ARRS 2022 Abstracts


E1806. The Pearls and Pitfalls of Rectal Cancer Staging by CT
  1. Imran Ahmed; University of Cincinnati
  2. Miguel Huerta; University of Cincinnati
  3. Juliana Tobler; University of Cincinnati
  4. Shaun Wahab; University of Cincinnati
  5. Kyuran Choe; University of Cincinnati
Accurate staging of rectal cancer is critical in guiding treatment and surgical planning. MRI is becoming the standard for preoperative rectal cancer staging and assessment of treatment response. The high spatial resolution of T2-weighted imaging allows for accurate characterization of tumor location and its relationship to surrounding structures. However, in patients unable to undergo MRI, CT in conjunction with transrectal sonography may provide useful staging and pre-operative information.

Educational Goals / Teaching Points
After reviewing this exhibit, learners will understand the features that distinguish rectal tumor staging, including tumor size and invasion as well as local and distant disease. The exhibit includes rectal cancer cases from our institution with CT and MRI correlates highlighting the pearls and pitfalls of attempting to stage by CT. The accuracy of staging by CT is increased with mid and high rectal tumors, T3 and T4 tumors, and tumors presenting with distant metastatic disease. Pitfalls of CT staging of rectal tumors are presented to demonstrate instances where accuracy is less reliable, which include low rectal tumors, T1 and T2 tumors, and desmoplastic reaction versus early T3 tumors.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The exhibit will highlight the various stages of rectal cancer and associated findings on CT with MRI correlation. The advantages and disadvantages of the use of CT to stage rectal tumors are discussed with case examples. Mesorectal fascia invasion is more accurately assessed in mid and upper rectal tumors and is less reliable with low rectal tumors due to thin peri-rectal fat inferiorly. Imaging findings that impact prognosis are also discussed, which include loco-regional lymph node metastasis and extramural vascular invasion (EMVI). Due to lower soft tissue contrast resolution of CT compared to MRI, distinguishing between T1 and T2 stage is unreliable. We also review the challenges in distinguishing between desmoplastic reaction and tumor infiltration, which often leads to over-staging of T1 and T2 tumors as T3 tumors. Additionally, imaging techniques are discussed, which include obtaining thin (1 mm) slices, allowing for multi-planar reformats to improve staging accuracy.

In patients who are unable to undergo MRI, CT may be useful for staging T3 and T4 rectal tumors in addition to assessing for extramural vascular invasion, loco-regional lymph node, and distant metastasis. The radiologist should be aware of the limitations of CT, imaging technique, pertinent findings, and potential pitfalls that could lead to over staging of tumors.