Residency · Residency · Urology
Imaging and Initial Management of Acute Renal Colic
Clinical Presentation
Acute renal colic typically presents with a sudden onset of severe, colicky flank pain that often radiates to the groin, ipsilateral testicle, or labium. The pattern of pain varies depending on the stone's location within the urinary tract. Stones located at the ureteropelvic junction (UPJ) or proximal ureter usually cause flank pain accompanied by costovertebral angle (CVA) tenderness. When stones are situated in the mid-ureter, patients often experience lower abdominal pain. Distal ureter or ureterovesical junction (UVJ) stones tend to produce suprapubic pain along with urinary urgency and frequency. Associated symptoms frequently include nausea, vomiting, and hematuria, with microscopic hematuria present in approximately 85-90% of cases. However, the absence of hematuria does not exclude stone disease, as about 10-15% of patients may lack hematuria. The presence of fever in a patient with an obstructing stone constitutes a urologic emergency, indicating an obstructed infected kidney requiring urgent intervention.
Differential Diagnosis
The differential diagnosis for acute flank pain mimicking renal colic includes pyelonephritis, renal infarction, and musculoskeletal pain. Right-sided pain may raise suspicion for appendicitis, while left-sided pain could suggest diverticulitis. In women, ectopic pregnancy and ovarian torsion must be considered. In older patients with vascular risk factors, an abdominal aortic aneurysm should also be ruled out.
Imaging
Non-Contrast CT Abdomen and Pelvis
Non-contrast computed tomography (CT) of the abdomen and pelvis is the gold standard for diagnosing acute urinary stones, with sensitivity ranging from 95% to 98% and specificity between 96% and 100%. Low-dose CT protocols, which reduce radiation exposure, maintain comparable sensitivity for detecting stones larger than 3 mm. CT imaging detects all stone compositions, including uric acid and indinavir stones, and identifies secondary signs of obstruction such as hydronephrosis, perinephric stranding, and periureteral edema (the "rim sign"). It also helps exclude alternative diagnoses and allows precise estimation of stone size and location, which is critical for treatment planning. Limitations include radiation exposure, typically around 3-5 millisieverts (mSv) for low-dose protocols, and the inability to detect concurrent urothelial lesions due to the lack of contrast. CT attenuation values measured in Hounsfield units (HU) can help predict stone composition, with uric acid stones generally having attenuation less than 500 HU and calcium stones greater than 500 HU.
Ultrasound
Ultrasound is the preferred initial imaging modality in pregnant patients, pediatric populations, and individuals with a high cumulative radiation burden. It has a sensitivity of approximately 45% for ureteral stones and 70-80% for renal stones. Ultrasound can detect hydronephrosis, which serves as an indirect sign of obstruction. Its advantages include the absence of radiation, bedside availability, and low cost. However, ultrasound is operator-dependent, less effective for detecting ureteral stones, and cannot determine stone composition. The STONE trial published in the New England Journal of Medicine in 2014 demonstrated that an ultrasound-first approach in the emergency department yielded similar clinical outcomes to CT while significantly reducing radiation exposure.
KUB (Plain Radiograph)
Kidney-Ureter-Bladder (KUB) radiographs detect radiopaque stones, primarily calcium-containing stones, but have a sensitivity of only 45-60%. They cannot reliably visualize uric acid, cystine (which appears faintly), or indinavir stones. KUB is useful for follow-up imaging of known radiopaque stones due to its lower cost and radiation compared to CT. Combining KUB with ultrasound improves overall sensitivity in stone detection.
<image>Comparison of CT, ultrasound, and KUB imaging findings in a patient with an obstructing ureteral calculus showing secondary signs of obstruction</image>
Laboratory Assessment
Laboratory evaluation includes urinalysis to detect hematuria, pyuria, bacteriuria, urine pH, and crystal morphology. A urine culture should be obtained if infection is suspected. Basic metabolic panels assess serum creatinine to evaluate for acute kidney injury, as well as potassium and calcium levels. A complete blood count may reveal leukocytosis suggestive of infection. Serum uric acid measurement is useful when a uric acid stone is suspected. In women of reproductive age, a beta-hCG test is essential to rule out pregnancy.
Initial Pain Management
Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ketorolac, diclofenac, and ibuprofen are the first-line treatment for pain in acute renal colic. NSAIDs reduce ureteral smooth muscle spasm and inflammation and have been shown to be as effective as opioids while causing fewer side effects. Typical dosing includes ketorolac 30 mg intravenously or 60 mg intramuscularly, and diclofenac 75 mg intramuscularly or 100 mg per rectum. Opioids like morphine and hydromorphone are reserved as second-line agents for refractory pain. Acetaminophen can be used as an adjunct, with intravenous formulations available. Antiemetics such as ondansetron 4 mg IV are effective for nausea and vomiting. NSAIDs should be avoided in patients with renal insufficiency, a high risk of gastrointestinal bleeding, or those in the third trimester of pregnancy.
Medical Expulsive Therapy (MET)
Tamsulosin, an alpha-1 adrenergic blocker administered at 0.4 mg daily, relaxes ureteral smooth muscle and facilitates stone passage. MET is primarily indicated for distal ureteral stones measuring 5-10 mm. According to the American Urological Association (AUA) and Canadian Urological Association (CUA) guidelines, MET should be offered for distal ureteral stones up to 10 mm when there is no immediate indication for intervention. The efficacy of MET is somewhat controversial; the SUSPEND trial published in The Lancet in 2015 found no benefit over placebo for stones 5-10 mm in size. However, multiple meta-analyses have demonstrated a modest benefit for distal stones larger than 5 mm, with a number needed to treat (NNT) of approximately 4-5. The benefit is greater for larger stones within this range. A trial of MET can last up to 4-6 weeks before considering intervention, and concurrent analgesics and adequate hydration should be prescribed.
