How should a small (<3 cm) simple renal cyst located at the mid‑pole of the kidney be managed in an otherwise asymptomatic adult with normal renal function?

Management of Small Simple Renal Cysts at the Mid-Pole

A small (<3 cm) simple renal cyst at the mid-pole of the kidney in an asymptomatic adult with normal renal function requires no treatment and no routine imaging follow-up. 1, 2

Initial Characterization

The first step is to confirm that the lesion is truly a simple cyst using imaging criteria:

• On unenhanced CT: Homogeneous masses measuring <20 HU are definitively benign simple cysts and require no further evaluation or urologic referral 1, 2
• On contrast-enhanced CT: Homogeneous lesions measuring 10-20 HU (and recent evidence suggests up to 21-30 HU on portal venous phase) are benign cysts requiring no additional workup 1, 2
• On MRI: Simple cysts demonstrate homogeneous very high T2 signal intensity on unenhanced sequences, which can definitively characterize them without contrast 1

No Surveillance Required

Simple renal cysts (Bosniak I) carry a 0% malignancy risk and do not warrant routine radiologic follow-up or urologic referral 2. The vast majority remain asymptomatic throughout a patient's lifetime and do not require monitoring 3.

When to Reconsider the Diagnosis

You should obtain additional imaging or refer to urology only if:

• The cyst develops any enhancement (>10-15 HU increase on CT or >15% enhancement on MRI), which would reclassify it as a solid or complex mass 2
• The cyst develops septations, wall thickening, nodularity, or calcifications during incidental reimaging, suggesting progression to Bosniak IIF or higher 2
• The patient becomes symptomatic with flank pain, hematuria, or palpable mass directly attributable to the cyst 4, 5

Management of Symptomatic Simple Cysts

If symptoms develop (rare for cysts <3 cm), the management algorithm is:

1. Trial aspiration to confirm the cyst is the pain source—if symptoms resolve temporarily but recur, the cyst is confirmed as symptomatic 5
2. Laparoscopic de-roofing is the definitive treatment, with superior long-term success compared to aspiration with sclerotherapy (100% vs 0% sustained pain relief at 17 months follow-up) 5
3. Avoid sclerotherapy as primary treatment—all patients treated with ethanol sclerotherapy experienced pain recurrence, whereas laparoscopic de-roofing provided durable symptom resolution 5

Critical Pitfall to Avoid

Do not dismiss "complicated variations" of previously simple cysts during incidental reimaging. If a known simple cyst develops wall irregularity, septations, or any solid component on subsequent imaging obtained for unrelated reasons, this carries an extremely high probability of malignancy and requires immediate urologic referral 6. In one cohort, all 31 cases of "complicated variation" of previously documented simple cysts proved to be renal cell carcinoma on pathology 6.

Documentation Recommendation

Document in the radiology report and clinical note that this is a Bosniak I simple cyst requiring no follow-up, to prevent unnecessary repeat imaging and patient anxiety 2.