Rectal Carcinoma

                       Gastrointestinal tract images  Rectal Carcinoma: Rectal wall penetration and pelvic lymph node involvement are the major prognostic factors in predicting recurrence. Some lymph nodes <5mm in diameter already contain metastases, a limitation in the imaging prediction of tumor spread. Nevertheless, the sensitivity for detecting positive lymph nodes is greater for rectal tumors than for more proximal colonic tumors because benign perirectal adenopathy is uncommon. The prevalence of lymph node involvement with rectal cancers is related to tumor depth. Among rectal cancers, lymph node involvement was as follows: T1, 6%; T2, 20%; T3, 66%; and T4, 79%. A biopsy finding of lymphatic vessel invasion was highly indicative of lymph node metastasis. 
                          pathway for the spread of sigmoid and high rectal cancers is via the inferior mesenteric lymph chain, but specific spread is unpredictable and can include the inferior mesenteric lymph nodes, nodes adjacent to rectum, and nodes at the root of the inferior mesenteric artery. A meta-analysis of articles published up to 2002 found that for muscularis propria invasion by a rectal cancer US and MR had similar sensitivities but US specificity was 86% and MR 69%; sensitivity for perirectal tissue invasion was: CT 79%, US 90% and MR 82%, with similar specificities. All three modalities were comparable for detecting lymph node involvement.
                      Multidetector CT is more accurate in staging more advanced rectal cancers than more superficial ones; CT does not provide rectal wall details. Adding multiplanar reconstruction improves local staging of these cancers. In 53 consecutive patients with distal rectal carcinoma, CT sensitivity for detecting perirectal and inferior mesenteric lymph node metastases was 53% and specificity 85%. Computed tomography using a water enema (hydro-CT) appears useful in staging rectal cancers. Hydro-CT studies tend to be more accurate than no enema studies; increased accuracy is mostly in detecting invasion within or beyond the muscular layers. A CT study of patients with rectal cancer using a tap water enema, IV contrast, and pharmacologic bowel hypotonia reached a sensitivity of 90% and specificity of 70% in differentiating tumors limited to bowel wall from those invading extrinsically. Conventional US has been largely supplanted by endorectal US in staging rectal carcinomas.
                      Endorectal US is very accurate in T-staging superficial cancers but not more advanced cancers because of limited acoustic range. Some authors express endorectal US staging using TNM nomenclature—called the uTNM classification. Although some results are promising, the overall conclusions are rather pessimistic, especially for detecting lymph node metastasis. Endoscopic resection should be possible if imaging could differentiate between mucosal and submucosal invasion. A number of stuties of early rectal cancer concluded that endoscopic US is not accurate enough to determine appropriate therapy for these tumors. On the other hand, a more recent study found that endorectal US achieved a sensitivity and specificity of 93% and 71%, respectively, and MRI 100% and 60% for detecting rectal wall penetration. Endorectal US does not reliably detect muscularis propria invasion (T2 tumors). Endorectal
US does, detect perirectal fat invasion (T3 tumors). Tumor spread to more distal structures, such as bladder, is more problematic.
                    Ultrasonography of the distal rectum is more difficult and the tissue planes are less well defined than more proximally, and endoscopic US staging accuracy in the distal rectum is lower than in the middle or proximal segments. On the other hand, endorectal US is accurate in evaluating anal canal infiltration by low rectal cancers. The overall tendency in staging rectal villous tumors with endoscopic US is to overstage rather than understage. Endoscopic US in patients with a rectal adenocarcinoma performed within 2 weeks prior to surgery and radiation therapy overstaged 21% and understaged 9% of patients. Overstaging of the depth of invasion is due, in part, to tumors located close to an uninvolved layer, not uncommon adjacent inflammation and hypervascularity, which tend toward a more anechoic appearance than tumor infiltration. Microscopic invasion accounts for some understaging.
                    After a rectal polypectomy with an adenocarcinoma discovered in the specimen, endorectal US detected residual tumor with a sensitivity of 100% but a specificity of only 44%. How accurate is endorectal US in detecting local lymph node invasion? Considerably more lymph nodes are involved at histologic examination than are detected by US, and a number of studies have concluded that endoscopic US is too unreliable to be used in preoperative patient selection. Some enlarged lymph nodes are due to reactive inflammation and not tumor infiltration. The ability to detect perirectal nodes varies with node size. In general, malignant nodes are larger than nonmalignant ones, although overlap exists.Metastatic nodes range from being partially to totally invaded. Similar
to metastatic nodes at other body sites, aside from node size, node metastases do not correlate with a specific imaging appearance. Several studies concluded that endoluminal US does not reliably identify the extent of lymph node involvement. The role of 3D endorectal US in staging rectal carcinoma remains to be established.
                    Whether patients are treated by radiotherapy or chemotherapy prior to surgery also appears to influence rectal US accuracy. Diagnostic US accuracy for wall infiltration and lymph node detection decreases after preoperative radiotherapy or chemoradiotherapy. In patients with known rectal tumors, endorectal US and MRI achieve comparable staging results. The advantages of endorectal US are its small-diameter instruments, its ready availability, it is technically less demanding, and it costs less; MRI, on the other hand, is operator independent and also evaluates other sites. Magnetic resonance imaging using an endorectal coil provides more detail than similar MRI using a surface coil. On the other hand, use of an endorectal coil combined with imaging using external coils appears advantageous in assessing both intramural tumor infiltration and more distal pelvic spread. Little data exists on placing such combined imaging in a proper perspective. High-spatial resolution MRI using T2- weighted FSE images identifies mesorectal fascia, peritoneal reflection, Denonvilliers fascia and adjacent structures. Magnetic resonance imaging has a tendency to understage rectal carcinomas. Overstaging in some patients is due primarily to the presence of adjacent perirectal inflammation.
This is radiology images of Rectal carcinoma. Precontrast (A) and contrast-enhanced (B) coronal T1–weighted MR images identify a left distal rectal tumor (arrows) invading perirectal fat.

