How to differentiate between calyceal diverticula and choked calyx pre-operatively on the left side?

Differentiating Calyceal Diverticula from Choked Calyx Pre-operatively

The key to differentiating calyceal diverticula from choked calyx pre-operatively is demonstrating communication with the collecting system through contrast-enhanced imaging, specifically CT urography or retrograde pyelography, which will show a narrow neck connecting the diverticulum to the calyx, while a choked calyx shows obstruction at the infundibulum with proximal calyceal dilation but no discrete outpouching. 1, 2

Primary Diagnostic Approach

CT Urography (First-Line Imaging)

• CT with contrast enhancement is the most accurate imaging modality for diagnosing calyceal diverticula, demonstrating the characteristic smooth-walled, urine-filled cavity that communicates with the collecting system through a narrow neck 1, 2, 3
• Delayed phase imaging is critical—perform imaging at 10-15 minutes post-contrast to allow adequate opacification of the diverticulum through its narrow communication 1, 4
• The diverticulum will fill with contrast material, distinguishing it from simple renal cysts or other non-communicating lesions 5, 2

Key Distinguishing Features on CT

Calyceal Diverticulum:

• Smooth-walled, round or oval outpouching that fills with contrast on delayed imaging 1, 2
• Narrow neck (1-5mm) connecting to a calyx, best seen on delayed phases 2, 4
• May contain stones (present in up to 50% of cases) that appear as filling defects 2, 3
• The surrounding renal parenchyma is typically normal unless complicated by infection 5

Choked Calyx:

• Dilated calyx with blunted appearance due to infundibular obstruction 2
• No discrete outpouching separate from the calyx itself
• Obstruction at the infundibular level with proximal calyceal dilation
• May show parenchymal thinning over the dilated calyx

Alternative Diagnostic Modalities

Retrograde Pyelography

• Use retrograde pyelography when CT findings are equivocal or when you need definitive demonstration of the diverticular neck 1, 4
• This provides superior anatomic detail of the collecting system and can definitively show the narrow communication between diverticulum and calyx 1, 2
• Particularly useful for surgical planning as it clearly delineates the neck location and caliber 4

Intravenous Urography (IVU)

• Delayed films (30-60 minutes post-contrast) are essential to allow filling of the diverticulum through its narrow neck 1, 4
• Historical gold standard but now largely replaced by CT urography due to superior anatomic detail 2, 3

MRI Urography

• Fluid-sensitive MRI sequences (T2-weighted) can delineate calyceal diverticula without radiation exposure, making this ideal for young patients or pregnant women 4
• MR urography with gadolinium provides excellent anatomic detail comparable to CT 4

Confirmatory Diagnostic Techniques

Percutaneous Aspiration with Creatinine Analysis

• If imaging remains inconclusive, percutaneous aspiration of the suspected diverticulum with creatinine measurement provides definitive diagnosis 1
• Fluid creatinine significantly higher than serum creatinine confirms the cavity contains urine, diagnostic of calyceal diverticulum 1
• This distinguishes diverticula from simple cysts (which have low creatinine) or other fluid collections 1

Methylene Blue Injection

• Inject methylene blue through a ureteral catheter during cystoscopy—blue dye appearing in the aspirated fluid confirms communication with the collecting system 1
• This technique is particularly useful intra-operatively to confirm the diagnosis before definitive treatment 1

Common Diagnostic Pitfalls

Mimics of Calyceal Diverticula

• Calyceal diverticula can mimic renal tumors, abscesses, or simple cysts on ultrasound, requiring contrast-enhanced imaging for differentiation 5
• Stone-bearing diverticula may be mistaken for renal cell carcinoma or infected cysts on initial imaging 5, 2
• On bone scintigraphy, calyceal diverticula can mimic rib metastases if located in the upper pole 5

Technical Considerations

• Inadequate delay in contrast imaging is the most common reason for missing calyceal diverticula—always obtain delayed phase images 1, 4
• Small diverticular necks (<2mm) may not opacify on standard CT timing, requiring 15-20 minute delayed imaging 2, 4
• Ultrasound alone is insufficient for diagnosis as it cannot reliably demonstrate the communication with the collecting system 5, 4