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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_1499_Библиотеки_им_академика_М_И_Перельмана.pdf
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Incontinence: loss of contrast before adequate completion of test.
Negative diagnostic impact of noncooperative patient.
Specific Test: Conventional Defecating Proctogram (Defecography)
PURPOSE
As stated above: technique relatively simple, cheap, unlimited length of sequence.
EQUIPMENT AND TECHNIQUE
Instillation of radiographic contrast paste; patient then positioned on radiotransparent Brunswick chair sequence of resting,
squeezing, straining, evacuation.
Imaging: fluoroscopy with static images or preferably video defecography.
RISKS
Radiation exposure: 450–700 mrem (4.5–7.0 mSv).
INTERPRETATION
Pathology of primary relevance: quality of dynamic changes, transition, effective evacuation, pelvic floor descent (below
pubococcygeal line), puborectalis relaxation vs paradoxical contraction, rectocele, intussusception, prolapse, enterocele,
incomplete evacuation.
Pathology of minor relevance: absolute values for anorectal angle (high inter-observer variability!).
PITFALLS
False negative: presence of significant fecal incontinence results in loss of contrast without adequate expansion of rectal
reservoir.
Prevalence of "pathologic" findings in asymptomatic patients: eg, rectocele ~25–50%.
Overinterpretation of findings: rectocele, angle, mucosal folds
always clinical correlation needed to determine whether the
documented findings are truly relevant for the patient's complaints.
Specific Test: MRI Defecography
PURPOSE
If available, MRI is the preferred technique as both endoluminal and extraluminal events are visible during whole course of
evacuation. In contrast to "dynamic MRI" (in supine patient), open interventional MRI defecography examines patient in the
more relevant sitting position and during the actual evacuation process.
EQUIPMENT AND TECHNIQUE
Requires very expensive infrastructure and equipment: superconducting open-configuration MRI system: allows patient to sit
within. Instillation of MRI-opaque contrast paste (gadolinium 2.5 mmol/L): 300 mL of synthetic stool (mashed potato starch)
mixed with 1.5 mL of gadopentetate dimeglumine (377 mg/mL). Patient positioned on MRI-transparent chair in center of
open-configuration MRI. MRI image sequence of resting, squeezing, straining, evacuation (with static images or preferably
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video defecography).
RISKS
MRI related (contraindications: magnetic implants, etc), gadolinium side effects.
INTERPRETATION
Pathology of primary relevance: quality of dynamic changes including assessment of other pelvic and abdominal organs:
transition, effective evacuation, pelvic floor descent (below pubococcygeal line), pelvic organ and rectal prolapse, enterocele,
puborectalis relaxation vs paradoxical contraction, rectocele, intussusception, incomplete evacuation.
Pathology of minor relevance: absolute values for anorectal angle (high inter-observer variability!).
PITFALLS
Limited availability of infrastructure.
Other pitfalls: as above.
Further Steps
Depending on clinical circumstances and radiologic findings:
Anophysiology studies.
Contrast enema.
Dynamic MRI.
Cross-Reference
Anophysiology studies (Ch. 2)
Colonic transit study (Sitzmark) (Ch. 2)
Pelvic floor dysfunction (618.X) (Ch. 4)
Functional disorders—chronic constipation (564.0X) (Ch. 4)
Functional disorders—irritable bowel syndrome (IBS, 564.1) (Ch. 4)
Selected colorectal reference values (App. 2)
COMPUTED TOMOGRAPHY (CT SCAN)
Overview
Cross-sectional imaging studies (CT, MRI, ultrasound) have become a cornerstone of modern medicine. All specialties
(including surgery, oncology) rely on a noninvasive and reproducible evaluation. Computed tomography (CT scan) is by far
the most universal and fastest tool to evaluate and quantitate tumor burden and infections, to plan surgical resection, to
perform precise interventions, to detect comorbidities.
Increased resolution and slice thickness allows complete reconstruction and evaluation in different planes and to filter areas
of interest. Ability to read CT scans is mandatory for colorectal surgery.
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Alternatives
MRI.
Abdominal ultrasound.
Surgical exploration.
Indications
Cancer staging: local extent (particularly for rectal cancer), secondary pathology (evidence of perforation/obstruction,
liver metastases, hydronephrosis, paraaortic lymph node involvement, etc).
