A ureteral calculus is a hard, solid mass that originates as a kidney stone but has traveled from the kidney and become lodged within the ureter. The ureter is a narrow, muscular tube connecting the kidney to the bladder to transport urine. When a calculus moves into this passageway, it can partially or completely block the flow of urine. This obstruction causes the condition’s characteristic and severe symptoms.
How Ureteral Calculi Develop
Calculi form when the urine becomes oversaturated with certain minerals and salts, a process that leads to crystallization. The urinary system normally keeps these substances diluted, but an imbalance causes them to clump together, forming a hard mass. Approximately 80% of all stones are composed of calcium, most often in the form of calcium oxalate or calcium phosphate crystals.
The primary mechanism for stone formation involves a lack of sufficient fluid intake, which results in a low volume of urine with a high concentration of stone-forming substances. When the urine is highly concentrated, the crystallization process is encouraged. Aside from low fluid intake, a high dietary intake of sodium and animal protein can also increase the risk of stone formation.
Certain dietary components affect the risk, such as high oxalate intake from foods like spinach, nuts, and chocolate. A family history of stones also suggests a genetic predisposition, and individuals with a history of recurrent urinary tract infections can develop struvite stones, which are composed of magnesium ammonium phosphate.
Recognizing the Symptoms
The most recognizable symptom of a ureteral calculus is acute renal colic, a sudden and excruciating pain. This pain is not constant but comes and goes in waves, which is caused by the ureter’s muscular walls contracting in an attempt to push the stone through the tube. The severity of the pain is directly related to the degree of obstruction and the subsequent stretching of the kidney’s capsule, not the size of the stone itself.
The pain typically begins in the flank or side, just below the ribs, and radiates downward as the stone moves along the ureter. As the calculus descends, the pain may shift toward the abdomen, groin, or even the testicle in men or the labia in women. This intense discomfort is frequently accompanied by secondary symptoms such as nausea and vomiting, which are triggered by the shared nerve pathways between the kidneys and the digestive tract.
As the stone nears the bladder, it can cause lower urinary tract symptoms, including a frequent and urgent need to urinate, as well as a burning sensation during urination. Blood in the urine, known as hematuria, is also a common finding, which results from the stone irritating the lining of the urinary tract. The presence of these dramatic symptoms generally warrants immediate medical attention.
Diagnosis and Treatment
Diagnosing a ureteral calculus begins with a focused history and physical examination, but definitive confirmation relies on medical imaging. Non-contrast computed tomography (CT) is the preferred imaging method because of its high sensitivity and specificity in visualizing stones and identifying any associated urinary tract obstruction. A urinalysis is also routinely performed to check for blood, infection, or microscopic crystals in the urine.
Treatment depends on the stone’s size, location, and the presence of any complications like infection or severe obstruction. Small stones, typically those under 5 millimeters in diameter, have a high probability of passing spontaneously and are often managed with observation, pain medication, and increased fluid intake. Medical Expulsive Therapy (MET) may be used, which involves prescribing alpha-blockers, such as tamsulosin, to help relax the ureter’s muscle and facilitate the stone’s passage.
For larger stones, those that fail to pass, or those causing a severe blockage, more active intervention is necessary. Extracorporeal Shock Wave Lithotripsy (SWL) is a non-invasive procedure that uses focused sound waves delivered from outside the body to break the stone into smaller fragments that can be passed naturally. Alternatively, Ureteroscopy (URS) is a minimally invasive surgical procedure where a small, flexible scope is passed through the urethra and bladder into the ureter to either remove the stone directly using a basket or fragment it with a laser.