Despite advances in neoadjuvant and adjuvant therapy, attention to proper surgical technique, and improved pathological staging for both the primary and metastatic lesions, almost half of all colorectal cancer patients will develop recurrent disease. More concerning, this includes ~25% of patients with theoretically curable node-negative, non-metastatic Stage I and II disease. Given the annual incidence of colorectal cancer, approximately 150,000 new patients are candidates each year for follow-up surveillance. When combined with the greater population already enrolled in a surveillance protocol, this translates to a tremendous number of patients at risk for recurrence. It is therefore imperative that strategies aim for detection of recurrence as early as possible to allow initiation of treatment that may still result in cure. Yet, controversy exists regarding the optimal surveillance strategy (high-intensity vs. traditional), ideal testing regimen, and overall effectiveness. While benefits may involve earlier detection of recurrence, psychological welfare improvement, and greater overall survival, this must be weighed against the potential disadvantages including more invasive tests, higher rates of reoperation, and increased costs. In this review, we will examine the current options available and challenges surrounding colorectal cancer surveillance and early detection of recurrence.

Due to their high magnetization, superparamagnetic iron oxide nanoparticles induce an important decrease in the transverse relaxation of water protons and are, therefore, very efficient negative MRI contrast agents. The knowledge and control of the chemical and physical characteristics of nanoparticles are of great importance. The choice of the synthesis method (microemulsions, sol-gel synthesis, laser pyrolysis, sonochemical synthesis or coprecipitation) determines the magnetic nanoparticle's size and shape, as well as its size distribution and surface chemistry. Nanoparticles can be used for numerous in vivo applications, such as MRI contrast enhancement and hyperthermia drug delivery. New developments focus on targeting through molecular imaging and cell tracking.

A comprehensive overview of the current status of magnetic resonance imaging (MRI) in the locoregional assessment and management of rectal adenocarcinoma is presented. Staging systems for rectal cancer and treatment strategies in its management are discussed to give the reader the context that shapes MRI acquisition techniques and interpretation. Findings on MRI are detailed and their accuracy reviewed based on currently available evidence. Optimization of MRI acquisition and relevant pelvic anatomy are reviewed. A detailed description of our approach in interpreting MRI for locoregional staging of rectal cancer is given and future directions are also introduced.

MRI is the standard modality in the pre- and post-treatment evaluation of patients with rectal cancer, particularly in those cases with locally advanced disease. We routinely employ a superparamagnetic iron oxide (SPIO) contrast enema to distend the rectal lumen and achieve maximal tumor-to-lumen contrast gradient. This practice also allowed the identification of a fistula in 24% of patients treated for rectal cancer. Contrast agent-related low intensity signal could be seen filling the tract and eventually opacifying surrounding organs (i.e., vagina) or collections (i.e., presacral abscess). Fistula formation after radiochemotherapy and surgery for rectal cancer is not uncommon. MRI with dark lumen contrast enema allows an effective demonstration of this complication in a high number of patients.

Local recurrence (LR) after curative surgery for rectal cancer occurs in 4 to 33% of cases especially if surgery is sub-optimal (without total excision of the mesorectum). In many cases, diagnosis of LR is made at a late stage because of the high rate of asymptomatic patients, 56% in the experience of the Mayo Clinic. MRI and PETscan are most effective for assessing local and general extension, with a high diagnostic accuracy. Surgical treatment alone or with radiation (preoperative and/or intraoperative) is the only curative treatment of LR with R0 resectability rates of 30% to 45%. Morbidity and mortality rates are high, especially for total exenteration and abdomino-sacral resection. After curative surgery, 5-year global survival is between 30% and 40%. Palliative resection of macroscopic residues is not recommended. Careful patient selection for curative surgery is the best way to optimize treatment in these cases.

