From the Guidelines
Radiolucent kidney stones are primarily composed of uric acid, which are typically radiolucent and can be distinguished from other types of stones by their lower computed tomography attenuation values 1. The most common type of radiolucent kidney stone is uric acid stones, which can be identified by their low attenuation or radiolucent appearance on imaging, particularly in patients with a low urinary pH 1. Some key characteristics of uric acid stones include:
- Lower computed tomography attenuation values compared to calcium, cystine, and struvite calculi 1
- Typically form in acidic urine (pH below 5.5) due to high uric acid concentration
- Can be managed with manipulation of the urinary pH using oral potassium citrate, sodium citrate, or sodium bicarbonate to a level ranging from 6.0 to 7.0, which may obviate the need for surgical intervention 1 Other types of radiolucent kidney stones, such as xanthine or drug-induced stones, are less common and may require different management approaches. Non-contrast CT scans are the preferred diagnostic method for identifying radiolucent stones, as they do not appear on standard X-rays. Management of radiolucent kidney stones typically involves increasing fluid intake, urinary alkalinization, dietary modifications, and sometimes medications to reduce uric acid production in recurrent cases.
From the Research
Types of Radiolucent Kidney Stones
- Uric acid stones: These are the most common type of radiolucent kidney stones, accounting for approximately 10% of all kidney stones 2, 3, 4.
- Cystine stones: These are less common, accounting for approximately 0.6% of all kidney stones 4.
- Other radiolucent stones: These may include stones composed of other salts, but are less common than uric acid or cystine stones 4.
Characteristics of Radiolucent Kidney Stones
- Uric acid stones are often associated with low urine pH and hyperuricosuria 2, 3, 4.
- Cystine stones are often associated with cystinuria, a genetic disorder that affects the kidneys' ability to reabsorb cystine 5.
- Radiolucent stones may be more difficult to detect on X-ray, requiring alternative imaging modalities such as ultrasonography or computed tomography scans 2, 6.
Treatment of Radiolucent Kidney Stones
- Medical dissolution therapy: This involves the use of oral medications such as potassium citrate to alkalize the urine and promote stone dissolution 2, 3, 5, 6.
- Factors affecting response to treatment: Stone size, density, and location may affect the success of medical dissolution therapy, with smaller, less dense stones being more likely to respond to treatment 6.