Improved Outcomes in Colon and Rectal Surgery part 14 pptx

11 improved outcomes in colon and rectal surgery called to do so. The US beam will be completely reflected by bone and sufficiently scattered by air to thwart imaging distal to these substances. When the transmitted sound wave reflects off a moving target, the returning echo will have a slightly different frequency (the Doppler Effect). Doppler US capitalizes on this principle and allows the determination of direction and veloc- ity of a mobile target.(250) The most frequent application for Doppler US is the detection and quantification of blood flow. Specifically, Doppler US is extremely helpful in evaluating the upper and lower extremities for deep venous thrombosis. US has many advantages. It is an inexpensive, widely available modality that provides real time, multiplanar images with no radiation exposure to the patient. The US equipment is mobile, allowing critically ill patients to be imaged within the ICU. The structures that can be studied by US include arteries, veins, liver, spleen, gallbladder, bile ducts, pancreas, kidneys, bladder, uterus, and ovaries. Transabdominal US is typically limited in its evaluation of the gastrointestinal tract. Intraluminal bowel gas will obscure the surrounding anatomy. Therefore, patients should be NPO for 4 to 8 hours before being imaged to reduce the volume of intraluminal gas.(251) Nonetheless, US can detect abnormal loops of bowel. Wall thickening, hyperemia, fecoliths, bowel dis- tention, wall edema, and noncompressibility all can be detected by ultrasound and suggest intestinal pathology. US can be helpful in diagnosing a wide variety of disease processes including appendicitis (Figure 11.49), intussusception, inflammatory bowel disease, colitis (from numerous causes), and neoplasm (Figure 11.50). Due to the superior sensitivity and specificity of other imaging modalities, US evaluation of the bowel is typically reserved for situations where limitation of radiation exposure is desired (i.e., pediatric and pregnant patients). Figure 11.50 Colon Cancer Liver Metastasis. US of the liver demonstrates an isoechoic mass with a hypoechoic peripheral halo. This “target” appearance can be seen in a variety of disease processes but is a common finding in metastatic colon cancer and hepatocellular carcinoma. Figure 11.51 Normal Layers of Colon on Intrarectal ultrasound (Graphic representation of 5 layers). Figure 11.52 Normal Endoluminal Ultrasound. Figure 11.53 Ultrasound of uT3 rectal mass. 11 limitations of colorectal imaging studies Intraoperative ultrasound (IUS) can provide important information to the surgeon and is commonly used to evaluate the liver for metastatic disease and guide the subsequent metastasectomy. IUS is particularly useful in delineating the relationship between hepatic tumors and adjacent vasculature.(252) Studies have shown that IUS provides vital information to the surgeon during the procedure that will affect surgical decision making in up to 38% hepatic metastasectomy.(251) Endoluminal Ultrasound Endoluminal ultrasound’s (EUS) impact on the workup for colorectal cancer continues to expand. Transrectal US appears to be the most accurate imaging modality in determining the extent of local invasion of rectal cancer.(253) EUS can delineate the components of the intestinal wall. Images typically consist of five rings of different echogenicity (3 hyperechoic and 2 hypoechoic) that allow the localization of the mucosa, muscularis mucosa, submusoca, muscularis propria, and serosa (254)) (Figure 11.51). Colorectal tumors will appear as a hypoechoic mass that distorts the normal bowel architecture (Figure 11.52 and 11.53). EUS can accurately identify the specific layers of the bowel wall invasion, thereby elucidating the tumor stage.(255) Recent studies have shown that transrectal US has difficulty differentiating between tumor and peritumoral inflammation, thereby producing a ten- dency to over stage a recently diagnosed cancer. EUS is often used in conjunction with traditional endoscopy to allow direct visualization of the mucosa, assess the depth of wall involvement, facili- tate biopsy, and evaluate for pericolonic lymphadenopathy. While EUS has the ability to detect local lymph node involvement, cross sectional imaging (CT, MRI, or PET) is still needed to evaluate for regional and distant metastatic disease.