Is further workup needed for a 4.8cm parapelvic cyst and a 2.2cm simple exophytic cyst on the right kidney?

Management of Parapelvic and Simple Exophytic Renal Cysts

No further workup is needed for these benign renal cysts, as simple renal cysts—regardless of size—have no malignant potential and do not require routine follow-up or surveillance imaging. 1, 2, 3

Initial Characterization and Risk Assessment

The key question is whether these cysts are truly "simple" on imaging:

• Simple cysts are defined by: thin or imperceptible walls, no septations, no calcifications, no solid components, and homogeneous water attenuation (0-20 Hounsfield units on CT) with no enhancement after contrast administration 1, 2

• If already characterized as simple on adequate imaging (contrast-enhanced CT or MRI), the American Urological Association confirms that simple cysts have no malignant potential and require no follow-up regardless of size 1, 3

• The 4.8 cm parapelvic cyst size does not change management for a confirmed simple cyst, as size alone does not indicate malignancy risk in simple cysts 2, 3

When Further Imaging IS Indicated

You need contrast-enhanced imaging if the cysts have not been adequately characterized yet:

• Contrast-enhanced multiphase CT is the preferred modality to definitively characterize these cysts and exclude concerning features like wall thickening, mural nodules, septations, or enhancement 1, 2, 3

• MRI with intravenous contrast is an acceptable alternative, particularly in younger patients or those with contraindications to iodinated contrast 1, 2, 3

• The goal is to apply the Bosniak classification system: Bosniak I (simple cyst) requires no follow-up, while Bosniak II, IIF, III, or IV would require surveillance or intervention 1, 3

Special Considerations for Parapelvic Cysts

Parapelvic cysts warrant slightly more attention than peripheral simple cysts due to their location:

• Rule out urological malignancy: While rare, parapelvic cysts can occasionally be associated with renal pelvic or ureteral cancer, particularly if presenting with hematuria or flank pain 4

• Assess for obstruction: Parapelvic cysts can cause ureteropelvic junction obstruction or hydronephrosis, which may require intervention if symptomatic 5, 6, 7

• Consider genetic disorders: Parapelvic cysts may be an imaging marker for treatable genetic conditions including Fabry disease, autosomal dominant polycystic kidney disease, or tuberous sclerosis complex 8

• Genetic counseling should be offered if the patient is ≤46 years old, has multifocal or bilateral masses, or has family history suggesting familial renal neoplastic syndrome 1, 3

Clinical Algorithm

If these cysts were identified on ultrasound or non-contrast CT:

• Obtain contrast-enhanced CT or MRI to definitively characterize them 1, 2, 3
• If confirmed as Bosniak I (simple), no further workup or follow-up is needed 1, 3

If these cysts were already characterized as simple on contrast-enhanced imaging:

• No further workup is indicated 1, 3
• No surveillance imaging is needed 1, 3

If the patient has symptoms (flank pain, hematuria, hypertension):

• Evaluate for obstruction with diuretic renography or MR urography 5, 6
• Consider urological referral if obstruction is confirmed 5, 6, 7

If the patient is young (≤46 years) or has family history:

• Offer genetic counseling to evaluate for hereditary renal cystic diseases 1, 3, 8

Common Pitfalls to Avoid

• Do not confuse parapelvic cysts with hydronephrosis on ultrasound—contrast-enhanced cross-sectional imaging or diuretic renography can distinguish between them 5, 6

• Do not assume all cysts are simple without proper characterization—enhancement patterns on contrast imaging are essential to exclude Bosniak IIF or higher lesions 1, 2

• Do not perform surveillance imaging on confirmed simple cysts—this represents unnecessary healthcare utilization and patient anxiety without oncologic benefit 1, 3