Spontaneous passage rates vary by stone size: stones smaller than 5 mm pass spontaneously in 68-98% of cases, those 5-7 mm pass in 40-60%, stones 7-10 mm in 20-30%, and stones larger than 10 mm have less than a 10% chance of spontaneous passage. Stone location also influences passage rates, with distal stones passing more readily than proximal ones.
| Stone Size | Spontaneous Passage Rate | Role of MET |
|---|---|---|
| <5 mm | 68-98% | Marginal benefit; observation preferred |
| 5-7 mm | 40-60% | Beneficial (NNT ~4-5) |
| 7-10 mm | 20-30% | May be offered; intervention often needed |
| >10 mm | <10% | Not recommended; intervention indicated |
<image>Diagram of ureteral anatomy showing the three points of physiologic narrowing (UPJ, pelvic brim/iliac vessels, UVJ) and typical sites of stone impaction</image>
Indications for Urgent Intervention
Urgent intervention is required in several clinical scenarios. An obstructed infected kidney, characterized by sepsis and obstruction, is a urologic emergency necessitating immediate decompression via ureteral stent placement or percutaneous nephrostomy tube insertion. Definitive stone treatment should not be attempted during acute infection. Management includes intravenous antibiotics and hemodynamic support. Other indications for urgent intervention include acute kidney injury due to bilateral obstruction or obstruction of a solitary kidney, intractable pain despite maximal medical therapy, intractable nausea or vomiting preventing oral intake, high-grade obstruction with worsening hydronephrosis on follow-up imaging, and large stones greater than 10 mm with a very low likelihood of spontaneous passage.
Decompression Options
Ureteral Stent (Retrograde)
A ureteral stent is placed cystoscopically under fluoroscopic guidance to bypass the obstruction and allow urine drainage. This approach requires a single anesthetic and is a familiar technique for urologists. However, stent placement can cause symptoms such as urinary frequency, urgency, flank pain, and hematuria. Additionally, a second procedure is necessary for stent removal. Stents should not remain in place indefinitely due to risks of encrustation and infection, with typical duration limited to 4-6 weeks.
Percutaneous Nephrostomy Tube (Antegrade)
Percutaneous nephrostomy tubes are inserted under ultrasound or fluoroscopic guidance by interventional radiology or urology. This method is preferred when retrograde access is not feasible, such as in cases of urinary diversion or ureteral stricture, or in very ill or septic patients since it can be performed quickly under local anesthesia. It is also favored in bilateral obstruction. Disadvantages include the presence of an external tube, risk of dislodgement, and the need for ongoing tube management.
Stent vs. Nephrostomy
Both ureteral stents and percutaneous nephrostomy tubes are equally effective for drainage in cases of obstructed infected kidneys. The choice between them depends on patient-specific factors and institutional expertise. Stents avoid the inconvenience of an external appliance, whereas nephrostomy tubes may be placed more rapidly in critically ill patients.
<image>Fluoroscopic images comparing ureteral stent placement and percutaneous nephrostomy tube placement for an obstructing ureteral stone</image>
Conservative Management and Follow-Up
Conservative management is appropriate for stones 10 mm or smaller without complications. Patients should strain all urine to capture stones for analysis, which is the most cost-effective diagnostic test in stone disease. Follow-up imaging is recommended at 2-4 weeks, using KUB for radiopaque stones, ultrasound, or low-dose CT. Re-evaluation is necessary if the stone has not progressed after 4-6 weeks, if hydronephrosis worsens, if pain increases, or if new infection develops. Referral for definitive treatment, such as ureteroscopy (URS), shock wave lithotripsy (SWL), or percutaneous nephrolithotomy (PCNL), is indicated if the stone fails to pass.
Clinical Pearls
When a patient presents with fever, flank pain, and an obstructing stone, emergent decompression is mandatory, and definitive stone treatment should not be delayed. NSAIDs are the first-line analgesics for renal colic due to their superior side-effect profile compared to opioids and equivalent efficacy. A negative urinalysis for hematuria does not exclude nephrolithiasis. In the emergency department, an ultrasound-first approach is advisable, especially in young patients and women, to minimize radiation exposure; CT should be reserved for cases where the diagnosis remains uncertain. Medical expulsive therapy with tamsulosin is most beneficial for distal ureteral stones measuring 5-10 mm, while stones smaller than 5 mm have a high spontaneous passage rate, making MET benefit marginal. Finally, capturing and analyzing the passed stone is crucial, as it remains the single most cost-effective diagnostic test in stone disease.
References
- AUA/Endourology Society Guideline on Surgical Management of Stones, 2016 (amended 2022)
- Smith-Bindman R, et al. "Ultrasonography versus CT for suspected nephrolithiasis" (STONE Trial). NEJM. 2014;371(12):1100-1110.
- Pickard R, et al. "Medical expulsive therapy in adults with ureteric colic" (SUSPEND Trial). Lancet. 2015;386(9991):341-349.
- Hollingsworth JM, et al. "Alpha-blockers for treatment of ureteric stones." BMJ. 2016;355:i6112.
- EAU Guidelines on Urolithiasis, 2024 Update
- Campbell-Walsh-Wein Urology, 12th Edition, Chapter on Urinary Lithiasis