(255) Nononcologic applications of EUS include the evaluation of the colon, rectum, and anus for strictures, fistulas, and abscesses. Transanal US is often used in the evaluation of incontinence as it can detect defects within the internal anal sphincter, external anal sphincter, puborectalis sling, and pelvic musculature.(254) magnetic resonance imaging (mri) In magnetic resonance imaging, strong magnetic fields and tar- geted radiofrequency pulses are harnessed to map the location of protons within the body. Depending on the specific imaging parameters utilized, protons within fat (T1 MRI sequences), or water (T2 MRI sequences) can be selectively displayed. Ionizing radiation and iodinated contrast agents are not used. MRI images are degraded by motion and the combination of bowel peristalsis and diaphragmatic movement has traditionally limited the application of MRI in the evaluation of gastrointestinal pathology. (254) Ferromagnetic metals cannot be taken into the magnetic field and therefore most surgical implanted devices have been transitioned to MRI compatible materials. Care must still be taken with certain implanted devices as the strong magnetic field may cause malfunction. Confirmation of MRI compatibility with the manufacturer is required for implanted devices such as car- diac pacemakers, cochlear implants, spinal cord stimulators, and basal ganglion stimulation devices. Nephrogenic systemic fibrosis (NSF) is a disorder seen exclusively in patients with chronic renal insufficiency that presents with diffuse systemic sclerosis with particularly severe cutaneous fibrosis. In 1997, NSF was linked to gadolinium exposure in patients with renal insufficiency. The FDA has recently placed a black box warning on gadolinium containing MRI contrast agents.(256) Technological advancement with quicker image acquisition has reduced motion blurring and has allowed the diagnostic assessment of the sigmoid colon and rectum (anatomically fixed structures). (257) While MRI can be useful in the diagnosis of inflammation of the GI tract (for example, appendicitis, Crohn’s disease, and ulcerative colitis) (Figure 11.54), the largest advances have been made in evaluation of colorectal cancer.(254) The effectiveness of MRI is similar to CT for the initial staging of colorectal tumors.(258) MRI is very accurate evaluating the pelvis for local rectal tumor Figure 11.54 A and 11.54B Terminal Ileitis in Crohn’s Disease. Axial (A) and coronal (B) T1-fat saturated MRI images demonstrate mucosal enhancement within the terminal ileum (arrow) with no enhancement in the adjacent normal ileum (arrow head). The mucosal enhancement indicates active terminal ileitis. (a) (b) 1 improved outcomes in colon and rectal surgery extension (Figure 11.55), and has an advantage over CT in the evaluation of tumoral invasion of the levator ani, mesorectal fascia, internal and external sphincter muscles.(258–259) Endorectal MRI is a promising new technique that can help evaluate the depth of local tumor invasion. Endorectal ultrasound has been shown to be equally sensitive and specific as our currently available endorectal MRI and can be performed in a fraction of the time.(258, 260) MRI is also a valuable tool in detecting distant metastatic disease. Metastatic foci within the brain, skeleton, and liver are readily detected with MRI. Local tumor recurrence can be dif- ferentiated from mature fibrosis if the surgical resection was at least 1 year prior. Unfortunately, immature fibrosis (<1 year old) cannot be successfully distinguished from recurrent tumor with MRI.(258, 259) nucLear medicine imaging Positron Emission Tomography Positron Emission Tomography (PET) has been approved by Medicare for the diagnosis, staging, and restaging of colorectal cancer since 2001.(261) Unlike other imaging modalities that rely on architectural distortion, PET scans detect neoplasm based on physiologic differences between normal tissue and cancer cells. Malignant cells have a higher baseline metabolic state, increased mitotic activity, and consume more glucose. PET scans utilize the glucose analog F-18 fluorodeoxyglucose (F-18 FDG). F-18 FDG is transported into the cell through transmembrane glucose transporters but, unlike glucose, it does not undergo further metabolism.