Assessment of cancer response or progression (during neo-/adjuvant treatment)
Evaluation of infections, sepsis, peritonitis, respiratory dysfunction, postoperative complications, etc.
Detection of coexistent pathology: liver cirrhosis, ascites, anatomic variants, inflammatory changes, gallstones,
kidney stones.
Evaluation of unexplained abdominopelvic symptoms: pain, distention, abdominal wall hernia (Figure 2–7), etc.
CT colonography and CT enterography (see respective sections later in this chapter).
Helical CT scan: workup of active GI bleeding; vascular extravasation of contrast?
Figure 2–7.
CT scan showing large incisional hernia.
Advantages
Universal availability.
High sensitivity and specificity for detecting liver lesions > 1 cm (90% and 95%).
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Not examiner-dependent, more reproducible than ultrasound.
Risks and Limitations
Risks: radiation exposure (2000 mrem [20.0 mSv]), contrast allergy.
Adequate imaging requires administration of oral and IV contrast: not possible in renal insufficiency and contrast
allergies.
Correlation with other evidence needed.
Distinction between benign and malignant lesions frequently is not possible.
Characteristic Features
Cancer: visible mass (primary colon tumor not necessarily visible on CT), evidence for metastatic spread, invasion of
other structures, critical proximities, etc.
Peritonitis/abdominal crisis: abscess formation (pelvic, pericolonic, subhepatic, subphrenic, interloop, etc), evidence
of contrast extravasation (leak, perforation), extraluminal air?
Diverticulitis: important for staging/possible intervention: phlegmon, wall thickening, fat stranding, abscess formation
(pericolonic, pelvic), confined extracolonic air, free air, ascites.
Appendicitis: increased diameter (> 6 mm), fecalith? Perifocal inflammatory changes (fluid, stranding, limited wall
thickening, free fluid.
IBD:
– Crohn disease: bowel wall thickening, skip areas, fat stranding, abscess formation, fistulas (short-cut of oral
contrast, air in bladder), lymphadenopathy.
– Ulcerative colitis: typically no specific pathology on CT, occasionally marked enhancement of mucosa.
Colitis: marked enhancement of mucosa, possible colonic wall thickening (eg, C difficile colitis), thumbprinting
(mucosal edema).
Ischemic colitis: altered enhancement of bowel wall (increased/decreased), pericolonic stranding, incomplete course
of visceral blood supply, pneumatosis (air in bowel wall: suggestive of necrosis), portal vein gas (from gangrenous
process), free air.
Bowel obstruction: air/stool distribution, transition point, colonic wall thickening, evidence of causative pathology
(tumor, adhesion), signs of perforation, cecal diameter (> 12 cm?), transverse colon diameter (> 6 cm?),
pneumatosis?
Active GI bleeding: vascular extravasation of contrast, contrast enhancement of bowel wall, thickened bowel wall,
vascular dilations.
Cross-Reference
Magnetic resonance imaging (MRI) (Ch. 2)
Colorectal cancer—colon cancer (153.X) (Ch. 4)
Ischemic colitis (557.X) (Ch. 4)
Diverticular disease (diverticulosis, diverticulitis, 562.1X) (Ch. 4)
Complications—leak (997.4) (Ch. 4)
CT COLONOGRAPHY ("VIRTUAL COLONOSCOPY")
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Overview
Noninvasive imaging of entire colon by means of high-resolution CT scan with digital 3D-reconstruction of colon, allowing for
a virtual fly-through (Figure 2–8). In addition visualization of extracolonic structures. Test still requires full bowel cleansing,
which is biggest hurdle to wide screening. During procedure: rectum is pumped with air, which causes significant discomfort
and rarely perforation.
Figure 2–8.
CT colonography showing colonic mass.
Data somewhat divergent: some studies showing similar sensitivity as standard colonoscopy (> 90% for polyps > 8 mm),
others showing only moderate sensitivity/specificity and high inter-observer variability. Therefore CT colonography promising,
but not yet "prime time" test.
Future: rapid technologic progress is expected, leading to better resolution, better distinction between stool and pathology,
and no need for bowel prep.
Alternatives
Colonoscopy.
Barium-air contrast enema.
Indications
Failed colonoscopy.
Primary screening (not yet recommended).
Advantages
Fast (10–15 minutes), avoidance of instrumentation, overall safe.
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Sedation not required patients are not dependent on other people (eg, driving).
Better patient acceptance.
Detection of significant extracolonic pathology: aortic aneurysms, renal cell carcinomas, etc.
