Magnetic resonance imaging in locoregional staging of rectal adenocarcinoma

An MRI-based multi-objective radiomics model predicts lymph node status in patients with rectal cancer

PURPOSE

To apply a multi-objective radiomics model based on pre-operative magnetic resonance imaging (MRI) for improving diagnostic accuracy of LN metastasis in rectal cancer patients.

METHODS

This study consisted of 91 patients diagnosed with rectal cancer from April 2018 to March 2019. All patients underwent rectal MRI before surgery without any other treatment. Clinical data, subjective radiologist assessments, and radiomic features of LNs were obtained. A total of 1409 radiomic features were extracted from T2WI LN images. Multi-objective optimization with the iterative multi-objective immune algorithm (IMIA) was used to select radiomic features to build prediction models. Predictive performances of radiomic, radiologist, and combined radiomic and radiologist models were assessed for accuracy by receiver operating characteristics (ROC) curves.

RESULTS

For the radiologist analysis, heterogeneity was the only significant independent predictor of LN status. The sensitivity, specificity, and accuracy of the subjective radiologist analysis were 72.09%, 73.81%, and 78.12%, respectively. The sensitivity, specificity, and accuracy of the solitary radiomic model consisting of 10 features were 89.81%, 82.57%, and 87.77%, respectively. The sensitivity, specificity, and accuracy of the combined model, which consisted of 12 radiomic and radiologist features, were 92.23%, 84.69%, and 89.88%, respectively. The combined model had the best prediction performance with an AUC of 0.94.

CONCLUSIONS

The multi-objective radiomics model based on T2WI images was very useful in predicting pre-operative LN status in rectal cancer patients.

Anorectal Cancer: Critical Anatomic and Staging Distinctions That Affect Use of Radiation Therapy

Although rectal and anal cancers are anatomically close, they are distinct entities with different histologic features, risk factors, staging systems, and treatment pathways. Imaging is at the core of initial clinical staging of these cancers and most commonly includes magnetic resonance imaging for local-regional staging and computed tomography for evaluation of metastatic disease. The details of the primary tumor and involvement of regional lymph nodes are crucial in determining if and how radiation therapy should be used in treatment of these cancers. Unfortunately, available imaging modalities have been shown to have imperfect accuracy for identification of nodal metastases and imaging features other than size. Staging of nonmetastatic rectal cancers is dependent on the depth of invasion (T stage) and the number of involved regional lymph nodes (N stage). Staging of nonmetastatic anal cancers is determined according to the size of the primary mass and the combination of regional nodal sites involved; the number of positive nodes at each site is not a consideration for staging. Patients with T3 rectal tumors and/or involvement of perirectal, mesenteric, and internal iliac lymph nodes receive radiation therapy. Almost all anal cancers warrant use of radiation therapy, but the extent and dose of the radiation fields is altered on the basis of both the size of the primary lesion and the presence and extent of nodal involvement. The radiologist must recognize and report these critical anatomic and staging distinctions, which affect use of radiation therapy in patients with anal and rectal cancers.

Evaluation of a rabbit rectal VX2 carcinoma model using computed tomography and magnetic resonance imaging

AIM: To establish a rabbit rectal VX2 carcinoma model for the study of rectal carcinoma.

METHODS: A suspension of VX2 cells was injected into the rectum wall under the guidance of X-ray fluoroscopy. Computed tomography (CT) and magnetic resonance imaging (MRI) were used to observe tumor growth and metastasis at different phases. Pathological changes and spontaneous survival time of the rabbits were recorded.

RESULTS: Two weeks after VX2 cell implantation, the tumor diameter ranged 4.1-5.8 mm and the success implantation rate was 81.8%. CT scanning showed low-density foci of the tumor in the rectum wall, while enhanced CT scanning demonstrated asymmetrical intensification in tumor foci. MRI scanning showed a low signal of the tumor on T₁-weighted imaging and a high signal of the tumor on T₂-weighted imaging. Both types of signals were intensified with enhanced MRI. Metastases to the liver and lung could be observed 6 wk after VX2 cell implantation, and a large area of necrosis appeared in the primary tumor. The spontaneous survival time of rabbits with cachexia and multiple organ failure was about 7 wk after VX2 cell implantation.

CONCLUSION: The rabbit rectal VX2 carcinoma model we established has a high stability, and can be used in the study of rectal carcinoma.