Pelvic magnetic resonance (MR) imaging is useful for identification of postoperative changes, complications, and disease recurrence in patients who have undergone surgery for primary or recurrent anorectal disease. Commonly used interventions include treatment for anorectal carcinoma: anterior rectal resection with or without creation of different colic anastomoses and abdominoperineal excision with or without pelvic reconstruction (omentoplasty, placement of myocutaneous flaps). Other common interventions include treatment for inflammatory bowel disease (coloproctectomy with or without creation of an ileoanal anastomosis and ileal pouch) and treatment for fistulas (placement of flaps or setons). Postoperative anatomic changes and formation of scar tissue can usually be identified with consecutive MR imaging examinations. Pelvic MR imaging is an accurate technique for assessment of complications including anastomotic leakage, septic complications such as fistulas and abscesses, neoplastic recurrence, and other less common complications (perineal hernia, peritoneal pseudocyst). The sophisticated surgical procedures used in rectal surgery can alter normal anatomy and make image interpretation difficult. Thus, familiarity with the appearances of postoperative anatomic changes, complications, and tumor recurrence is essential for accurate MR imaging evaluation after surgery for anorectal disease.

Local disease is the most frequent recurrence pattern of rectal carcinoma, and its prognosis is not good. One reason for the poor prognosis is the difficulty of making the diagnosis at an early stage. To detect local recurrence as early as possible, we produced the monoclonal antibody, A7-gadolinium (Mab A7-Gd), conjugate as a contrast agent for magnetic resonance imaging to distinguish between carcinoma and normal tissue.

We examined the in vitro immunoreactivity of Mab A7 coupled to Gd by chelate, and stability of Mab A7-EDTA-Gd in human serum. Its in vivo distribution in nude mice with human colorectal carcinoma was also examined.

Mab A7-Gd retained binding activities that were nearly identical to intact Mab A7. Mab A7-Gd was stable in human serum. More radiolabeled Mab A7-Gd accumulated in the tumor than normal mouse IgG-Gd. Both Mab A7-Gd and normal mouse IgG-Gd disappeared from blood linearly over time. Accumulation levels in normal tissues decreased linearly over time but were lower than those in tumors.

Mab A7 conjugated to gadolinium selectively accumulated in the tumor. Our results suggest that it is potentially suitable as a contrast agent for MR imaging to detect local rectal carcinoma recurrence.

To determine if routine follow-up by magnetic resonance imaging (MRI) improves the detection of resectable local recurrences from colorectal cancer.

Surgical treatment offers the best prospect of survival for patients with recurrent colorectal cancer. Unfortunately, most cases are often diagnosed at an unresectable stage when traditional follow-up methods are used. The impact of MRI surveillance on the early diagnosis of local recurrences has yet to be ascertained.

Patients who underwent curative surgery for rectal and left-sided colon tumors were included in a program of pelvic surveillance by routine MRI, in addition to the standard follow-up protocol. Cases were then analyzed for mode of diagnosis, resectability, and overall survival.

Pelvic recurrence was found in 30 (13%) of the 226 patients studied. MRI detected 26 of 30 (87%) and missed 4 of 30 (13%) cases with local recurrence. Of the latter, 3 were anastomotic recurrences. In 28 (14%) patients, local recurrence was suspected by an initial MR scan but cleared by subsequent MRI or CT-guided biopsy. Recurrent pelvic cancer was diagnosed by MRI with 87% sensitivity and 86% specificity. In 19 (63%) cases, CEA was abnormally elevated, and 9 patients (30%) were symptomatic. Surgical resection was possible in only 6 patients (20%). There was no difference between MRI and conventional follow-up tests in their ability to detect cases suitable for surgery.

Pelvic surveillance by MRI is not justified as part of the routine follow-up after a curative resection for colorectal cancer and should be reserved for selectively imaging patients with clinical, colonoscopic, and/or biochemical suspicion of recurrent disease.