Risks and Limitations
Risks: risk of perforation low but not zero, radiation exposure (> 2000 mrem [20.0 mSv]).
Abnormal findings
further testing with colonoscopy needed.
Frequent unnecessary evaluations/surgeries for incidental findings.
Need for bowel prep (like colonoscopy).
Insufflation of air through rectal tube associated with cramping: more uncomfortable than standard colonoscopy (as no
sedation given).
May not be covered by insurance for screening (unless colonoscopy failed).
Characteristic Features
Colonic: polyps, mass, stricture, diverticulosis, colonic road map.
Extracolonic: mass (kidney, adrenals, pancreas, etc), gallstones, vascular abnormalities, etc.
Cross-Reference
Colorectal cancer screening/surveillance (Ch. 2)
Colonoscopy (Ch. 2)
Contrast enemas (Ch. 2)
Polyps (211.3) (Ch. 4)
Polyposis syndromes (211.3, 235.2) (Ch. 4)
Colorectal cancer—colon cancer (153.X) (Ch. 4)
Bowel preparation/cleansing (Ch. 7)
CT ENTEROGRAPHY ("VIRTUAL SMALL BOWEL FOLLOW-THROUGH")
Overview
Noninvasive imaging of the small bowel by means of high-resolution CT scan with improved spatial and temporal resolution
to allow digital 3D-reconstruction of small intestine. The technique involves administration of large volume oral contrast (to
achieve bowel distention) in conjunction with IV contrast to enhance the mucosa.
Future: rapid technologic progress is expected with better resolution, fly-through.
Alternatives
Small bowel follow-through.
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Capsule endoscopy.
Indications
Crohn disease.
Enterocutaneous fistula.
Partial/intermittent small bowel obstruction.
GI bleeding of unknown source.
Advantages
Fast (10–15 minutes), noninvasive, safe.
Accurate visualization of extent/distribution of disease, separation of intestinal overlay projections, demonstration of
extraluminal pathology.
Risks and Limitations
Risks: radiation exposure (2000 mrem [20.0 mSv]).
Relatively new modality: not universally available, still in learning curve.
Contraindicated in: contrast allergy, renal insufficiency.
Characteristic Features
Crohn disease: small bowel inflammation with increased wall enhancement, thickening, inflammatory mass, presence
and number of strictures, enlarged vessels, perienteric inflammatory changes and abscess, presence/characterization
or absence of fistula.
Enterocutaneous fistula: characterization of fistula-bearing bowel segment, identification of distal obstruction,
assessment of extraluminal scar tissue.
Bowel obstruction: evidence and nature of transition point, additional distal obstructive sites.
GI bleeding of unknown source: identification of altered bowel segment, inflammatory signs, tumor.
Cross-Reference
Small bowel obstruction (SBO) (Ch. 1)
Small bowel follow-through (SBFT) (Ch. 2)
IBD—Crohn disease (555.X) (Ch. 4)
Enterocutaneous fistula (569.81) (Ch. 4)
MAGNETIC RESONANCE IMAGING (MRI)
Overview
MRI—like other cross-sectional imaging studies (CT, ultrasound)—provides reproducible high-resolution imaging, but with the
advantage of being examiner-independent and avoiding radiation exposure. MRI is based on detection and mapping of radio
signals emitted by alignment of spins of hydrogen atoms that are exposed to strong magnet fields and stimulated by radio
waves. The different hydrogen (ie, water) content of tissues allows creation of anatomic images.
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T1: realignment of nuclear spins with magnetic field T1-weighted images show fluid black, fat white; contrast
improvement with gadolinium-enhancement (ie, vascularity) and fat suppression: abdominal MRI.
T2: dephasing of nuclear spins with transverse field T2-weighted images show fluid white, fat dark; pelvic MRI.
MRI and CT scan are exchangeable to some degree but complementary for specific areas. MRI typically has an advantage in
distinguishing soft tissue structures and processes with different water content, eg, inflammatory or neoplastic processes,
muscular and fascial anatomy, etc.
Increased contrast and resolution in dynamic protocols allow noninvasive reconstruction and visualization of vascularization
(MRI angiogram), duct structures (eg, MRCP), pelvic floor dynamic during straining-squeezing sequences and defecation (MRI
defecography).
Alternatives
CT scan.
Abdominal ultrasound.
Surgical exploration.
