Altered renal corticomedullary differentiation on CT, Part I: A pictorial review of non-neoplastic causes.

The renal corticomedullary interface represents a physiologic differentiation in perfusion between the highly vascular cortex and the medulla. On computed tomography (CT), the corticomedullary phase (CMP), typically acquired 25-35 s after contrast administration, provides an optimal window for evaluating these perfusion differences during the early phase of contrast enhancement. Although often discussed in the context of neoplastic disease, the loss of corticomedullary differentiation (CMD) most commonly occurs across a variety of nonmalignant processes and can serve as an early indicator of underlying renal pathology, including vascular insults, infectious etiologies, functional disturbances related to acute kidney injury, and fibrotic or infiltrative processes seen in chronic kidney disease. A structured approach to evaluating CMD, recognizing characteristic enhancement patterns of pathology, and correlating them with clinical context can enable radiologists to differentiate among the most common presentations. In this pictorial review, we illustrate the normal appearance and enhancement dynamics of the CMP and highlight characteristic imaging patterns of CMD loss across key nonmalignant entities. These imaging patterns underscore the sensitivity of altered CMD in detecting renal pathologies and may improve diagnostic confidence and guide timely clinical management.