Endoscopic MRI using 3D-spoiled GRASS (SPGR) sequence for local staging of rectal carcinoma

Preoperative evaluation of colorectal cancer

Surgery is a primary modality for the treatment of patients with colorectal cancer. Before any surgical therapy, patients diagnosed with colorectal cancer require an evaluation. This preoperative evaluation can be used to assess the patient's risk associated with surgery, plan the surgical resection, and stage the patient's cancer. Staging of the cancer preoperatively is primarily of concern in rectal cancer patients. This article focuses on the elective surgical setting and the recommended preoperative evaluation of patients who have been diagnosed with colorectal cancer.

IRM et exploration du tube digestif — Aspects techniques et perspectives d’évolution

Barium enema remains the reference method for the detection of morphological intraluminal alterations of the bowel. Optimal filling of intestinal loops allows high diagnostic sensitivity and specificity. US, CT and MRI are useful diagnostic procedures in the evaluation of mural and extramural alterations. In recent years, MR-enteroclysis and MR colonography have been developed, both enable the evaluation of luminal, extraluminal and mural alterations of the bowel. While these modalities provide good imaging evaluation of the bowel, visualization of the different layers, as seen on US, is still not available. Use of high resolution endoluminal coil on MR could improve mural evaluation of bowel to differentiate inflammatory diseases and provide accurate TNM classification of tumoral lesion with minimally invasive procedure.

Surgeon-performed ultrasound: endorectal ultrasound

Endorectal (ERUS) and endoanal (EAUS) ultrasound imaging is increasingly being performed by surgeons in the office and outpatient setting for the assessment of both benign and malignant disease. Multiple studies have demonstrated the accuracy of these modalities in identifying pertinent anatomy and anatomic abnormalities. The ultrasound is easily tolerated by most patients, and is easily performed with minimal preparation on the patient's part. The ability of the surgeon to perform and interpret this straight forward diagnostic procedure allows for the simplification of the diagnostic process and a more rapid determination of treatment options for the patient.

Rectal cancer: local staging and assessment of lymph node involvement with endoluminal US, CT, and MR imaging--a meta-analysis

PURPOSE

To perform a meta-analysis to compare endoluminal ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging in rectal cancer staging.

MATERIALS AND METHODS

Relevant articles published between 1985 and 2002 were included if more than 20 patients were studied, histopathologic findings were the reference standard, and data were presented for 2 x 2 tables; articles were excluded if data were reported elsewhere in more detail. Two reviewers independently extracted data on study characteristics and results. Bivariate random-effects approach was used to obtain summary estimates of sensitivity and specificity for invasion of muscularis propria, perirectal tissue, and adjacent organs and for lymph node involvement. Summary receiver operating characteristic (ROC) curves were fitted for perirectal tissue invasion and lymph node involvement.

RESULTS

Ninety articles fulfilled all inclusion criteria. For muscularis propria invasion, US and MR imaging had similar sensitivities; specificity of US (86% [95% confidence interval [CI]: 80, 90]) was significantly higher than that of MR imaging (69% [95% CI: 52, 82]) (P =.02). For perirectal tissue invasion, sensitivity of US (90% [95% CI: 88, 92]) was significantly higher than that of CT (79% [95% CI: 74, 84]) (P <.001) and MR imaging (82% [95% CI: 74, 87]) (P =.003); specificities were comparable. For adjacent organ invasion and lymph node involvement, estimates for US, CT, and MR imaging were comparable. Summary ROC curve for US of perirectal tissue invasion showed better diagnostic accuracy than that of CT and MR imaging. Summary ROC curves for lymph node involvement showed no differences in accuracy.

CONCLUSION

For local invasion, endoluminal US was most accurate and can be helpful in screening patients for available therapeutic strategies.

In vitro rat colonic wall imaging with MR endoluminal coil: feasibility study and histologic correlations

RATIONALE AND OBJECTIVES

Despite improvements, spatial resolution and image quality with routine surface coils are too limited when detailed information about the gastrointestinal layers is requested. The objective of our feasibility study was to evaluate the potential of a dedicated endoluminal coil to depict different layers of the colonic wall in an in vitro small animal model.

MATERIALS AND METHODS

A single-loop coil (40 mm length, 5 mm width) was built using IC (printed circuit) technology. The coil was tuned to a frequency of 63.7 MHz and matched at 50 Omega for this frequency. The coil was housed in a biocompatible tube with an outer diameter of 18 F (6 mm). Ten segments of rat colon, surgically excised 5 hours earlier, were completely immersed in an isotonic solution. The coil was introduced through the lumen of colonic specimens. MRI experiments were performed on a 1.5 T MR Symphony system (Siemens, Erlangen, Germany) using imaging protocol combining high-resolution 2D Flash, fast imaging employing steady-state acquisition (TrueFISP), turbo spin echo (TSE), and 3D FastLow-Angle Shot (FLASH) sequences. After a 24-hour period of fixation in 10% formalin, colonic specimens were excised along the longitudinal axis for histologic analysis.