Indications
Cancer staging: local extent, radial margin of rectal cancer.
Discrimination between liver cysts, metastases, hemangiomas.
Evaluation of abdominal wall pathology.
MRCP: noninvasive ERCP for evaluation of biliary disease, cholestasis.
MRI angiography: noninvasive angiogram.
Pelvic MRI with dynamic sequences: pelvic organ prolapse syndrome, MRI defecography.
Anorectal pathology, MRI fistulography.
Advantages
No radiation exposure.
Better resolution for soft-tissue pathology.
Not examiner-dependent, more reproducible than ultrasound.
Risks and Limitations
Contraindications: pacemaker, metallic implants, patient claustrophobia.
Adequate imaging may require administration IV gadolinium.
Correlation with other evidence is needed.
Distinction between benign and malignant lesions is not always possible.
Nonradiologists are still less familiar with MRI than with CT images.
Characteristic Features
Tumor: T2-weighted intense (white); T1-weighted dark, early enhancement with gadolinium.
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Scar tissue: T1- and T2-weighted low signal intensity, no gadolinium enhancement.
Inflammation: T2-weighted intense (white), T1-weighted dark, delayed enhancement with gadolinium.
Dynamic pelvic MRI: lubricant gel used as rectal and vaginal contrast; dynamic evaluation during rest, squeeze,
strain, evacuation: assessment for perineal descent, rectocele, cystocele, vaginal prolapse, enterocele (comparison to
pubococcygeal line).
Cross-Reference
Defecating proctogram (defecography) (Ch. 2)
Computed tomography (CT scan) (Ch. 2)
Angiography with possible embolization (Ch. 2)
Perianal/-rectal fistula (565.1) (Ch. 4)
Colorectal cancer—colon cancer (153.X) (Ch. 4)
Ischemic colitis (557.X) (Ch. 4)
Diverticular disease (diverticulosis, diverticulitis, 562.1X) (Ch. 4)
Pelvic floor dysfunction (618.X) (Ch. 4)
POSITRON EMISSION TOMOGRAPHY (PET/PET-CT)
Overview
Positron emission tomography—either alone or in conjunction with CT—provides imaging based on metabolic tissue activity.
PET substrate is an 18F-glucose analogue that is taken up into the cell but cannot be further metabolized and therefore
accumulates intracellularly. Imaging with a whole body scanner allows for identification of foci with increased metabolism. Of
particular interest are tumors, which are generally metabolically more active than normal tissue as they take up and burn
large amount of glucose.
Expected Benefits
Detection of previously unidentified tumor foci.
Qualitative differentiation between scar tissue and tumor recurrence or metastases.
Limitations
Generally unspecific, potentially altered/suppressed by chemotherapy. False positive activity possible in GI mucosa ( repeat
study).
Test Element: Whole Body PET
PURPOSE
1. Differentiation of local recurrence from unspecific scar tissue.
2. Detection of distant metastasis, eg, before deciding on surgical management of proven local recurrence.
EQUIPMENT AND TECHNIQUE
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PET scanner. 18F-fluoro-deoxyglucose (FDG).
RISKS
Minimal radiation exposure: 14–20 mrem (0.14–0.2 mSv).
PITFALLS
Distinction between neoplastic and inflammatory changes not sufficiently reliable.
False negative: tumor suppression during concomitant chemotherapy, tumors without significant FDG uptake; false positive:
GI mucosa.
INTERPRETATION
Areas of normally increased activity: bladder, brain, occasionally GI mucosa.
Tumor generally more active than scar tissue.
Test Element: PET/CT
PURPOSE
Improved diagnostic accuracy through combination of the activity assessment (PET) with imaging (CT) to directly correlate
hypermetabolic areas with the respective morphology.
EQUIPMENT AND TECHNIQUE
PET and CT scanner. 18F-FDG.
RISKS
Significantly higher radiation exposure than PET alone: 2000–2500 mrem (20–25 mSv).
PITFALLS
As above.
INTERPRETATION
Independent analysis of PET and CT and overlap correlation of areas with increased metabolic activity to morphologic
changes on CT.
Further Steps
Other imaging modalities.
CT-guided or open biopsy of suspicious areas vs surgical exploration.
Watchful waiting with repeat exams to assess temporal change.
Cross-Reference
Computed tomography (CT scan) (Ch. 2)
Magnetic resonance imaging (MRI) (Ch. 2)