Anatomic and pathologic findings at external phased-array pelvic MR imaging after surgery for anorectal disease

MRI anatomy of the rectum: key concepts important for rectal cancer staging and treatment planning

A good understanding of the MRI anatomy of the rectum and its surroundings is pivotal to ensure high-quality diagnostic evaluation and reporting of rectal cancer. With this pictorial review, we aim to provide an image-based overview of key anatomical concepts essential for treatment planning, response evaluation and post-operative assessment. These concepts include the cross-sectional anatomy of the rectal wall in relation to T-staging; differences in staging and treatment between anal and rectal cancer; landmarks used to define the upper and lower boundaries of the rectum; the anatomy of the pelvic floor and anal canal, the mesorectal fascia, peritoneum and peritoneal reflection; and guides to help discern different pelvic lymph node stations on MRI to properly stage regional and non-regional rectal lymph node metastases. Finally, this review will highlight key aspects of post-treatment anatomy, including the assessment of radiation-induced changes and the evaluation of the post-operative pelvis after different surgical resection and reconstruction techniques.

Imaging of Abdominal Postoperative Complications

We present a case-based review of abdominal postoperative complications, organized by organ system affected, including wound/superficial, hepatobiliary, pancreatic, gastrointestinal, genitourinary, and vascular complications. Both general complications and specific considerations for certain types of operations are described, as well as potential pitfalls that can be confused with complications. Representative cases are shown using all relevant imaging modalities, including CT, fluoroscopy, ultrasound, MRI, and nuclear medicine. Management options are also described, highlighting those that require radiologist input or intervention.

Role of MRI and added value of diffusion-weighted and gadolinium-enhanced MRI for the diagnosis of local recurrence from rectal cancer

PURPOSE

To evaluate whether the addition of gadolinium-enhanced MRI and diffusion-weighted imaging (DWI) improves T2 sequence performance for the diagnosis of local recurrence (LR) from rectal cancer and to assess which approach is better at formulating this diagnosis among readers with different experience.

METHODS

Forty-three patients with suspected LR underwent pelvic MRI with T2 weighted (T2) sequences, gadolinium fat-suppressed T1 weighted sequences (post-contrast T1), and DWI sequences. Three readers (expert: G, intermediate: E, resident: V) scored the likelihood of LR on T2, T2 + post-contrast T1, T2 + DWI, and T2 + post-contrast T1 + DWI.

RESULTS

In total, 18/43 patients had LR; on T2 images, the expert reader achieved an area under the ROC curve (AUC) of 0.916, sensitivity of 88.9%, and specificity of 76%; the intermediate reader achieved values of 0.890, 88.9%, and 48%, respectively, and the resident achieved values of 0.852, 88.9%, and 48%, respectively. DWI significantly improved the AUC value for the expert radiologist by up to 0.999 (p = 0.04), while post-contrast T1 significantly improved the AUC for the resident by up to 0.950 (p = 0.04). For the intermediate reader, both the T2 + DWI AUC and T2 + post-contrast T1 AUC were better than the T2 AUC (0.976 and 0.980, respectively), but with no statistically significant difference. No statistically significant difference was achieved by any of the three readers by comparing either the T2 + DWI AUCs to the T2 + post-contrast T1 AUCs or the AUCs of the two pairs of sequences to those of the combined three sequences. Furthermore, using the T2 sequences alone, all of the readers achieved a fair number of "equivocal" cases: they decreased with the addition of either DWI or post-contrast T1 sequences and, for the two less experienced readers, they decreased even more with the three combined sequences.

CONCLUSIONS

Both DWI and T1 post-contrast MRI increased diagnostic performance for LR diagnosis compared to T2; however, no significant difference was observed by comparing the two different pairs of sequences with the three combined sequences.

MR imaging of perianal fistulas in Crohn's disease: sensitivity and specificity of STIR sequences

INTRODUCTION

Although some studies proved the role of STIR sequences in the evaluation of perianal fistulas in Crohn's Disease (CD), contrast medium is still injected in many institutions since there is not a validated reference MR protocol. Our purpose was to evaluate the role of the STIR sequence in the detection and characterization of perianal fistulae comparing it to the post-contrast T1 sequence and correlating it with rectal examination under anesthesia.

MATERIALS AND METHODS

We retrospectively reviewed all clinical records of 31 CD patients, suspected of having perianal fistulas, who had been submitted to an MR study before and after contrast medium injection and surgical exploration under anesthesia within the same month. Perianal fistulas were classified according to the Parks' criteria. Finally, comparison between STIR and post-contrast T1-weighted fat saturated sequences was done.

RESULTS

29 fistulas were detected in 25 patients who underwent an MR study. There was no significant difference between MR imaging and exploration under anesthesia. For the detection of perianal fistulas of any type, there was a perfect statistical agreement between gadolinium-enhanced and STIR sequences (kappa value = 1).

CONCLUSION

STIR sequences represent a valid alternative to the T1-weighted sequences acquired after the injection of contrast medium, allowing the identification of the primary fistula, any secondary ramification, and complications of the disease.

