Subcapsular beaded appearance of the kidney on contrast-enhanced CT: indicative of dilated subcapsular lymphatics?

To assess the renal subcapsular beaded appearance (RSBA) seen on contrast-enhanced multidetector-row computed tomography (CT).

In total, 2,020 consecutive MDCT examinations with both non-contrast-enhanced and contrast-enhanced procedures were assessed retrospectively to identify interconnecting lobular structures in the renal subcapsular area that created a beaded appearance on contrast-enhanced CT. Positive cases were investigated for CT attenuation on unenhanced CT and were then compared with fat-suppressed heavily T2-weighted magnetic resonance imaging (MRI) and follow-up CT if available. The degree of RSBA occupying the renal periphery was evaluated using a three-grade system (Grade I: <25%, Grade II: 25-75%, Grade III: >75% of surface involvement). Only Grades II and III were defined as a positive RSBA. Possible associated findings such as hypertension, chronic kidney disease (CKD), renal atrophy, and liver cirrhosis were also evaluated.

The RSBA was positive in 33 (1.63%) of patients and was more commonly found in patients in their seventies (39.4%) with male predominance (male:female ratio, 7:3; p=0.005). Of 33 positive cases, five showed low CT attenuation predominance, 25 showed iso-attenuation, and three showed high attenuation on unenhanced CT. In five positive cases, T2-weighted MRI showed markedly high signal intensity, suggesting prominent capsular lymphatic structures. The RSBA was associated with hypertension (p=0.001) and CKD (p=0.011).

The MRI findings suggested that the RSBA probably reflects dilated subcapsular lymphatics. Knowledge of this CT finding is clinically important because it might be misinterpreted as other pathological findings.