(261, 262) This causes an accumulation of F-18 FDG within the tumor cell. Fluorine-18 emits positrons that subsequently undergo annihilation when contacted by electrons. This annihilation produces gamma photons that are summated by specialized detectors and allow image generation. The photon count and inferred amount of glucose uptake is reported in standard uptake values (SUVs). The SUV takes into consideration the dose of F-18 FDG injected and body surface Figure 11.55 Perirectal Mass. Fluid sensitive (STIR) T2 MRI of the pelvis shows a hyperintense mass adjacent to the rectum, worrisome for rectal carcinoma. However, after resection, this mass was found to be a high grade liposarcoma. (a) (b) Figure 11.56 A–11.56C Comparison between CT and PET. Figure 11.56A demonstrates multiple discrete areas of hypermetabolism within the liver on PET scan, representing metastatic colon adenocarcinoma. Figure 11.56B shows a noncontrast CT scan of the same patient. The multiple metastatic foci are nearly impossible to detect without contrast. Figure 11.56C. Iodinated contrast helps to delineate between normal hepatic tissue and hypodense metastatic disease. (c) 11 limitations of colorectal imaging studies area.(261) In general, a SUV value above 2.5 is suspicious for malignancy but may also be secondary to an inflammatory or infectious process.(262) Care must be taken when relying on SUVs as they are only semi-quantitative and many variables affect the reported numeric value. One particularly strong variable is the serum glucose. A high serum glucose level will reduce tumor uptake of F-18 FDG and lower SUV values. Patients typically fast overnight and avoid carbohydrates before the procedure.(262) Blood glucose levels are checked before the examination with a level below 200 mg/dl desired. PET imaging of the colon is very sensitive (>90%) but lacks specificity (40–60%) due to physiologic bowel glucose uptake and hypermetabolic benign lesions, including colitis and benign polyps.(262) The main advantage of PET is its superiority over CT in the detection of metastatic colorectal cancer. PET will detect increased glucose metabolism in regional lymph nodes or distant metastatic sites (Figure 11.56) that do demonstrate enough architectural distortion to be detected as abnormal by CT examination. PET has also been shown to be superior to CT in the evaluation of colorectal cancer recurrence (Figure 11.57) (263). PET can help monitor response to chemotherapy and radiation treatment but does not have the ability to detect microscopic residual disease (262). One of the main limitations of PET is low spatial resolution. This problem has largely been overcome by a new technique that allows the concurrent acquisition of PET and CT images during a single examination. PET/CT augments the localization of malignancy in contiguous or overlapping structures.(262) Differentiation of tumor from infection is problematic when the standard uptake value is only minimally elevated as regional lym- phocytes will metabolize an abundance of F-18 FDG. Likewise, colonic adenomas/polyps can demonstrate hypermetabolism and be misinterpreted as a tumor. Tumors that have a low cell density, small size, or low metabolic activity (including carcinoid and mucinous adenocarcinoma) have a higher likelihood of a false-negative result.(261, 262) Gastrointestinal Scintigraphy Nuclear medicine scintigraphy is a useful tool for the colorectal surgeon. A biologically significant substance (RBC, leukocyte) is labeled with a radioactive isotope that will subsequently emit gamma radiation. These gamma photons are detected by scin- tillation cameras and diagnostic images are generated. Nuclear medicine scintigraphy is especially helpful in answering a specific question. The evaluation for intraabdominal abscess, Meckel’s diverticulum, carcinoid tumor, biliary abnormality, pernicious anemia, and colonic transit time can be performed with radioisotope labeled leukocytes, technetium, octreotide, iminodia- cetic acid, vitamin B12, and diethylene triamine pentaacetic acid (DTPA), respectively.(264) With the expanding use of fused PET-CT imaging, traditional nuclear medicine scintigraphy has a limited role in the management of colorectal neoplasia. In tumors that are known to have high false negative PET rates (i.e., mucinous adenocarcinoma), radioisotope labeled monoclonal antibodies may help in evaluating for occult metastatic disease or recurrence.