Magnetic resonance enterography in post-operative inflammatory bowel disease

OBJECTIVE

To describe the role of magnetic resonance enterography (MRE) in patients with inflammatory bowel disease (IBD), and to review the expected post-operative appearance, as well as, potential surgical complications in this unique patient population.

CONCLUSION

MRE compares favorably to CT Enterography (CTE) in terms of overall diagnostic accuracy and may provide better functional assessment of the small bowel through cine-MRI, diffusion-weighted imaging and dynamic contrast-enhancement. In the post-operative population, MRE provides critical information including: normal post-surgical anatomy, chronic strictures vs. active inflammation and disease/treatment-related complications. The post-operative IBD patient undergoes frequent repeated imaging and MRE may significantly reduce cumulative radiation dose while providing similar or improved diagnostic accuracy compared to CTE. MRE should be considered as an alternative imaging modality in this population.

Primary rectal cancer local staging

The treatment of patients with a malignant rectal tumor has evolved over the past few years. The role of medical imaging techniques, notably MRI, has become increasingly important in the preoperative assessment of rectal tumors. Radiologists are finding that their presence is requested more and more frequently at multidisciplinary team meetings for decision-making on the treatment of these tumors and therefore they must have a grounding in the therapeutic issues involved. Locoregional assessment of malignant rectal tumors may be performed prior to initiating treatment or as a re-evaluation following neoadjuvant therapy. We are interested in the assessment of the initial locoregional extension of these rectal tumors and we place much emphasis on the ability to identify MRI criteria which determine the patient's prognosis and treatment. We will also examine the advantages of MRI as well as its limits in this assessment.

Value of diffusion-weighted and gadolinium-enhanced MRI for the diagnosis of pelvic recurrence from colorectal cancer

PURPOSE

To prospectively assess the added value of gadolinium-enhanced and diffusion-weighted (DWI) MRI for the diagnosis of pelvic recurrence from colorectal cancer (CRC).

MATERIALS AND METHODS

Fifty-two patients with suspected pelvic recurrence from CRC underwent pelvic MRI with T2-weighted ("T2"), gadolinium-enhanced fat-suppressed T1-weighted ("gadolinium") and DWI MR sequences. Three readers (senior radiologist: R1, two residents: R2, R3) scored the likelihood of recurrence on "T2," "T2 + DWI," and "T2 + Gadolinium."

RESULTS

Twenty-seven patients had 42 sites of pelvic recurrence. On "T2," R1 achieved AUC of .95, sensitivity 88.4%, specificity 95.2%. For R2, these figures were .89, 81.4%, 90.5%, for R3 .90, 83.7%, 76%. Both Gadolinium injection and DWI significantly improved AUCs for residents but not for the senior radiologist: up to .988 (R2, P = 0.006) and to .98 (R3, P = 0.01) with DWI and to .96 (R2, P = 0.04), .98 (R3, P = 0.01) after gadolinium. All readers achieved slightly better AUCs with "T2 + DWI" than with "T2+Gadolinium" but not significantly (P = 0.68, P = 0.11, P = 0.3; respectively).

CONCLUSION

For diagnosis of pelvic recurrence from CRC, both DWI and gadolinium-enhanced MRI significantly increase diagnostic performances compared with "T2" MRI for residents. DWI may be helpful in patients with contra-indications to intravenous administration of gadolinium.

MR imaging features of nongynaecologic cystic lesions of the pelvis

OBJECTIVE

The purpose of our article is to review the magnetic resonance imaging (MRI) features of nongynaecologic cystic lesions of the pelvis.

CONCLUSION

The rising use of MRI for pelvic exploration will result in an increase in incidental detection of pelvic cystic cysts. Pelvic cysts of non gynecologic origin are less frequent than gynecologic cysts. However, they account for a wide range of abnormalities, and radiologists must be aware of their features and characteristics.

[3.0T MRI with a high resolution protocol for the study of benign disease of the anus and rectum. Part 2: Anorectal inflammatory disease. Postsurgical anatomy and complications after treatment]

Benign anorectal disease comprises a broad group of processes with very diverse origins; these processes may be congenital or acquired as well as inflammatory or tumor related. However, benign anorectal disease has received less attention in the scientific literature than malignant disease. In this second part of this image-based review of benign anorectal disease, we describe the most common inflammatory and fistulous diseases, the postsurgical anatomy, and complications that can occur after surgical treatment or radiotherapy for anorectal disease.

MRI and pelvic abscesses: a pictorial review

OBJECTIVE

The purpose of our article was to review the magnetic resonance imaging (MRI) features of pelvic abscesses. Pelvic abscesses account for a wide range of abnormalities from various etiologies.

CONCLUSION

MRI is being increasingly used for pelvic exploration. Radiologists must thus be aware of their features and characteristics.

