What imaging modalities are recommended to monitor kidneys with probable cysts detected on Computed Tomography (CT) scan?

From the Guidelines

For kidney cysts detected on CT scan, follow-up imaging with ultrasound in 6-12 months is recommended to monitor the cysts for stability. Simple renal cysts are common, benign fluid-filled structures that typically require no treatment unless they cause symptoms or show concerning features. If the cysts appear simple (round, thin-walled, fluid-filled without internal structures), they generally don't require intervention. However, complex cysts with irregular walls, calcifications, or solid components may need more frequent monitoring or evaluation by a urologist. Symptoms requiring medical attention include flank pain, hematuria, or signs of infection. No medications are typically prescribed for asymptomatic simple renal cysts. The follow-up interval may be adjusted based on the specific characteristics of the cysts, their size, and whether they're growing. Ultrasound is preferred for follow-up due to lack of radiation exposure, though CT or MRI might be used in certain cases for better characterization, as noted by 1.

According to 1, three modalities can be used for kidney imaging: ultrasound, CT, and MRI, with ultrasound being a good option for initial follow-up due to its lack of radiation. However, CT and MRI can provide more precise lesion measurements, especially for coalescent lesions. It's also important to consider the patient's age, body habitus, and other factors when choosing an imaging modality. For example, ultrasound may be less accurate in patients with large body habitus, while CT and MRI can provide better imaging in these cases.

In terms of specific guidelines, 1 recommends that the growth of kidney masses is assessed using the same imaging modality, which can help ensure consistent and accurate measurements. Additionally, 1 provides guidance on the evaluation of indeterminate renal masses, including the use of CT and MRI with intravenous contrast and a dedicated multiphase protocol. However, for simple renal cysts, a more conservative approach with ultrasound follow-up may be sufficient, as suggested by the lack of strong evidence for more intensive monitoring or treatment.

Key points to consider when monitoring kidney cysts include:

• The size and characteristics of the cysts
• The presence of symptoms such as flank pain, hematuria, or signs of infection
• The patient's age and body habitus
• The need for consistent imaging modality to assess growth or changes in the cysts
• The potential risks and benefits of different imaging modalities, including radiation exposure and accuracy.

From the Research

Imaging Modalities for Monitoring Kidney Abnormalities

• Ultrasound, CT scan, and MRI are the main imaging modalities used to monitor kidney abnormalities, including probable cysts 2.
• CT scan is the mainstay of renal imaging, provided that standardized injection protocols are used and renal function is assessed 2.
• MRI provides anatomic and functional information, but severe renal failure is a contraindication to both CT scan and MRI 2.

Diagnosis and Management of Complex Renal Cysts

• The Bosniak classification is a valuable tool for clinicians to diagnose and manage complex renal cysts 3.
• Computed tomography remains the gold standard for diagnosing complex renal cysts, but newer diagnostic imaging modalities such as contrast-enhanced ultrasonography are demonstrating promising results 3.
• Percutaneous biopsy of complex lesions is well tolerated and adequate for diagnosis, but current apprehension with regard to iatrogenic complications may be exaggerated 3.

Imaging Approaches for Polycystic Kidney Disease

• Imaging is an important approach to diagnosis, monitoring, and predicting outcomes for patients with autosomal-dominant polycystic kidney disease 4.
• Total kidney volume, as measured by magnetic resonance imaging, is suggested as an important potential marker to determine disease progression and overall prognosis 4.
• Renal blood flow and a novel approach to interpreting noncystic renal parenchyma by computed tomography images are other innovative imaging approaches described 4.

Role of ACE Inhibitors in Renal Cyst Growth

• The therapeutic benefit of angiotensin converting enzyme inhibition (ACEI) in diminishing the renal cyst growth, treatment of the hypertension, and reversing the increased left ventricular mass in ADPKD is supportive of the potential pathogenetic role of the renin-angiotensin-aldosterone system (RAAS) in the renal cyst growth 5, 6.
• ACE inhibitors have a greater effect on lowering urine protein excretion and slowing kidney disease progression in patients with higher levels of baseline urine protein excretion 6.