Radiology of anal and lower rectal cancers

Expert Panel on Gastrointestinal Imaging, Horvat N, Liu PS, Fowler KJ, Birkholz JH, Cash BD, Dane B, Eng C, Kambadakone AR, Korngold EK, Pietryga JA, Refaat T, Santillan CS, Surasi DS, Woolsey S, Kim DH. ACR Appropriateness Criteria® Staging and Follow-up of Anal Cancer

This document aims to provide recommendations on the role of imaging in the diagnosis of squamous cell anal cancer, focusing on its use in locoregional and systemic assessment during initial staging, posttreatment evaluation, and surveillance. For initial locoregional staging, MRI of the pelvis and FDG-PET/CT are usually appropriate to complement clinical and digital rectal examinations, because they offer additional information regarding locoregional tumor invasion and nodal metastases. For metastatic disease assessment, which is rare in the initial presentation and commonly associated with recurrence-with lymph nodes, liver, and lungs being the most common sites of disease-CT and FDG-PET/CT are usually appropriate for detecting distant nodal metastases and other sites of metastatic disease. MRI of the abdomen may be appropriate as a problem-solving tool, particularly in assessing small or indeterminate liver lesions. For patients who have completed locoregional treatment, most typically achieve clinical complete response; consequently, few require surgery unless there is persistent disease or recurrence. The role of posttreatment imaging assessment is still debatable; however, in cases in which surgery is indicated, MRI and FDG-PET/CT are usually appropriate for assessing local tumor invasion and nodal metastases. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances in which peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

MR Imaging of Anal Cancer

Anal cancer represents a rare type of gastrointestinal malignancy with anal squamous cell carcinoma as the most common histologic type. This review aims to present up-to-date imaging recommendations for anal cancer, including for baseline staging and follow-up assessment after treatment, with an emphasis on the role of MR imaging. Treatment complications are also discussed, helping to familiarize radiologists to include them in their search patterns. Lastly, a short discussion on the future horizon of anal cancer imaging is presented.

An Updated Review on Imaging and Staging of Anal Cancer-Not Just Rectal Cancer

Anal cancer is a rare disease, but its incidence has been increasing steadily. Primary staging and assessment after chemoradiation therapy are commonly performed using MRI, which is considered to be the preferred imaging modality. CT and PET/CT are useful in evaluating lymph node metastases and distant metastatic disease. Anal squamous-cell carcinoma (ASCC) and rectal adenocarcinoma are typically indistinguishable on MRI, and a biopsy prior to imaging is necessary to accurately stage the tumor and determine the treatment approach. This review discusses the histology, MR technique, diagnosis, staging, and treatment of anal cancer, with a particular focus on the differences in TNM staging between anal and rectal carcinomas.

PURPOSE

This review discusses the histology, MR technique, diagnosis, staging, and treatment of anal cancer, with a particular focus on the differences in TNM staging between anal squamous-cell carcinoma (ASCC) and rectal adenocarcinoma.

METHODS AND MATERIALS

To conduct this updated review, a comprehensive literature search was performed using prominent medical databases, including PubMed and Embase. The search was limited to articles published within the last 10 years (2013-2023) to ensure their relevance to the current state of knowledge.

INCLUSION CRITERIA

(1) articles that provided substantial information on the diagnostic techniques used for ASCC, mainly focusing on imaging, were included; (2) studies reporting on emerging technologies; (3) English-language articles.

EXCLUSION CRITERIA

articles that did not meet the inclusion criteria, case reports, or articles with insufficient data. The primary outcome of this review is to assess the accuracy and efficacy of different diagnostic modalities, including CT, MRI, and PET, in diagnosing ASCC. The secondary outcomes are as follows: (1) to identify any advancements or innovations in diagnostic techniques for ASCC over the past decade; (2) to highlight the challenges and limitations of the diagnostic process.

RESULTS

ASCC is a rare disease; however, its incidence has been steadily increasing. Primary staging and assessment after chemoradiation therapy are commonly performed using MRI, which is considered to be the preferred imaging modality. CT and PET/CT are useful in evaluating lymph node metastases and distant metastatic disease.

CONCLUSION

ASCC and rectal adenocarcinoma are the most common histological subtypes and are typically indistinguishable on MRI; therefore, a biopsy prior to imaging is necessary to stage the tumor accurately and determine the treatment approach.