Kidney stones are solid masses formed from crystallized minerals and salts within the urinary tract. These deposits, often composed of calcium oxalate or uric acid, develop in the kidney and may travel down the narrow tubes leading to the bladder. A 6-millimeter (mm) stone sits in a challenging, borderline category for spontaneous passage. This information is for general health knowledge only; consult your physician regarding your specific condition.
Likelihood of Natural Passage
A 6mm kidney stone sits at a threshold size where the chances of passing it without medical intervention begin to decrease significantly. For stones smaller than 4mm, the probability of natural passage is high, often exceeding 80%. However, when the stone reaches the 6mm diameter, the likelihood of spontaneous passage typically falls below 50%.
The main obstacle to passage is the ureter, the tube connecting the kidney to the bladder, which is narrow and can constrict around a stone of this size. The stone’s exact location within the ureter is a major determinant of success. Stones that have already descended to the lower third of the ureter, closer to the bladder, have a considerably better chance of passing than those lodged in the upper ureter near the kidney.
The shape of the stone also plays a role, as smooth stones move more easily than those with jagged edges. While the average time for a smaller stone to pass is around a month, a 6mm stone may take several weeks or even a few months to navigate the urinary tract. If the stone remains lodged for too long, it can cause complications like obstruction, which prevents urine flow and may damage the kidney.
Managing the Stone Passage Experience
For medically stable patients whose 6mm stone is deemed likely to pass, conservative management focuses on supportive care. This involves ensuring maximum hydration to increase urine volume, which helps flush the stone downward through the ureter. Physicians recommend consuming enough fluids to maintain a light-colored urine output.
Medical expulsive therapy (MET) is frequently used to assist the process, often involving alpha-blockers like tamsulosin. These medications relax the smooth muscles in the ureter wall, widening the tube to facilitate the stone’s movement. These drugs are typically taken for several weeks while the patient waits for passage.
Pain management is a central component, as stone movement often causes intense, colicky flank pain. Non-steroidal anti-inflammatory drugs (NSAIDs) are often prescribed to manage discomfort and reduce swelling in the ureter. Patients must strain all urine using a collection device to capture the stone once it passes. Collecting the stone allows for laboratory analysis of its mineral composition, which is vital for preventing future stone formation.
Patients under conservative management must be alert for specific warning signs that signal a complication requiring immediate medical attention. These include fever or chills, which can indicate a urinary tract infection behind the stone blockage. Other urgent signs are intractable pain that cannot be managed with prescribed medication or a complete inability to urinate. These symptoms suggest a severe obstruction or infection necessitating prompt intervention.
Treatment Options When the Stone Will Not Pass
When a 6mm stone fails to pass after conservative management, or if it causes complications like persistent obstruction or infection, interventional treatment is required. The two most common minimally invasive procedures for stones of this size are Shock Wave Lithotripsy (SWL) and Ureteroscopy (URS). The choice depends on the stone’s location and hardness.
Shock Wave Lithotripsy is a non-invasive technique that uses focused high-energy sound waves delivered from outside the body to break the stone into tiny, sand-like fragments. These small pieces can then be passed naturally in the urine. SWL is generally an outpatient procedure and is best suited for stones located in the kidney or upper ureter.
Ureteroscopy involves passing a small, flexible telescope through the urethra and bladder into the ureter to visualize the stone directly. Once the stone is located, instruments can be used to either retrieve it intact or use a laser to break it into smaller fragments (laser lithotripsy). URS is effective for stones in any location of the ureter and may be preferred if the stone is particularly hard or if the patient has an infection. Both procedures aim to remove the blockage and prevent potential long-term damage to the kidney function.