SUN-910 High Enhancement Washout by CT Imaging Does Not Exclude Pheochromocytoma/Paraganglioma: Review of Two Cases

Background: It is well known that delayed images from contrast-enhanced CT are useful in distinguishing adrenal adenomas from non-adenomas, with an absolute washout that exceeds 60% being most consistent with a lipid rich adenoma. We present two cases of an adrenal mass that met the criteria for a lipid rich adenoma by CT imaging, but found to be a pheochromocytoma (PCC) and paraganglioma (PGL). Clinical Case Case#1 An 82 yo woman presenting with tachycardia was found to have a 2.4 cm heterogeneously attenuating, left adrenal nodule with an absolute washout of 61% and a relative washout of 45%. The right adrenal was normal. Urinary catecholamine levels were elevated with an epinephrine (E) 38 mcg (2–24), norepinephrine (NE) 388 mcg (15–100), dopamine (DOPA) 175 mcg (52–480), metanephrine (MN) mcg 620 (90–315), normetanephrine (NMN) 1553 mcg (122–676) and vanillylmandelic acid 12.5 mg (< 6) on a 24h collection. Due to a cardiac resynchronization therapy device, an MRI could not be obtained. MIBG imaging was obtained and showed increased uptake in left adrenal gland, corresponding to the lesion identified on CT. The patient underwent laparoscopic adrenalectomy and the pathology confirmed a PCC. Case#2: A 74 yo man was found to have an incidental right adrenal nodule on CT imaging measuring 2.4 cm. Absolute washout was 83% and relative washout 68%. The left adrenal gland was normal. A follow up MRI obtained showed slight increase in T2 weighted images and no drop out on out of phase imaging, raising concern for a PCC. Urinary catecholamines were elevated including E 12 mcg (2–24), NE 280 mcg (15–100), DOPA 246 mcg (52–480), MN 175 mcg (90–315) and NMN 1298 mcg (122–676) on a 24-hr. collection. MIBG imaging further confirmed the diagnosis with increased uptake in the right adrenal gland. The patient underwent laparoscopic adrenalectomy then, converted to open right adrenalectomy through an anterior approach due to adherence of the tumor to the renal vein. The pathology revealed a PGL. Conclusion: PCC/PGL are rare but life-threatening neuroendocrine tumors that require early detection to reduce associated morbidities and mortality and improve surgical outcomes. CT is commonly used to characterize adrenal lesions and an absolute washout of >60% is most consistent with an adenoma. However, as demonstrated by these two cases, washout exceeding 60% can also be seen in non-adenomas, perhaps secondary to degeneration of the nodule causing necrotic or cystic changes or uncommonly, the presence of a high lipid content in the tumor [1]. Thus, when clinical suspicion is strong and/or there is a positive biochemical workup, confirmatory imaging should be considered to establish the diagnosis. References: [1] Blake, M. A., Kalra, M. K., Maher, M. M., Sahani, D. V., Sweeney, A. T., Mueller, P. R., ... & Boland, G. W. (2004). Pheochromocytoma: an imaging chameleon. Radiographics, 24(suppl_1), S87-S99.