Optimising pre-operative imaging-surgery intervals for stones

The NICE guidelines for acute ureteric colic recommend diagnostic imaging, definitive management and definitive care within 24 and 48 h of symptoms and 4 weeks of temporisation, respectively. However, the NHS reality is fraught with long waiting times to definitive treatment, further compounded by a progressively increasing stone burden, paucity of on-site lithotripters and a decrease in non-cancer elective theatre sessions during the COVID-19 pandemic. By the time patients attended the elective surgeries, their reference images (RIs) were often significantly out of date. Scant direction exists on what interval between imaging and surgery invalidates the usefulness of the RIs in providing surgical guidance.This study aimed to evaluate the role of imaging-surgery intervals (ISIs) on upper tract stone negative surgery outcomes and derive a cut-off ISI warranting updated images, with a view to improving efficiency and patient safety.

Upper tract stone surgeries were retrospectively assessed. Each renal unit was considered independently in bilateral stones. Cases were grouped into renal/pelvic (referred to as 'RENAL') and URETERIC stones. Data retrieved included the ISI, intra-operative disparity (IOD) between stone-related features on RIs and the surgical findings. Receiver operating curves (ROCs) were used to determine ISI cut-offs more predictive of IODs.

Four hundred and twenty-seven surgeries on 174 (40.7%) RENAL and 253 (59.3%) URETERIC stones were appraised. No stones were found intraoperatively in 52 (12.1%) patients. Longer ISIs were associated with IODs, especially with URETERIC stones (p = 0.011, CI₉₅ 0.63; 4.84). The derived ROC ISI cut-offs beyond which IODs, including negative surgeries, were more likely were 9 weeks for URETERIC (AUC: 63%, CI₉₅ 0.56; 0.70) and 19 weeks (AUC: 58.6%, CI₉₅ 0.50; 0.68) for RENAL stones, respectively.

There is a need to update reference imaging done more than 9 or 19 weeks before surgery for URETERIC and RENAL stones, respectively.