Clinical impact of restaging pelvic DWI-MRI and pelvic nodal assessment for squamous cell carcinoma of the anus in the 6-month interval post chemoradiotherapy

Purpose To evaluate the diagnostic performance of diffusion-weighted imaging (DWI) in determining persistent disease and whether persistent diffusion restriction within the anal canal is associated with overall survival, and investigate the accuracy of pelvic lymph node (LN) assessment on 6-month restaging MRI in patients with squamous cell carcinoma of the anus (SCCA). Patients and Methods This retrospective study included patients with SCCA who underwent chemoradiation therapy (CRT) followed by restaging rectal MRI from January 2010–April 2020, with ≥1 year of follow up after CRT. DWI scans were qualitatively evaluated by two junior and two senior abdominal radiologists. The reference standard for anal persistent disease was digital rectal examination/endoscopy and histopathology. Diagnostic performance was estimated using sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV). Survival outcomes were evaluated via Kaplan–Meier analysis, and associations between survival outcomes and DWI status were tested for significance using the log-rank test. LN assessment was performed on DWI and T2-weighted imaging. Results Among 84 patients (mean age, 63±10.2 years; 64/84 (76%) female), 14/84 (17%) had confirmed persistent disease on restaging MRI. Inter-reader agreement on DWI between all four radiologists was moderate (Light's κ=0.553). Overall, DWI had a sensitivity of 71.4%, specificity of 72.1%, PPV of 34.5%, and NPV of 92.5%. Patients with a negative DWI showed better survival than patients with a positive DWI (3-year overall survival of 92% vs 79% and 5-year overall survival of 87% vs 74%), although the difference did not reach statistical significance (p=0.063). All patients with suspicious lymph nodes on restaging MRI (14/14, 100%) showed negative pathology or decreased size during follow-up. Conclusion At 6 months post CRT, DWI showed value in excluding anal persistent disease. Persistent diffusion restriction on DWI was not significantly associated with overall survival. Pelvic nodal assessment on restaging MRI was limited in predicting persistent nodal metastases.