To explore the causes of missed diagnosis of small renal masses (SRM) by ultrasound.

A total of 917 patients with SRM underwent resection at Shanxi Province Cancer Hospital from January 2013 to September 2022 and had complete medical records, in which 25 cases of SRM missed by ultrasound (missed group) and 50 cases of SRM accurately detected by ultrasound (detection group) were included in this study. The differences in sex, age, and body mass index (BMI) between the two groups were compared. Taking the anatomical position of lesions on CT imaging as the standard, the differences in nodule size, laterality, polarity, location, and growth pattern were compared between the two groups. The ultrasonic manifestations and pathological types of the lesions were summarized. The tumor size of the two groups, with a skewed distribution, was compared by the Mann-Whitney U test. The comparison of categorical variables between the two groups was performed using the χ² test or Fisher's exact test.

The missed diagnosis rate of SRM by ultrasound was 2.7% (25/917). Compared with the non-missed group, patients of the missed group were more likely to be obese (44.0% vs 18.0%, Z=-3.793, P<0.001), had small-sized lesions [2.05 (1.47, 2.70) cm vs 2.90 (2.27, 3.52) cm, χ²=6.171, P=0.046], had a high proportion of ≤ 2.5 cm SRM (73.1% vs 26.0%, χ²=9.412, P=0.002), and lesions with deep location (dorsal or medial) (76.9% vs 52.0%, χ²=4.447, P=0.035), and had a high proportion of endophytic masses (26.9% vs 0, χ²=13.946, P=0.001).

Factors such as obesity, tumor size especially ≤ 2.5 cm, deep location, and endophytic growth pattern may interfere with US examination, thus leading to missed diagnosis. When performing renal ultrasound examination, anatomical factors of the lesion should be fully considered to reduce missed diagnosis.