## Identification of Renal Collecting System on CT ### Anatomical Relationships at the Renal Hilum The renal sinus contains the collecting system of the kidney. At the level of the renal hilum, the structures are arranged in a characteristic pattern: **Key Point:** The renal pelvis is the most posterior and medial structure within the renal sinus, located behind the renal vein and medial to the renal artery. ### Structural Hierarchy of the Collecting System The urinary collecting system follows this sequence from proximal to distal: 1. **Minor calyces** — collect urine from individual renal papillae; multiple (usually 8–12) 2. **Major calyces** — formed by convergence of 2–3 minor calyces; typically 2–3 major calyces per kidney 3. **Renal pelvis** — funnel-shaped structure formed by convergence of major calyces; located at the renal hilum 4. **Ureter** — continuation of the renal pelvis; extends from the hilum to the bladder ### CT Anatomy at the Renal Hilum On axial CT imaging at the level of the renal hilum: - The **renal pelvis** is the most prominent collecting structure visible - It is positioned **posterior and medial** within the renal sinus - It lies **behind the renal vein** (which is anterior) - It is **medial to the renal artery** - It is the **largest and most centralized** collecting structure at this level **High-Yield:** The renal pelvis is the only structure that is simultaneously posterior to the vein, medial to the artery, AND within the sinus at the hilum. The minor and major calyces are more peripheral and intraparenchymal. The ureter is distal to the hilum. ### Clinical Correlation **Clinical Pearl:** Hydronephrosis is best assessed by measuring the anteroposterior diameter of the renal pelvis on CT. A dilated renal pelvis (>10 mm) suggests obstruction. [cite:Robbins & Cotran 10e Ch 20] 
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