A 47-year-old woman complains ofepisodic headaches that began severalmonths earlier and are accompaniedby sweating, flushing, abdominal pain,and vomiting; these attacks have progressivelyworsened. She takes no medicationsand denies fever, chills, andnight sweats. The medical history isunrevealing.
A 47-year-old woman complains ofepisodic headaches that began severalmonths earlier and are accompaniedby sweating, flushing, abdominal pain,and vomiting; these attacks have progressivelyworsened. She takes no medicationsand denies fever, chills, andnight sweats. The medical history isunrevealing.This thin patient is in no acutedistress. Temperature is 37.2oC(99oF); heart rate, 78 beats per minute;respiration rate, 23 breaths perminute; and blood pressure, 164/93mm Hg. Results of a physical examinationare normal. Electrolyte levelsand sodium and potassium levels arealso normal. You order an MRI scanto rule out renal artery stenosis. Resultsof the scan are negative; however,on one of the sequences, the radiologistnotes "a suggestion of an adrenal lesion."Urinalysis results are positivefor vanillylmandelic acid.Which diagnostic test is most appropriatein this setting--and why?WHICH TEST--AND WHY:In this setting,a nuclear medicine I 131 metaiodobenzylguanidine(MIBG) study isthe optimal method of confirming asuspected pheochromocytoma. First,it is a whole-body scan. Although approximately85% of pheochromocytomasoccur within the adrenal medulla,the remaining 15% can occur anywherefrom the neck to the sacrum,with the majority of these extra-adrenallesions found below the diaphragm.Multiple lesions occur in10% of patients; adults with familialsyndromes and children are morelikely to have multiple lesions.The sensitivity of an I 131 MIBGscan is about 90%; thus, it will locatethe vast majority of pheochromocytomas. Moreover, the specificity ofthe scan is over 95%, which makes afirm diagnosis possible.Results of the MIBG scan. Seventy-two hours after intravenous administrationof the radiopharmaceutical,this patient's posterior imagesreveal a focal area of increased activityin the left upper quadrant of theabdomen; this area has increased inintensity on the delayed, 96-hourimages (Figure 1).A contrast-enhanced CT scan isobtained for preoperative anatomicimaging. Before the scan, the patientreceives an αblocker regimen to preventa hypertensive crisis. Axial imagesshow a 3-cm lobulated lesion inthe left adrenal gland that is consistentwith a pheochromocytoma(Figure 2).Outcome of this case. The leftadrenal gland was surgically removed,and the patient's symptoms resolvedcompletely.