What is a calyceal diverticulum?

What is a Calyceal Diverticulum?

A calyceal diverticulum is a rare, congenital outpouching of the renal collecting system—specifically a cystic cavity within the kidney parenchyma that is lined with transitional cell epithelium and communicates with the calyx or renal pelvis through a narrow neck. 1, 2

Pathogenesis and Origin

• Calyceal diverticula are thought to have a congenital origin, arising from abnormalities during ureteral bud formation and development of the collecting system 2, 3
• The more accurate term would be "pyelocalyceal diverticulum" since the connection can be to either the calyces or the renal pelvis 3
• These are distinct from simple renal cysts because they maintain communication with the collecting system and contain urine rather than simple fluid 4

Clinical Presentation

• Most calyceal diverticula follow an asymptomatic course and rarely require medical intervention 2
• When symptomatic, presentations typically relate to:
  • Stone formation (found in up to 50% of diverticula, though 96% of symptomatic patients present with stones) 1
  • Obstruction to drainage of the diverticulum 2
  • Secondary infection 2
  • Large size causing mass effect 2
• Pain in the lumbar region is a common complaint when symptoms develop 4

Diagnostic Approach

Initial Imaging Considerations

• Calyceal diverticula are frequently underdiagnosed on ultrasonography because they can be mistaken for simple renal cysts 3
• Ultrasonographic findings should raise suspicion, but definitive diagnosis requires contrast-enhanced imaging 5, 3

Definitive Diagnostic Modalities

• CT urography (CTU) with excretory phase imaging is the primary diagnostic test, providing detailed anatomic depiction of the collecting system and demonstrating the communication between the diverticulum and collecting system 6, 5
• Excretory-phase MRI or MR urography can confirm the diagnosis and is particularly useful in pediatric patients to avoid radiation 3
• Delayed intravenous pyelography can demonstrate the narrow infundibular connection 4
• Retrograde pyelography may be employed when other modalities are inconclusive 4

Diagnostic Confirmation Techniques

• If imaging is equivocal, percutaneous aspiration of cyst fluid with creatinine measurement can confirm the diagnosis: creatinine levels significantly higher than simultaneous serum creatinine indicate the fluid is urine, confirming communication with the collecting system 4
• Intravenous injection of methylene blue through a ureteral catheter can aid visualization during procedures 4

Key Diagnostic Pitfalls

• The narrow neck connecting the diverticulum to the collecting system may not be visible on all imaging phases, requiring delayed excretory imaging to demonstrate opacification 6, 3
• Simple cysts do not communicate with the collecting system and will not opacify with contrast, distinguishing them from calyceal diverticula 3
• In pediatric patients especially, the diagnosis requires a high index of suspicion as these lesions are very rare in children 3

Clinical Significance

• While benign in the vast majority of cases, rare instances of malignancy arising from calyceal diverticula have been reported 2
• The presence of stones within diverticula increases the likelihood of symptoms and need for intervention 1
• Metabolic disturbances have been identified in patients with calyceal diverticular stones, which may provide insights into the underlying pathology 5