Sono-graphic Rim Sign in Postpartum Renal Cortical Necrosis: Experience at a Tertiary Care Centre

Kidney biopsy or contrast studies are required to diagnose acute renal cortical necrosis (RCN). Both procedures may be potentially delayed in the postpartum setting. Contrast-enhanced ultrasound (CEUS) is a potential alternative for these patients but remains limited in availability. Due to sparse literature and the rarity of RCN, the role of conventional B-mode ultrasound (USG) in diagnosing RCN remains unexplored.

This retrospective study involved postpartum patients with RCN who underwent kidney biopsy at a tertiary care center. Medical records and B-mode USG kidney images of all 23 patients with postpartum RCN over the past 24 months were retrieved. Gray-scale B-mode USG images of the kidney were assessed for size, presence of sonographic hypoechoic rim, USG kidney timing, echogenicity, and cortico-medullary differentiation.

Among the 23 patients, sonographic hypoechoic rim was observed in 6 patients (26.1%). USG kidney timing ranged from 1.1 to 8 weeks, and kidney length varied from 9.0 to 10.8 cm. There were significant differences in mean USG kidney timing and mean kidney length between patients with and without hypoechoic rim (P= 0.020 and P= 0.036, respectively). The mean USG kidney timing was notably earlier in patients with sonographic rim signs than those without sonographic rim signs (2.5 ± 0.77 weeks and 4.81 ± 2.17 weeks, respectively).

Despite its lower sensitivity, the sonographic rim sign is an important diagnostic feature of postpartum renal cortical necrosis. In point-of-care ultrasonography, it should be looked for early in the disease course, especially in cases of postpartum anuric acute kidney injury.