RESULTS

The endoluminal coil provided high SNR allowing for the visualization of different layers of rat colonic walls. All the performed sequences made it possible to identify at least two different layers. On T1-weighted gradient-echo sequences, the mucosa was of high signal intensity, whereas the muscle layers had an intermediate to low signal intensity. The signal intensity of different wall layers was similar in different sequences. Histologic analysis identified three main layers.

CONCLUSION

These results are well correlated with histologic findings and suggest that endoluminal MR imaging may have potential for accurate staging of colonic tumor or inflammatory process.

Magnetic resonance imaging of bowel ischemia induced by ligation of superior mesenteric artery and vein in a cat model

OBJECTIVE

To assess the usefulness of magnetic resonance (MR) imaging for detecting bowel ischemia with strangulation compared with histopathologic findings in an experimental cat model.

MATERIALS AND METHODS

Fourteen cats were assigned to the normal control group (n = 3), acute ischemic group (induced by ligation of superior mesenteric vessels for 3 hours, n = 7), and subacute ischemic group (induced by ligation of superior mesenteric vessels for 10 hours, n = 4). Using a 4.7-T MR scanner, contrast-enhanced T1-weighted images were obtained at 0, 10, 20, 30, and 60 minutes after bolus injection of contrast media. T1- and T2-weighted images were obtained from the extracted bowel wall and compared with histopathologic findings.

RESULTS

On contrast-enhanced MR images, the target-like bowel wall layers were clearly demonstrated and the submucosal layer showed the most prominent enhancement. At 10 minutes after administration of contrast media, the subacute ischemic group showed significantly lower enhancement of the submucosal layer than the normal or acute ischemic group (P <0.05). On T1-weighted images, there were not significant differences between the normal and ischemic bowel groups (P >0.05). On T2-weighted images, the signal intensity of all layers of acute ischemic bowel wall was significantly higher than that of the normal control or subacute ischemic group (P <0.05).

CONCLUSION

Delayed contrast-enhanced MR images and T2-weighted images were helpful for detecting subacute and acute bowel ischemia with strangulation, respectively.

Colorectal carcinoma: radiological diagnosis and staging

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.

Early gastric carcinoma: evaluation with high-spatial-resolution MR imaging in vitro

PURPOSE

To determine signal intensity characteristics of the gastric wall layers and to assess the accuracy of the evaluation of early gastric carcinomas in vitro by using resected specimens studied with high-spatial-resolution magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Fifteen gastric specimens obtained from patients suspected of having early gastric carcinoma were studied with a 1.5-T MR system with a 4-cm-diameter loop coil. High-spatial-resolution spin-echo MR images were obtained with a field of view of 50 mm, a matrix of 256 x 256, and a section thickness of 2 mm, resulting in a voxel size of 0.08 mm(3). Findings from MR images were compared with histopathologic findings.

RESULTS

T1- and T2-weighted MR images clearly depicted the normal gastric wall as consisting of four and six layers, respectively, which corresponded well to the histologic layers. In 14 (93%) of 15 gastric carcinomas, the depth of mural invasion visualized with MR imaging correlated well with the histopathologic stage. The stage determined with MR imaging, however, was lower in one instance (7%) than the histopathologic stage. MR imaging also depicted the gross features of the tumor, presence of ulceration, and adjacent lymph node swelling.

CONCLUSION

High-spatial-resolution MR imaging has a high diagnostic accuracy in the evaluation of the mural invasion of early gastric carcinoma in vitro and thus potentially enables preoperative histopathologic staging.

Superficial esophageal carcinoma: an in vitro study of high-resolution MR imaging at 1.5T

The purpose of this study was to determine the diagnostic accuracy of high-resolution MR imaging at 1.5T for evaluating the mural invasion of superficial esophageal carcinoma. Forty-one esophageal specimens taken from patients suspected of having superficial carcinoma were studied using a 1.5T MR system with a surface coil. Spin-echo MR images were obtained with a field of view of 50mm, matrix of 256 x 256, and section thickness of 2mm (voxel size = 0.08 mm3). MR findings were compared with histopathologic findings. T2-weighted images clearly depicted the normal esophageal wall as consisting of 8 layers. In 39 (95%) of 41 carcinomas, the depth of mural invasion determined by MR imaging correlated well with that determined with histopathologic examination. The MR-based stage was higher in 2 (5%) cases than the histopathologic stage. High-resolution MR imaging at 1.5T shows a high diagnostic accuracy for evaluating the mural invasion of superficial esophageal carcinoma, thus potentially enabling preoperative histopathologic staging.

Imaging of anorectal disease

BACKGROUND

Over the past two decades developments in imaging have changed the assessment of patients with anorectal disease.

