Flank Bulging and Sensory Disturbances After Open Renal Surgery Through Lumbotomy: Clinical Phenotypes and Procedure-Related Associations

Background and Objectives: Flank bulging is a recognized consequence of open renal surgery through a lumbotomy, but its clinical relevance and relationship with postoperative sensory changes are not well defined. We assessed the frequency and clinical burden of postoperative flank bulging, its overlap with sensory disturbances, and procedure-related factors associated with its occurrence. Materials and Methods: We reviewed 407 patients who underwent open renal surgery through a subcostal lumbotomy between 2018 and 2023. Flank bulging was the primary outcome. We also recorded scar hypoesthesia, wider areas of sensory loss, and whether patients found the resulting deformity bothersome. Factors associated with bulging were explored using multivariable logistic regression, with a separate analysis comparing nephron-sparing surgery (NSS) and radical nephrectomy. Results: Flank bulging was found in 88 patients (21.6%). Scar hypoesthesia occurred in 14.0% and more extensive sensory loss in 7.1%. Sensory abnormalities showed a strongly nested clinical pattern: all patients with scar hypoesthesia had flank bulging, and all extended sensory deficits occurred among patients with both bulging and scar hypoesthesia. All patients with scar hypoesthesia also had bulging, while wider sensory loss was seen only when both were present. Among patients for whom this information was available, 52.9% described the bulging as bothersome. It was more common after NSS than after radical nephrectomy (27.0% vs. 16.3%). The difference persisted after adjustment for age and sex (aOR 2.05, 95% CI 1.17–3.59), corresponding to an adjusted absolute risk difference of 11.8 percentage points (95% CI 2.4–20.8). Conclusions: About one in five patients developed flank bulging after open renal surgery through a lumbotomy, and many of those affected found it bothersome. The accompanying sensory changes raise the possibility that nerve injury contributes to this complication, although our data cannot establish the underlying mechanism. The higher rate observed after NSS compared with radical nephrectomy also warrants further study. Prospective assessment with standardized imaging and more detailed operative data may help explain these findings and identify factors that could reduce the risk of postoperative bulging.