Ileal pouch and related complications: spectrum of imaging findings with emphasis on MRI

Proctocolectomy with ileal pouch-anal anastomosis (IPAA) is the established surgical therapy for familial adenomatous polyposis (FAP) and refractory ulcerative colitis (UC). Despite general patient satisfaction with preserved fecal continence, this procedure is associated with a significant long-term morbidity approaching 70% after 10 years, and with a non-negligible rate of pouch failure leading to removal and permanent ileostomy. Following a concise description of the surgical technique, the normal imaging appearance of the ileal "pouch" reservoir at pelvic CT and MRI is explained. Since awareness of their imaging appearances is needed for a correct diagnosis, we discuss and illustrate common and unusual pouch-related complications, including pouchitis and irritable pouch disease; anastomotic leakages and pelvic abscess collections; fistulas involving the ano-perianal region, urinary bladder, vagina, perineal skin, and subcutaneous planes; anal stenosis and small-bowel obstruction. In our experience, pelvic contrast-enhanced MRI has proven invaluable for the diagnostic assessment of patients with suspected pouch-related complications, allowing differentiation of uncomplicated pouchitis from pelvic sepsis, the latter requiring aggressive therapy and possible even in patients with normal endoscopic findings.

Colonic transformation of ileal pouch-anal anastomosis and of the distal ileum: MRI findings

Colonic metaplasia of the ileal reservoir in patients after ileal pouch-anal anastomosis (IPAA) is described in pathological and histochemical studies. So far, there are no reports on the imaging presentation of colonic transformation. We describe the distinctive post-operative MRI features found in a 28-year-old patient with IPAA after failed conservative treatment of chronic ulcerative colitis. These distinct MRI features of colonic transformation of ileum mimicking normal colon are important to know for radiologists reading MR examinations of patients with IPAA.

Magnetic resonance imaging of rectal cancer

Magnetic resonance imaging (MRI)is a useful modality for the evaluation of rectal cancer, providing superior anatomic/pathologic visualization when compared with endorectal ultrasound (EUS) and computed tomography (CT). Preoperative MRI is useful for tissue characterization and tumor staging, which determines the surgical approach and need for neoadjuvant/adjuvant therapy. Important prognostic factors include the circumferential resection margin (CRM), T and N stages, and extent of local invasion. Postoperative MRI to assess the extent of tumor recurrence enables early resection, which can greatly prolong survival. MRI criteria for local recurrence include T2 hyperintensity, early dynamic rim enhancement, and nodular morphology. Future research in MRI of rectal cancer is geared toward developing optimal imaging techniques including high-resolution MRI, whole-body scans, and parallel imaging; imaging of lymph nodes by MR lymphography; and response to therapy using diffusion/perfusion-weighted MR and functional imaging.

Long-term outcomes with the use of bioprosthetic plugs for the management of complex anal fistulas

PURPOSE

This study was undertaken to determine the long-term outcomes of patients whose anal fistulas were managed by use of bioprosthetic plugs.

METHOD

A retrospective analysis was performed of all patients whose anal fistula was managed by use of a bioprosthetic plug between May 2005 and September 2006, who had a minimum of 1 year of follow-up since their last treatment. Patients whose fistulas were clinically healed were offered MRI to confirm healing of the fistula.

RESULTS

The bioprosthetic fistula plug was used to treat an anal fistula in 63 patients with clinical healing of the fistula in 51 (81%). Multivariate analysis showed that tobacco smoking, posterior fistula, and history of previous failure of the bioprosthetic plug was predictive of failure of the bioprosthetic plug. Eight patients with clinical healing after a minimum of 1 year since their last treatment underwent MRI. No evidence of residual fistula tract or fluid in the area of the previous fistula was found in 6 (75%) of these patients.

CONCLUSION

Bioprosthetic plugs are effective for the long-term closure of complex fistulas-in-ano. Randomized clinical trials comparing bioprosthetic plugs with other sphincter-preserving methods for fistula management need to be conducted to further determine the role of bioprosthetics in the management of anal fistulas.

[Postoperative imaging after colorectal surgery]

Surgery for the treatment of colorectal diseases has been evolving rapidly recently. In addition to classical surgical procedures (colectomy, abdominoperineal resection), new surgical procedures include coloproctectomy with creation of an ileoanal anastomosis and ileal pouch, pelvic reconstructions (omentoplasty, placement of myocutaneous flaps) and creation of different colic anastomoses after anterior rectal resection. Even if computed tomography and fluoroscopic contrast examinations are still commonly used to assess postoperative changes and complications, especially infections, pelvic magnetic resonance imaging is useful to depict postoperative changes, detect complications such as fistulas and tumor recurrence in patients who have undergone surgery for primary or recurrent rectal disease. The main surgical techniques, their respective indications and postsurgical imaging features will be discussed. The main complications and imaging work-up will also be reviewed.

Magnetic resonance imaging in locoregional staging of rectal adenocarcinoma

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.

[Newer techniques in diagnostic imaging of colorectal carcinoma]

A wide spectrum of nowadays availible radiological and imaging methods in the diagnostic evaluation of patients with colorectal cancer enabled not only the improvement of primary colorectal malignancy detection, precise staging, regional involvement and metastatic spread assessment, but also the posttherapeutical estimation and follow-up. Having in mind that the exact diagnostic assessment of colorectal carcinoma by use of different imaging modalities still raises a lots of contradictories, in this report we have tried to present the possibilities of newer imaging techniques in the diagnostic evaluation of the patients with colorectal cancer.