The renal parenchyma is the functional tissue of the kidney, consisting of the outer cortex (where blood is filtered to form urine) and the inner medulla (which concentrates urine). On ultrasound, the renal cortex normally appears slightly less echogenic (slightly darker) than the liver and spleen, and the medullary pyramids appear as darker, triangular structures within the cortex. Sonographers assess the parenchyma for thickness, echogenicity, and any focal abnormalities. Increased echogenicity of the renal parenchyma (appearing brighter than normal, approaching or exceeding liver echogenicity) is a non-specific but important finding that can indicate chronic kidney disease, nephritis, or other diffuse renal processes. Thinning of the parenchyma suggests chronic damage or obstruction.