                      Rectal distension by a water enema improves MR detection of rectal wall penetration.Using a rectal ferric ammonium citrate enema, spin echo MRI identifies most rectosigmoid cancers. Preoperative MR staging of rectal cancer achieved a 100% sensitivity and 70% specificity in distinguishing tumor stages worse than Dukes’ stage A; on T1-weighted images a rectal superparamagnetic contrast enema creates a signal void in a distended lumen while wall contrast enhancement by IV gadolinium differentiates mucosa, muscle layers, and perirectal space, details not obtainable with nonenhanced images. In a randomized phase II trial, preoperative MR using the superparamagnetic iron oxide rectal contrast agent ferristene and IV contrast achieved a sensitivity of 97% and specificity of 50% in staging carcinomas higher than T2 stage; using receiver operator characteristic (ROC) analysis, MR differentiated between T1/T2 and T3/T4 tumor stages with a ROC index of 0.85. Higher viscosity rectal contrast agent formulations were superior to lowviscosity formulations, but no significant differences were found between high and low iron content agents.
                       Similar to other imaging modalities, small lymph node metastases are not identified, although iv SPIO agents show promise. Nonmalignant nodes are hypointense or have a hypointense center, while eccentric and hyperintense nodes tend to contain metastases larger than 1mm in diameter, although overlap does exist. Can MRI predict sphincter salvage in these patients? A prospective MRI study of patients with a low or middle third rectal adenocarcinoma (defined as <12cm from pectinate line) using rectal and IV contrast and a flexible surface coil achieved 100% sensitivity and 98% specificity in assessing anal sphincter infiltration and 90% sensitivity and 100% specificity in detecting adjacent organ infiltration; nodal staging, however, was suboptimal MRI reached a 68% sensitivity and 24% specificity. Magnetic resonance imaging potentially differentiates between mucinous and nonmucinous rectal tumors. On T2-weighted fast SE images mucinous tumors had significantly higher tumor-to-muscle, tumor-tofat, and tumor-to-urine signal intensity ratios compared with nonmucinous tumors; most mucinous tumors also revealed peripheral post–gadolinium contrast enhancement.
Radiology images of A: Recurrent rectal carcinoma (arrow) in a patient with a prior rectal cancer resection and a side-to-end low colorectal anastomosis. B: Tumor recurrence at anastomosis in another patient. Barium enema reveals an irregular, ulcerated infiltrating tumor (arrows).

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