustral markings with a narrow tubular appearance to
the colon, referred to as a “lead pipe colon”.(216) The terminal
ileum is usually normal, but rare backwash ileitis may produce an
ulcerated and patulous terminal ileum. Barium contrast studies
are not able to distinguish UC associated polyps from adenomatous polyps or dysplasia; and UC associated cancers tend to be
flat or infiltrating and do not always appear as typical neoplasms.
Therefore, contrast enemas are not recommended for routine
surveillance.(216)
Crohn’s Disease and Crohn’s Colitis
The appearance of Crohn’s disease in the small bowel and the
colon is similar (Table 11.8). Shallow, 1 to 2 mm depressions usually surrounded by a well-defined halo, called aphthous ulcerations, are the earliest mucosal lesions seen in Crohn’s disease.
(235) Other hallmarks are: (1) thickened and distorted folds; (2)
fibrosis with thickened walls, contractures, and stenosis (Table
11.3). Fibrosis and progressive thickening of the bowel wall
narrow the lumen producing the “string sign” in the terminal
ileum (Figure 11.42). Pseudodiverticula of the colon are formed
by symmetric fibrosis on one side of the lumen, causing saccular outpouchings on the other side. Deep ulcerations are larger
and often linear, forming fissures between nodules of elevated
11
limitations of colorectal imaging studies
Figure 11.43 Divertivulitis. Barium enema demonstrates a deformed colon wall
with diverticular sacs.
edematous mucosa (“cobblestone pattern”). Contrast enemas are
better than colonoscopy at identifying and characterizing fistulas,
strictures, and the distribution of disease.(236)
Diverticulosis and Diverticulitis
Diverticula are often seen on barium enema examinations, as
barium or gas-filled sacs outside the colon lumen. Barium enema
examination is considered safe for diverticulitis, except when
signs of free intraperitoneal perforation or sepsis are present.
Diverticulitis appears as deformation of the colon wall in association with diverticular sacs (Figure 11.43), and occasionally
extravasation of barium outside the colon lumen. Abscess can
cause extrinsic mass effect on the adjacent colon and barium
can leak into the abscess cavities. A colovesical fistula is the most
common diverticular associated fistula, but contrast enemas are
able to make the diagnosis only 20% of the time.(237)
Colonic Lymphoma, Submucosal, and Extracolonic Lesions
Lymphoma can appear as small or large nodules, which may
ulcerate and perforate. Diffuse infiltration of the bowel wall
results in bulbous folds and thickened bowel wall. In contrast
to primary colorectal cancer, narrowing of the lumen is uncommon, and dilation occurs when transmural disease destroys
innervations.
Endometriosis commonly implants on the sigmoid colon and
rectum.(238) Defects are frequently multiple and of variable
size. Barium studies demonstrate sharply defined defects that
compress, but do not usually encircle the lumen. Benign pelvic
masses such as ovarian cysts, cystadenomas, teratomas, and uterine fibroids produce smooth extrinsic mass impressions on the
colonic wall, which is displaced but not invaded. Malignant pelvic tumors and metastases involved with the colon often cannot
be differentiated from primary tumors by imaging methods, and
Figure 11.44 Cecal Volvulus. Water soluble contrast enema demonstrates a
beak like termination at the point of obstruction in the ascending colon with a
markedly dilated cecum seen high in the abdomen.
Crohn’s disease may look similar. Lipomas appear as a smooth,
well-defined, round filling defect, usually 1 to 3 cm in diameter.
The tumors are soft and change shape with compression.(239)
(CT can confirm. See CT scan: other tumors of the colon).
Water-Soluble Contrast Enema
Volvulus and Intussusception
Sigmoid volvulus appears as obstruction that tapers to a beak at
the point of the twist, usually approximately 15 cm above the anal
verge. Mucosal folds spiral into the beak at the point of obstruction. Cecal volvulus appears as a beak like or twisted termination
at the point of obstruction in the ascending colon with a dilated
cecum high in the abdomen (Figure 11.44).
Ileocoloc and colocolic intussusception on contrast studies
demonstrate barium trapped between the intussusceptum and
the receiving bowel, forming a coiled-spring appearance.
Postoperative Complications and Anastomotic Assessment
Water-soluble contrast enemas are frequently used postoperatively to examine a colocolic, colorectal, coloanal, or ileal—
anal anstomosis.(240) The studies are performed by retrograde
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improved outcomes in colon and rectal surgery
Figure 11.45 Anastomotic Leak. Water soluble contrast enema shows extravasation
of contrast into the presacral space.
Figure 11.47 Normal Defecogram. Lateral radiograph is obtained with the
patient in a neutral position after a thick barium paste is placed into rectum.
