Locally Recurrent Rectal Cancer in the Lateral Compartment: Imaging Features and Association with Primary Tumour Characteristics

Background and Purpose Locally recurrent rectal cancer (LRRC) involving the lateral pelvic compartment is associated with a poor prognosis. The underlying aetiology, such as lateral lymph node(s) (LLN) metastases or other high-risk features, remains unclear. This study aimed to investigate features of lateral LRRC and their anatomical association with primary tumour characteristics. Methods All patients with lateral LRRC referred to our centre between 2018 and 2025 were included ( n = 104). Primary and recurrent tumour MRIs were centrally re-reviewed to evaluate tumour features. An expert panel further assessed anatomical relationships between the primary tumour locations and lateral LRRC sites. Primary outcome was to characterise recurrence features; secondary outcomes were overall and local re-recurrence-free survival. Results Primary tumours of 104 patients frequently showed a high prevalence of high-risk radiological features: extramural vascular invasion (45%), cT3cd–cT4ab staging (47%), tumour deposits (23%) and pathological LLNs (≥ 7 mm short axis, LLN+, 20%). In patients with LLN+ primary tumours ( n = 21), the incidence of the other synchronous high-risk features was significantly increased. Within this group, primary LLN dissection (LLND) was performed in 7/21 (33%). Subsequent lateral LRRC due to LLN nodal recurrence occurred in 10/21 (48%), including 4 patients who had undergone LLND. Overall, the expert panel linked 11% of lateral LRRC to LLNs visible on primary imaging, and the remaining 89% to other causes. Conclusions Only a minority of lateral LRRCs could be attributed to primary LLN+. Other causes, related to primary tumour spread and high-risk features, appear to be associated with the majority of lateral LRRC, suggesting a multifactorial aetiology.