Pelvicalyceal System Anatomy
Overview
The pelvicalyceal system is the renal collecting system composed of minor calyces, major calyces (infundibula), the renal pelvis, and the ureteropelvic junction (UPJ), which collectively drain urine from the renal papillae to the ureter. 1
Structural Components
Minor Calyces
- Minor calyces are cup-shaped structures that surround the renal papillae and represent the first collecting point for urine in the kidney 1
- The number and orientation of minor calyces varies considerably between individuals and even between kidneys in the same person 2
- Minor calyces drain into larger collecting structures called major calyces or infundibula 1
Major Calyces (Infundibula)
- Major calyces are formed by the convergence of multiple minor calyces and serve as intermediate collecting channels 1
- The infundibulum refers specifically to the stem or neck of a major calyx that connects it to the renal pelvis 3
- Infundibular length of the lower pole is clinically significant: lengths >30mm (found in 9.7-61% of kidneys) can impair stone clearance after lithotripsy procedures 4, 3
- Infundibulopelvic angle (the angle between the infundibulum and renal pelvis) varies widely; angles <70° occur in approximately 43% of kidneys and may affect surgical outcomes 3
Renal Pelvis
- The renal pelvis is the funnel-shaped expansion where major calyces converge before draining into the ureter 1
- Intrarenal pelvis (narrow, funnel-shaped, located within the renal sinus) occurs in 48.5-78% of kidneys 1, 3
- Extrarenal pelvis (dilated, balloon-shaped, extending beyond the renal sinus) occurs in 6.1-21.9% of kidneys and may predispose to urinary stasis and stone formation 1, 3
- Borderline/partially intrarenal pelvis occurs in 13.4-20.9% of kidneys 1, 3
- The pelvicalyceal surface area averages 20-25 cm² and affects surgical stone clearance rates 5
Ureteropelvic Junction (UPJ)
- The UPJ is the transition point where the renal pelvis narrows to become the ureter 6
- The cross-sectional area of the UPJ relative to the renal pelvis influences urinary drainage 6
Classification Systems
Calyceal Pattern Classification
- Bicalyceal system (32.9%): Two major calyces drain into the pelvis 3
- Tricalyceal system (26.8%): Three major calyces (upper, middle, lower poles) 3
- Multicalyceal system (20.7%): More than three major calyces 3
Modified Takazawa Classification (Based on 3D Reconstruction)
- Type A (62%): Single pelvis without bifurcated branches 6
- Type B (38%): Divided pelvis with bifurcated branches 6
Clinical Significance
Stone Disease Management
- Pelvicalyceal surface area <20.5 cm² is associated with higher percutaneous nephrolithotomy (PCNL) success rates (78.1% overall success) 5
- Extrarenal pelvis predisposes to urinary stasis and stone formation due to the dilated, balloon-shaped configuration 1
- Lower pole infundibular length >22-30mm significantly reduces stone clearance after shock wave lithotripsy 4, 3
Imaging for Renal Aspergillosis
- Nephrostomy with amphotericin B lavage of the pelvicalyceal system may be required for fungal balls, as systemic antifungals do not achieve adequate concentrations in the renal pelvis or urine 4
Anatomical Variability
- Bilateral symmetry of pelvicalyceal anatomy occurs in only 27.1% of individuals, meaning most people have different collecting system configurations between their kidneys 1
- Classification systems remain inconsistent despite over a century of study, with significant gaps in correlating anatomy with modern minimally invasive interventions 2
Common Pitfalls
- Underestimating anatomical complexity: The pelvicalyceal system shows extreme individual variation that cannot be predicted from external kidney appearance 2, 1
- Assuming bilateral symmetry: Most patients have asymmetric collecting systems between kidneys 1
- Ignoring lower pole anatomy: Unfavorable lower pole infundibular length and angle significantly impact stone treatment outcomes 3, 5