(264, 265) While multiple monoclonal antibodies have been approved by the FDA, none are currently in widespread clinical use.(266) Tc-99m red blood cell scintigraphy is a frequently utilized examination for the evaluation of lower gastrointestinal bleeding. The patient’s RBCs are labeled with the radioisotope technetium-99m (employing either an in-vivo or in-vitro method) in an attempt to identify red blood cells within the lumen of the GI tract, thereby localizing the source of bleeding. Three criteria are needed to confirm a gastrointestinal bleed. The radiotracer uptake pattern should conform to bowel anatomy, increase in intensity over time, and propagate in an antegrade or retrograde fashion (Figure 11.58). Multiple intraabominal abnormalities, including hepatic hemangiomas, accessory splenic tissue, or colonic angiodysplasia, can simulate a GI bleed but these abnormalities will not change in location over time. A false negative Tc-99m RBC scintigram can be secondary to a slow intestinal bleeding rate or an intermittent bleed.(266) The reported Figure 11.57 PET-CT. PET-CT images show a focal area of hypermetabolic activity in the presacral space, adjacent to the patient’s low anterior resection site for rectal cancer, representing an area of recurrence. Note that this lesion may have been overlooked on the noncontrast CT. 1 improved outcomes in colon and rectal surgery Figure 11.58 A and 11.58B. Lower Gastrointestinal Bleeding. Figure 11.58A shows a single image of a Tc-99m red blood cell scintigram with a GI bleed originating in the transverse colon, near the hepatic flexure. Figure 11.58B is taken 5 minutes later and shows the radiotracer uptake pattern conforming to bowel and moving in an antegrade fashion towards the splenic flexure. (a) (b) sensitivity and specificity of Tc-99m RBC imaging has been reported as high as 93% and 95%, respectively.(264, 266) Tc-99m RBC scintigraphy can detect GI bleeding rates as low as 0.2 cc/ minute (compared to 1.0 cc/minute for traditional angiography), and is a sensitive tool that can help isolate the vascular territory of a bleed and direct percutaneous or surgical intervention.(266, 267) In an unstable patient, a Tc-99m sulfur colloid can be used to detect GI bleeding. Sulfur colloid scintigraphy requires less time for patient preparation and image acquisition but has a lower sensitivity for detecting gastrointestinal bleeding. interVentionaL radioLogy Gastrointestinal (GI) Bleeding The angiographic diagnosis of GI bleeding is based upon visualization of extravasation of contrast into the bowel lumen, and a high rate of bleeding (1 cc/min) is required to visualize extravasation.(268) Angiograms are positive in only about 50% of patients, and a positive Tc-99m RBC scintigraphy scan within the first 5–9 minutes, makes angiography more likely to identify extravasation.(269) The two techniques used for lower GI arterial bleeding are vasopressin infusion and embolization. Vasopressin (pitressin) infused into the proximal SMA or IMA causes both smooth muscle constriction and water retention. Vasopressin can control lower GI bleeding in up to 90% of cases, and half of the patients will never bleed again. Vasopressin requires monitoring in an ICU. Rare complications include car- diac or digital ischemia from vasoconstriction, or hyponatremia from water retention.(268–270) Embolization controls GI bleeding by decreasing the arterial pressure and flow to the point that hemostasis can occur, without creating symptomatic ischemia. Large particles, Gelfoam, or microcoils can be used. Embolization is successful in over 90% of cases, with few instances of bowel ischemia. Rebleeding is reported to occur in 20% of patients. Patients should be moni- tored for bowel ischemia. Delayed ischemic colonic strictures have been reported.(268–270) Percutaneous Abscess Drainage (PAD) Percutaneous abscess drainage (PAD) has played a major role in decreasing the morbidity and mortality associated with surgical Figure 11.59 Percutaneous Abscess Drainage. Axial CT image demonstrates needle placement into the large fluid/air filled abscess. 