METHODS

The literature on imaging techniques for anorectal diseases was reviewed over the period 1980-1999.

RESULTS

For the staging of primary rectal tumours, phased array magnetic resonance imaging (MRI) may be regarded as the most appropriate single technique. The combination of endosonography or endoluminal MRI with ultrasonography or spiral computed tomography yields similar results. All techniques have limitations both for local staging and in the assessment of distant metastases. MRI or positron emission tomography is preferable for tumour recurrence. For perianal fistula, high-resolution MRI (phased array or endoluminal) is the technique of choice. For constipation, defaecography is the preferred technique, nowadays with emphasis on functional information. The role of magnetic resonance defaecography is currently being evaluated. For faecal incontinence, endosonography and endoluminal MRI give similar results in detecting sphincter defects; endoluminal MRI has the advantage of detecting external sphincter atrophy.

CONCLUSION

High-resolution MRI, endosonography and defaecography are currently the optimal imaging techniques for anorectal disease.

Results of EUS in detecting perirectal lymph node metastases of rectal cancer: the pathologist makes the difference

BACKGROUND

Accurate preoperative staging of primary rectal cancer is mandatory because the result may affect therapeutic decisions. Endoscopic ultrasonography (EUS) is considered the most accurate method for locoregional staging, but the issue of possible variations in the assessment of its accuracy related to technical aspects of pathologic staging has never been raised. The aim of this study was to assess EUS results as determined by two different methods of dissection of surgical specimens.

METHODS

Among all cases with primary rectal cancer staged with EUS from April 1991 to April 1997, 131 patients underwent surgery without preoperative radiotherapy; EUS results for nodal staging were compared with those obtained by pathology. Resected specimens were examined using two different techniques (conventional vs. special dissection).

RESULTS

There was a significant decrease in diagnostic accuracy of EUS according to pathologic technique. Overall accuracy, sensitivity, specificity, positive and negative predictive values for conventional versus special dissection were as follows: 74.6% vs. 43. 3% (p = 0.0001), 67.8% vs. 21.8% (p = 0.0002), 79.1% vs. 67.8% (p = 0.14), 67.8% vs. 43.7% ( p = 0.02), and 79.1% vs. 43.2% (p = 0.0003), respectively. EUS sensitivity according to size of metastatic lymph nodes was significantly lower for nodes smaller than 5 mm in diameter (p = 0.025) when special dissection was performed because of a larger number of lymph nodes harvested.

CONCLUSIONS

Our findings raise concern about the results of EUS staging of lymph node metastases in rectal cancer. Further prospective studies on a node-by-node basis could clarify the real diagnostic yield of EUS.

Endoluminal MR imaging of diseases of the anus and rectum

Endoluminal MRI of the rectum and anus was introduced in the first half of this decade to overcome the limitations of endoluminal sonography and body coil MRI. Endoluminal MRI is the imaging method of choice for fecal incontinence and anal tumors, whereas it is a competitive imaging method to phased array coil MRI in patients with perianal fistulas or rectal tumor. The purpose of this article is to describe the technique and major indications of endoluminal MR imaging of the anus and rectum.

Local staging of anal and distal colorectal tumors with the magnetic resonance endoscope

BACKGROUND

We prospectively assessed the feasibility and accuracy of endoscopic magnetic resonance (EMR) scanning in the local staging of anal and colorectal cancer as compared to endosonography.

METHODS

Fifteen patients with biopsy-proven anal (n = 2), rectal (n = 11), and distal colonic (n = 2) cancer underwent endosonography followed by EMR imaging. Scans were acquired using the magnetic resonance receiver coil incorporated into the tip of the non-ferromagnetic endoscope. Blinded to endosonography results, two radiologists interpreted the EMR images using the TNM system. Staging results were compared to endosonography in all patients and to histopathology in the 13 colorectal cases.

RESULTS

EMR imaging, well tolerated in all patients, correlated with endosonography in 10 of 15 and 12 of 15 cases for T- and N-staging, respectively. In the 13 colorectal patients with available histopathology, accuracy of EMR and of endosonography in T-staging was 77% and 85%, respectively; N-staging accuracy was 62% for both.

CONCLUSIONS

For anal and distal colorectal neoplasms, EMR imaging is feasible and provides local staging comparable to endosonography.

Primary tumour staging of gastric and colorectal cancer

Almost 15 years after its introduction, endosonography or endoscopic ultrasonography is an important technique in a wide range of gastrointestinal diseases. Other imaging techniques are CT, MRI and barium examination. There is a general consensus that the most important prognostic factor in gastric and colorectal carcinoma is the presence or absence of lymph node invasion, but malignant fixation of tumour through direct invasion of adjacent tissues also appears to be very important. Non-invasive preoperative assessment of tumour stage based on one or a combination of the above imaging modalities should allow appropriate treatment to be planned in each case.