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Background: Abdominal bulging affects up to one-fourth of patients after flank incision, with half experiencing impaired quality of life. Identifying patients at risk for morbid bulge could improve preventive and supportive care.

Purpose: To characterise muscular changes related to postoperative abdominal bulging and design a visual scoring system to grade bulge on postoperative CT scans

Material and Methods: Patients treated with open partial nephrectomy via a flank incision between 2005 and 2016 at the University Hospital of Ume & aring; were included. Pre- and postoperative CT scans of the first 50 consecutive patients were used to characterise imaging features of the postoperative abdominal wall. From these features, a four-tiered scoring system for abdominal bulge was designed. Two independent observers tested the system on CT scans from the 50 next patients. Inter-rater reliability was assessed using Fleiss' Kappa.

Results: Common features of abdominal bulging were extracted and a four-tier visual score ranging from normal abdominal wall to severe bulge was developed. Among the patients, similar to 70% had a normal abdominal wall, similar to 25% had bulge score 1, similar to 7% score 2, and similar to 1% score 3. Inter-rater agreement was 73.5%, with Fleiss' Kappa 0.44.

Conclusion: Features of bulge were reduced muscle thickness and ipsilateral gravitational slump affecting part or all of the lateral abdominal wall. The proposed scoring system demonstrated only moderate inter-rater reliability in this pilot setting. Further research on postoperative abdominal wall changes is needed before implementing imaging-based assessments in clinical care.