| Suspect Renal Colic
Imaging Strategies Author: Charles Allison, MB ChB Editor: Ashley Davidoff MD The Common Vein Copyright 2006 CLINICAL BACKGROUND – The classical presentation of renal colic is loin to groin pain with hematuria. Renal colic is a acute pain caused by acute obstruction of the urinary collecting system, by a stone that has become dislodged from the kidney and become lodged in the ureter. Ureterolithiasis is most commonly asponataneous event but is sometimes associated with decreased fluid intake, dehydration and subsequent urinary concentration. It is also associated with increased intake of oxalates. Clinically the pain syndrome that results is classically associated with flank pain, or “loin to groin pain”, though isolated groin pain is possible. The pain is usually excruciating and possibly the most severe pain the patient has experienced. Hematuria is very common. WHAT STUDY? An abdominal CT scan without i/v nor oral contrast is the preferred initial study. There is no reason to get a plain film of the abdomen since oral contrast is not needed and there should be no delay in getting the CTscan within 30 minutes of request. In pregnant patients, or young patients, an US is a reasonable choice to identify kidney stones, hydronephrosis (which may not be present in the early stages of obstruction), and to evaluate ureteral jets in the urinary bladder. WHY? CT scanning is highly sensitive and specific. (>90%). The plain film of the abdomen may show the calcification but cannot accurately localize nor size the stone, and is unable to reveal the presence of hydronephrosis. Cysteine and urate stones are partially opaque and cannot be visible on plain X-ray, but they are easily seen on CT because they contain components which is make them hyperdense. Ultrasound is able to identify nephrolithiasis and hydronephrosis but it is usually unable to diagnose ureterolithiasis unless the stone is at the UVJ. The size and position of the stone in the ureter, as well as the presence of hydronephrosis are important facts that guide the urologist for “next step” strategy. This may be conservative management if the stone is less than 3-4mms and lies in the distal ureter, or it may require intervention if it larger than 5mms, and is in the more proximal portions of the ureter. The non-contrast (no i/v) technique enables both opaque and non opaque stones to be identified. Once there is i/v contrast in the collecting system the stones may be masked. BACKGROUND TO THE DISEASE: Renal stones occur in 2-3% of the population, particularly when the patient is dehydrated. Most are radio-opaque (90%) and can be divided into oxalate stones (60%), triple phosphate stones (30%) and cysteine stones (partially opaque due to sulfur content). Radiolucent stones are typically formed from urate (5-10%). Oxalate stone occur with dehydration, hypercalceamia, and renal tubular acidosis. Triple phosphate (magnesium, calcium and ammonium phosphate) stones are typically “staghorn” calculi that remain in the renal pelvocalyceal system. They occur secondary to Proteus urinary tract infection (alkalinisation of urine). Cysteine stones are associated with homocysteinuria. The commonest places for renal stones to become obstructed are at the pelvo-ureteric junction (PUJ), at the sacroiliac joint as the ureter crosses it, and at the distal end of the ureter as it passes obliquely through the bladder wall to empty into the bladder. Two thirds of stones will pass spontaneously with conservative management and hydration, often with 48 hours. The remainder may need surgical removal (ureteroscopic, percutaneous or via ESWL, Extracorporeal ShockWave Lithotripsy). WHEN? CT scanning should be performed at time of presentation, as the patient requires immediate management. HOW TO ORDER? The symptoms or signs that should be added to the request would include “RLQ pain, no hematuria r/o uretrolithiais” and study requested is CTscan for “kidney stone protocol”. The patient has to lie still on the table for the 50-70second scan, and thus needs adequate control of the pain before coming to radiology. PATIENT PREPARATION No preparation for the study is necessary and the patient should be accomodated in the next open spot on the scanner. The study takes about 1 minute once the patient is on the table CLINICAL RED FLAGS: Fever or signs of sepsis may indicate pyonephrosis – infection in an obstructed system proximal to the stone. This requires immediate antibiotics and possible nephrostomy to decompress the system.
REFERENCES: Web References American College of Radiology Acute Onset Flank Pain, Suspicion of Stone Disease Family Practice Notebook Oxford Handbook of Acute Medicine – P. Ramrahka, K. Moore; Oxford University Press 2001) |