MRI Staging of Anorectal Malignancy—A Reporting Dilemma: Is It Adenocarcinoma or Squamous Cell Carcinoma?

Abstract

Aim Magnetic resonance imaging (MRI) of anorectal malignancy is often reported assuming low rectal adenocarcinoma (LRC). The biopsy may, however, reveal squamous cell carcinoma (SCC). Thus, the aim was to compare the imaging findings of SCC and LRC.

Methods This was a retrospective study of patients who underwent staging MRI for anorectal malignancy (<5 cm from the anal verge) for adenocarcinoma or squamous cell carcinoma between 2016 and 2021. Two radiologists blinded to biopsy reviewed MRI. Imaging findings and apparent diffusion coefficient (ADC) values were compared between SCC and LRC.

Results We studied 137 patients (n = 60 SCC, n = 77 LRC) with a mean age of 50.4 (standard deviation: 12.4) years and tumor length of 5.6 ± 1.9 cm. SCC patients were older, and their distal tumor margin was closer to the anal verge (5.3 vs. 22 mm for LRC; p <0.001). T2 intermediate signal and diffusion restriction was seen in 97 and 98.2% of SCC and 75.3 and 77% of LRC, respectively. SCC had lower ADC values (0.910 × 10⁻³ mm²/s) than LRC (1.126 × 10⁻³ mm²/s; p < 0.001). But there was no difference in the ADC values when T2 hyperintense tumors were excluded (p = 0.132). Extramural vascular invasion (EMVI) was more frequent in LRC (35.1 vs. 16.7%; p = 0.013). A combination of distance from the anal verge of less than 11 mm, absent EMVI, and the presence of internal iliac and inguinal nodes had an area under the curve (95% confidence interval) of 0.810 (0.737–0.884).

Conclusion ADC values are unhelpful in differentiating SCC and LRC. Tumors closer to anal verge, absence of EMVI, and the presence of inguinal and internal-iliac nodes may point towards SCC.

Keywords

squamous cell carcinoma - low rectal cancer - adenocarcinoma - anorectal malignancy - anal cancer - MRI

Abbreviation

LRC – low rectal cancer

SCC – squamous cell carcinoma

CRT – chemoradiotherapy

APE - abdominoperineal excision

ELAPE - extra-levator APE

TME – total mesorectal excision

p-CRM - pathological CRM

MMC - mitomycin C (MMC) and

5-FU - 5-fluorouracil

Ethical Approval and Consent to Participate

Institutional Review Board approval was obtained. IRB Min No. 14621, 27.04.2022. Written informed consent was waived by the Institutional Review Board.

Availability of Data and Materials

The datasets generated and/or analyzed during the current study are not publicly available due to institutional data protection policies but are available from the corresponding author on reasonable request.

Authors' Contributions

Anuradha Chandramohan conceptualized and designed the study. Anuradha Chandramohan, Kirthi Sathyakumar, and Antony Augustine contributed to literature research and manuscript preparation. Anuradha Chandramohan, Kirthi Sathyakumar, Antony Augustine, Mark Rajan Jesudason, Rohin Mittal, Jeba Karunya, Thomas S. Ram, and Ashish Singh helped in clinical studies. Reka K was involved experimental studies/data analysis and statistical analysis. Anuradha Chandramohan, Kirthi Sathyakumar, Antony Augustine, Reetu John, Betty Simon, Rijo Issac, Dipti Masih, Jeba Karunya, Thomas S Ram, Ashish Singh, Mark R Jesudason, and Rohin Mittal edited the manuscript. Anuradha Chandramohan and Rohin Mittal are guarantor of integrity of the entire study.

Publication History

Article published online:
24 April 2023

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