1 limitations of colorectal imaging studies exploration. CT is the most appropriate modality in image guided PAD (Figure 11.59).(271) PAD of an intraabdominal abscess is effective with a single treatment in 70% of patients and increased to 82% if a second drainage is performed.(272) The overall findings from a large series of 2311 PADs report a success rate of 80–85%.(273) Complication rates of PAD are between none and 10%. Vascular laceration may occur and, if the vessel is small, the bleeding will usually stop spontaneously.(274) Percutaneous abscess drainage may be complicated by bowel perforation from the needle or catheter transversing the bowel. If the patient devel- ops signs of peritonitis after catheter penetration of bowel, then surgical intervention may be required.(275) Image-guided Percutaneous Biopsy The majority of image-guided biopsies can be performed on an outpatient basis. All interventional procedures can result in bleeding, but this complication can be reduced by correction of any coagulopathy before the procedure.(276) US offers the advantage of real-time needle visualization, low cost, portable, and no ionizing radiation (Figure 11.60). US guidance can be problematic in obese patients because the echogenic needle can be hard to visualize in echogenic fat. Lesions located deep to bone or bowel cannot be biopsied with US owing to lack of visualization of the lesion. CT can be used to guide biopsy needles to virtually any area of the body. CT provides excellent visualization of lesions and allows accurate identification of organs between the skin and the lesion.(277) Disadvantages of CT include increased cost, ionizing radiation, and longer procedure times. Complications of abdominal, liver, or lung biopsy include bleeding, introducing infection, pneumothorax, and hemoptysis. Postprocedure pneumothorax may occasionally require chest tube placement and observation in the hospital.(276, 277) Radiofrequency ablation (RFA) and Chemoembolization of Hepatic Metastasis Radiofrequency ablations (RFA) of liver metastasis are performed similar to image-guided needle biopsy, with the RF probe taking the place of the needle. The RF probe is placed in the hepatic tumor and vibrates at a high frequency, conduct- ing heat into and ablating the tumor.(278). Studies show that the overall 5-year survival rate for colorectal liver metastasis treated by RF ablation is similar to surgical series (25–40%). (279) There are no absolute contraindications, and relative contraindications include low platelets and coagulopathy. RFA of hepatic tumors is associated with very low complication rates, generally below 2%. Complications include pain, pleural effu- sion, bleeding, and abscess formation.(278) The treatment of certain tumors (metastatic hepatic lesions) with intravascular delivery of chemotherapeutic agents can be palliative and prolong life, but is not considered curative.(280) A wide variety of chemotherapeutic regimens are used. These chemotherapeutic medications are usually mixed with an embo- lic agent that slows flow and allows the drugs to remain in the organ. Metastatic disease to the liver can also be embolized by Yttrium-loaded microspheres that emit beta-radiation. Fulminant hepatic failure or liver abscess formation occurs in <1% of patients. Gallbladder infarction due to chemoembolization is rare. (280–282) references 1. Bluth EI, Locascio LF Jr, Head SC, Smetherman D. Diagnostic imaging. In Beck DE, ed. Handbook of colorectal surgery. St. Louis: Quality Medical Publishing, 1997: 39–62. 2. Brant WE, Helms CA. Fundamentals of Diagnostic Radiology, 3rd ed, Vol III. 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AJR Am J Roentgenol 2000; 174: 901–13. . enhancement indicates active terminal ileitis. (a) (b) 1 improved outcomes in colon and rectal surgery extension (Figure 11.55), and has an advantage over CT in the evaluation of tumoral invasion. metabolic activity (including carcinoid and mucinous adenocarcinoma) have a higher likelihood of a false-negative result.(261, 262) Gastrointestinal Scintigraphy Nuclear medicine scintigraphy is. metastasectomy.(251) Endoluminal Ultrasound Endoluminal ultrasound’s (EUS) impact on the workup for colorectal cancer continues to expand. Transrectal US appears to be the most accurate imaging modality in determining

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