Figure 11.46 Anastomotic stricture. Small bowel follow through and water
soluble contrast enema demonstrate an ileal pouch–anal anastomotic stricture.
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Figure 11.48 Anorectal Angle. The anorectal angle is created by the intersection of the
long axis of the anal canal and a line drawn along the posterior wall of the rectum.
limitations of colorectal imaging studies
administration of a water-soluble contrast under the weight of
gravity or by direct hand injection via a catheter inserted into the
anal canal. Radiographic findings of an anastomotic leak include
the extravasation of contrast freely into the peritoneal cavity or
into a contained cavity (Figure 11.45). Water-soluble contrast
enema is more sensitive than CT with rectal contrast.(240) Total
proctocolectomy and ileal pouch—anal anastomosis (Figure
11.46) complications include anastomotic stricture.(241–244)
Some studies have cited an anastomotic diameter of 8 mm or less
as the threshold value for diagnosing strictures that may need
dilatation procedures before ileostomy closure.(245)
Physiologic Examinations
Chronic constipation and incontinence are common complaints
with many possible etiologies. Multiple examinations are available to assess the physiology of the lower GI tract, including
defecography, anorectal manometry, balloon proctography, and
colon transit studies.
Defecography
Defecography (evacuation proctography) is a dynamic evaluation of the anatomy and mechanics of defecation. A thick barium paste is deposited within the rectum. Static lateral images
are obtained with the patient in a neutral, anal contraction, and
straining position. Fluoroscopic video is then obtained during
the act of defecation. The static images allow measurement of the
anorectal angle, the angle created by the anal canal, and posterior
wall of the rectum (246) (Figure 11.47 and 11.48). As the patient
defecates, the anorectal angle should straighten and approach
180 degrees. Abnormally high or low anorectal angles suggest a
mechanical cause for the patient’s constipation. The length that
the anorectal junction descends during defecation can be measured as well. An abnormal length of descent (>5 cm) of the anorectal junction can be a source of pudendal nerve damage and,
if chronic, incontinence.(247) The most common abnormality detected by defecogram is a rectocele. A rectocele is an outpouching of the rectum, usually along the anterior wall. Retained
barium in the rectocele can document incomplete rectal evacuation. In severe cases of rectoceles, internal rectal prolapse can be
observed by defecogram. A negative defecogram can exclude such
conditions as enteroceles, sigmoidoceles, rectal prolapse, rectal
intussusception, puborectalis muscle dysfunction, and posterolateral pouches.
throughout the colon. A functional outlet obstruction, such as
rectal prolapsed or anismus, is suggested if there is delayed transit
time with clustering of the radiopaque markers in the rectosigmoid colon.(246)
Anorectal Manometry and Balloon Proctography
Anorectal manometry is performed to assess rectal sensation and
motor function. The rectum is distended by a balloon. The normal response to rectal distention is contraction of the external
anal sphincter and relaxation of the internal anal sphincter. Loss
of this reflex can be detected by anorectal manometry and can
be seen in Hirschsprung’s disease or severe idiopathic constipation.(249) Balloon proctography is a similar examination where
the rectal balloon is filled with a contrast material, allowing visualization of the rectum. Visual assessment of the rectum with
calculation of the anorectal angle can be performed in addition
to measurement of the anorectal pressure.(248) Some studies
suggest that balloon proctography is less sensitive than defecography in detecting certain anatomic abnormalities, including
rectoceles.
ULTRASONOGRAPHY (US)
Transabdominal Ultrasound and Intraoperative
Ultrasound (IUS)
Ultrasonography (US) utilizes sound waves to provide real time
imaging of the body. A transducer is placed on the patient that
not only generates sound waves (of a single frequency) but also
detects the reflected echoes. US can successfully image solid
visceral organs and fluid filled structures. US is superb at differentiating between cystic and solid structures, and is frequently
Colorectal Transit
Colorectal transit times can be documented by having the patient
ingest a barium meal and obtaining serial abdominal radiographs. All the barium should be cleared in a normal patient in
4 days. Retained barium after 4 days confirms delayed colorectal transit time.(248) An alternative method utilizes radiopaque
rings (Sitzmarkers®, Konsyl Pharmaceuticals, Ft Worth, TX) to
assess colonic transit time. Twenty four markers are ingested. The
patient is instructed not to use enemas, laxatives, or suppositories for 5 days. Radiographs are obtained daily or on days 1, 3,
and 5.(249) Eighty percent of the markers should pass in 5 days
and all of the markers normally pass by the seventh day.(246,
248) The diagnosis of colonic hypomotility/inertia is suggested if
there is delayed transit time and the markers are scattered evenly
Figure 11.49 Appendicitis. Axial view of the appendix reveals a thickened and
hypoechoic wall. An appendicolith is represented by the hyperechoic material
seen within the lumen (arrow).
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