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Flank pain: rarely AAA, usually a kidney stone; The odds of a ruptured abdominal aortic aneurysm are very small, but real.

WASHINGTON -- Most patients presenting with flank pain turn out to have kidney stones, but there is a very small but real potential that the cause may be a ruptured abdominal aortic aneurysm, according to Flavia Nobay, M.D., who spoke at the annual meeting of the American College of Emergency Physicians.

In general, 10% of men and 3% of women will experience a kidney stone, and 70% of kidney stones occur in people aged 20-50 years. The main risk factor is a previous stone; a family history of kidney stones is also predictive, making it 2.5 times more likely the patient will have a stone.

If patients present with unilateral cost-vertebral angle pain, abrupt onset of pain, and hematuria, there is a 90% probability of having a stone, said Dr. Nobay, of the division of emergency medicine at the University of California, San Francisco.

Yet it is still important to be certain of the diagnosis, she said. For instance, 10%-30% of stones are negative for hematuria, and patients often present writhing in pain, which also occurs with aortic dissection.

For the 10% of patients who do not have stones, there is a variety of potential diagnoses. A 1993 study in the European Journal of Vascular Surgery found that 9.5% of patients older than 65 years who were referred for renal colic imaging were diagnosed with aortic dissection, but that study has never been replicated, Dr. Nobay said.

However, one-quarter to one-half of abdominal aortic aneurysm (AAA) cases are misdiagnosed, and the most common misdiagnosis is a renal stone, she said. The risk factors for AAA include a first-degree relative with dissection, smoking, hypertension, peripheral vascular disease, and undifferentiated flank pain.

The best way to differentiate between AAA and a kidney stone is to take a careful history and use CT scans, although CT imaging can't be done with unstable patients.

Vascular catastrophe is rare, however, affecting only 0.18% of patients with acute flank pain, Dr. Nobay said. Among the other potential diagnoses are herpes zoster, appendicitis, pyelonephritis, diverticulitis, and bowel obstruction. She said she usually gets several laboratory measures: a urinalysis for hematuria, leukocytes, and nitrites and a BUN with creatinine, which gives, at minimum, a baseline of kidney function.

CT imaging studies should be conducted in patients with no prior history of stones and in patients who have an unclear diagnosis, an underlying renal disorder, or are febrile. A CT scan is highly accurate except in patients taking indinavir, which makes kidney stones radiolucent. Current protocols call for 3-5-mm cuts without intravenous contrast.

Though a scan can't give any data on kidney function, it can help diagnose hydronephrosis, hydroureter, and perinephric stranding--all of which are secondary signs of stones, she said.

If no kidney stone is found on a CT scan, the stone could be between the cuts or it may recently have been passed.

Ultrasound is good for spotting proximal stones that are larger than 5 mm, intracalyceal stones, and distal stones at the ureterovesical junction. And unlike CT scans, there's no radiation exposure, and it is less expensive.

But the method might miss some stones, because it provides inadequate imaging of the renal collecting system and the ureter, and it is very much operator dependent, she said. It is a promising technology, but is not superior to CT, Dr. Nobay said.

The intravenous pyelogram provides high sensitivity and specificity for stones, but the procedure is not as cost-effective as CT, she said.

Kidney stone patients should be given pain medication, starting with intravenous ketorolac and other nonsteroidal anti-inflammatory drugs, which are often as effective as opiates, Dr. Nobay said.

Many clinicians have made the mistake of overhydrating patients; but if patients are already adequately hydrated, more fluid will cause a bigger fluid backup, leading to more pain, Dr. Nobay said. Only moderate hydration is necessary.

Stones of less than 2 mm pass in 8 days on average; 2-4 mm stones take about 12 days, and those larger than 4 mm pass in an average of 22 days. Patients with stones larger than 7 mm, or those who have failed on pain medications after 2-4 weeks, need an urgent urological consultation.

In the past, surgeons looked only at stones larger than 5 mm for intervention, but the size recently has been increased to 7 mm. Dr. Nobay said.

BY ALICIA AULT

Contributing Writer
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Title Annotation:Cardiovascular Medicine; abdominal aortic aneurysm
Author:Ault, Alicia
Publication:Internal Medicine News
Geographic Code:1USA
Date:Dec 1, 2005
Words:729
Previous Article:Proteinuria linked to MI deaths.
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