Radiology has a significant role in the evaluation of surgery for rectal cancer. With recent developments in surgical techniques, the number of neorectal reservoir configurations has increased. It is important to recognize the normal and abnormal appearances, both early and late, following pelvic surgery. The aim of this pictorial review is to demonstrate the imaging techniques that are used in both the investigation and the follow-up of patients who have undergone uncomplicated or complicated rectal resection.

The optimum strategy for pre-operative staging of colorectal carcinoma (CRC) has yet to be defined. A protocol for staging CRC patients was set up in this hospital in 1998. The protocol included complete colonic visualization together with assessment of the liver and lung for potential metastatic disease. Pelvic imaging was required to assess the local spread of rectal tumours. Our aim was to evaluate prospectively this protocol.

Data from all patients diagnosed with primary CRC between January 1999 and December 2002 were prospectively collected and analysed.

There were 295 patients; 56 (19%) patients presented as an emergency and were excluded. The study group consisted of 239 patients (206 had elective surgery and 33 had no resectional surgery). In the patients who presented electively; 88% had complete colonic imaging; 87% chest imaging; 90% had liver imaging; 91% of rectal tumours had pelvic imaging. Overall 75% of the elective patients completed the staging protocol. Reasons for incomplete staging were numerous and most were justifiable. Findings which influenced clinical management included alteration in surgical approach (14), lung metastases (7), primary lung cancers (2), definite liver metastases (25), possible liver metastases (8), neo-adjuvant radiotherapy required (27), advanced local disease (9) and other incidental findings (12).

Our protocol influenced further management decisions in 39% of patients. Better stratification of patient care is possible, with the ultimate aim to avoid unnecessary surgery. However, complete staging is not always possible to perform.

It has been suggested that MRI may be used as the sole modality of choice in pre-operative staging in rectal cancers. Knowledge of tumour stage and a threatened Circumferential Resection Margin (CRM) pre-operatively are essential for planning neo-adjuvant therapy and as predictors of local recurrence. At present most units utilize CT scanning to assess these parameters. The aim of our study was two fold: firstly to examine the accuracy of preop CT and MRI staging of rectal cancers compared with final histology and secondly to assess the accuracy of MRI in predicting penetration of the mesorectal envelope (ME).

All patients with biopsy proven rectal adenocarcinoma underwent thin slice MRI and CT scan pre-operatively. Forty-seven patients have been prospectively entered into the study: 24 male (median age 68 years; range 38-91 years). Eleven patients were unsuitable for surgery leaving 36 patients available for study.

CT correctly staged patients with T1/T2 rectal cancers more often than MRI (77% vs. 43%, P = 0.226). Patients with T1/T2 tumours were overstaged more often by MRI compared with CT (54% vs. 23%, P = 0.226). A greater proportion of patients with T3 tumours were correctly staged by MRI than CT (76% vs. 41%, P = 0.08); and more T3 disease was understaged by CT than MRI (54 vs. 18%, P = 0.032). CT and MRI staged T4 disease equally. In the assessment of mesorectal envelope integrity, MRI had a sensitivity of 80% and a specificity of 84%. The positive predictive value was 44% and the negative predictive value 96%.

These results suggest significant differences between accurate pre-operative "T" staging by CT and MRI for rectal cancer. MRI has the potential however, to accurately assess mesorectal envelope invasion. Further analysis is required to assess whether MRI can be used as the sole modality in pre-operative staging of rectal cancers.

Colorectal carcinomas are the most common gastrointestinal tract tumors. 50-60% of the colorectal carcinomas originate in rectum and sigmoid colon. The new developments in imaging modalities have brought improvements in therapeutic aspects. The survival rates in these patients depend on the tumor penetration and the presence of regional lymph node or distant metastasis. The recurrence rates have decreased with the new operation techniques and preoperative radiotherapy, thus increasing the importance of accurate tumor staging. Double contrast barium enema studies enable the diagnosis while staging and follow-up is best done by topographic imaging techniques.