MAG(3)-F-0 scintigraphy in decision making for emergency intervention in renal colic after helical CT positive for a urolith

Patients with renal colic are evaluated with clinical, laboratory, and imag ing methods for stratification for emergency decompression, medical treatme nt, or discharge and follow up. The current standard practice is heavily ba sed on unenhanced helical CT for detecting uroliths. However. the presence of a urolith does not necessarily mean that the kidney is obstructed and re quires emergency decompression. In this study, technetium-mercaptoacetyltri glycine (MAG(3)) diuretic scintirenography was used to detect obstruction i n patients with renal colic. The contribution of this test to patient manag ement after positive findings from helical CT was also studied. Methods: Di agnostic criteria were established on the basis of previous experience with 60 patients who had renal colic and had undergone radiography of the kidne ys, ureters, and urinary bladder (KUB) acid diuretic Tc-MAG(3) scintirenogr aphy and were followed up to correlate scintigraphic findings with clinical outcome. Subsequently, 80 patients with renal colic underwent scintigraphy within 12 h of presentation in the emergency room, after abdominal helical CT showed findings positive for calculus and suggestive of obstruction. Af ter therapeutic oral or intravenous hydration and analgesics, diuretic dyna mic renal scintigraphy (flow, function, delayed imaging) was performed afte r intravenous injections of 10 mCi (370 MBq) Tc-99m-MAG(3) and 40 mg furose mide (at zero time, or F-0). Results were available soon after completion o f the study and were considered in patient management. Four characteristic patterns of scintirenography, essential in patient stratification and treat ment, had been standardized and were used for interpretation of the studies : the unobstructed kidney; the partially obstructed kidney, proximally or d istally obstructed, with mild to severe obstruction and impairment of funct ion; the totally obstructed kidney, with arrested renal function; and the u nobstructed but dysfunctioning kidney after decompression, or stunned kidne y. Results: Among the 80 patients with positive helical CT findings, 56.5% were found to have obstruction by scintigraphy (32.5% partially, 24% comple tely); the remaining 43.5% did not have obstruction (21% without an indicat ion of recent obstruction and 22.5% with stunned kidneys after spontaneous decompression). Occasionally, findings of preexistent urine extravasation o r infection were present. Patients who, by scintigraphy, never had obstruct ion or had experienced spontaneous decompression did not require admission or emergency intervention; those with complete or severe obstruction requir ed admission and decompression for relief of pain or restoration of functio n, whereas those with mild obstruction were treated variably with forced fl uids, analgesics, or, less frequently, elective surgery. Outcome informatio n from clinical examination, imaging, and interventional findings indicated that this stratification was successful. The test caused no side effects. Conclusion: For renal colic, clinical selection, KUB radiography, and even positive helical CT findings were all found to have a low positive predicti ve value for obstruction (in this study, 35%, 32%, and 56% respectively). A natomic studies, including helical CT, should be followed by diuretic MAG(3 )-F-0 scintirenography to diagnose and quantify or exclude obstruction, det ect spontaneous decompression, and appropriately stratify patients for emer gency intervention, observation and medical therapy, or furtherwork-up and discharge with referral to the clinic.