Epidemiology and stone localization
Urolithiasis affects 3% to 5% of the population. Statistically, the disease is more common in men than in women, with a peak prevalence occurring under the age of 60. The pathology is diagnosed significantly more often in adults than in children, and Caucasians are affected more frequently than individuals of African descent.
Anatomically, there are three typical sites of stone impaction along the urinary tract:
- Ureteropelvic junction (ureteropelvic junction).
- The site where the ureter crosses the iliac vessels.
- Vesicoureteric junction (vesicoureteric junction).
Determining the exact size of the calculus is of paramount importance for choosing the treatment strategy. If the stone size does not exceed 5 mm, the probability of its spontaneous passage is considered very high. With a diameter greater than 10 mm, the chances of spontaneous passage are extremely low.
Pathogenesis of pain syndrome (Renal colic)
The flank region is the anatomical area between the pelvis and the ribs, located lateral to the spine. The kidneys and ureters receive visceral innervation from spinal cord segments T10–L1 and T11–L1. Pathology of these organs results in referred pain transmitted via somatic fibers to the corresponding dermatomes.
Pain in nephrology and urology is generated through three main mechanisms:
- Stretching of the renal capsule: causes dull, aching, and constant pain (e.g., in inflammatory edema or venous congestion). An exception is renal infarction, which causes sharp pain due to acute stretching.
- Inflammatory mucosal edema and pelvic distension: produces intense, progressive pain (characteristic of pyelonephritis).
- Smooth muscle spasm: occurs during urinary tract obstruction by a stone. This exact mechanism underlies renal colic — an acute, highly intense, paroxysmal pain localized in the flank and radiating along the course of the ureter.
Voiding dysfunction in urolithiasis
The presence of calculi may be accompanied by various disturbances in the rhythm and pattern of urination (dysuria). Symptoms depend on the location of the stone and involvement of adjacent structures:
- Pollakiuria (frequent urination). If the symptom worsens during daytime hours and with physical activity, it is a pathognomonic sign of bladder stones.
- Urinary incontinence (urge incontinence). Unlike true incontinence, in this condition the patient experiences an urge, but due to acute irritation of bladder receptors by the stone, they are physically unable to hold urine until the onset of micturition.
- Stranguria (painful, difficult urination with burning/tenesmus). If the calculus causes secondary cystitis, maximum pain will be observed at the very end of urination upon contraction of the inflamed bladder wall.
Diagnostic Radiology and Differential Diagnosis
The ideal imaging method should provide accurate information in a single test regarding the presence of stones, their size, location, and complications (e.g., obstruction).
According to the American College of Radiology (ACR) guidelines, the first-line method for acute flank pain and clinical suspicion of urolithiasis is non-contrast low-dose CT of the abdomen and pelvis (stone protocol CT). This method has high sensitivity (95–96%) and specificity (98%).
The role of MRI in stone detection is limited due to the method's low sensitivity to calcified structures. MR urography is used only in specific situations, such as evaluating pregnant women or following initial CT.
Because the symptoms of urolithiasis are often nonspecific, CT also helps perform a differential diagnosis with other causes of acute flank pain:
- Urological: blood clots, collecting system tumors, acute pyelonephritis, pyonephrosis.
- Non-urological: biliary colic, acute cholecystitis, leaking abdominal aortic aneurysm, pneumonia, myocardial infarction, testicular or ovarian torsion, ectopic pregnancy, appendicitis, omental infarction, and inflammatory bowel disease.
The three typical sites of stone impaction can be easily remembered by the mnemonic: Ureteropelvic junction, Crossing with iliac vessels, Vesicoureteric junction.
Class and exam questions
What determines the probability of spontaneous stone passage?
Calculus size is of fundamental importance. Stones 5 mm and smaller pass with a very high probability, whereas with a size greater than 10 mm, spontaneous passage is unlikely.
Which diagnostic imaging method is the gold standard for renal colic?
The first-line method is non-contrast low-dose computed tomography (CT) of the abdomen and pelvis. It detects stones with a sensitivity of up to 96%.
How to differentiate pain from a bladder stone from other types of pollakiuria?
When bladder stones are present, frequent urination has a clear relationship with physical activity — symptoms noticeably worsen during the day and with movement.
Why is MRI not used as the primary method for stone detection?
The main limitation of magnetic resonance imaging is its low sensitivity to calcified structures. MRI is reserved for special clinical situations, such as in pregnant patients.
What else to study on this topic
- Types of urinary incontinence: differential diagnosis of true, false incontinence, and enuresis.
- Mechanisms of pain syndrome formation during renal capsule stretching and inflammatory edema.
- Imaging in renal tumor screening: transitional cell carcinoma and the role of contrast enhancement.
- Diagnostic imaging algorithm in renal trauma and iatrogenic hematuria.
- Causes of chronic flank pain: from tuberculosis to gastrointestinal neoplasms.
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