Symptomatic pheochromocytoma with normal urinary catecholamine metabolites

Abstract

A 61-year old female presented with paroxysmal hypertension and a 4.5cm left adrenal mass on CT scan. Repeated measurements of 24-hour urinary fractionated metanephrines, total catecholamines and vanillylmandelic acid (VMA) were within normal range. A further scintigraphic study with 131 I -metaiodobenzylguanidine ( 131 I-MIBG) revealed selective concentration of the radiotracer, corresponding to the CT mass. After adequate preoperative treatment, successful surgical excision of the tumor was performed and the pathological examination confirmed the diagnosis of a cystic pheochromocytoma with a 2cm solid tumor. On reevaluation three months later using 131 I-MIBG, no evidence of remaining or recurrent disease was found. The patient, off any antihypertensive medication, reported mild recurrent hypertension and panic attacks that were adequately controlled with antidepressants. This is a rare case of a symptomatic pheochromocytoma without elevated urine catecholamines and metanephrines. According to the literature, plasma free metanephrines would be the ideal test for biochemical detection of the tumor. However, in the event that they are not available and there is a high clinical suspicion for the presence of pheochromocytoma, as in our patient, we suggest performance of a functional nuclear medicine study, such as 131 I-MIBG, to confirm the clinical diagnosis.

Value of Systemic Hormonal Unloading in Pheochromocytoma

“…Plasma and urinary catecholamines can be normal in episodically secreting tumors when measured between paroxysmal attacks, also in the presence of so-called non-functional or silent tumors. [6] These are the possible reasons why our patients had normal 24-hour urine metanephrine.…”

False Positive Radioiodinated Metaiodobenzylguanidine (123I-MIBG) Uptake in Undifferentiated Adrenal Malignant Tumor

“…In addition, in patients diagnosed with pheochromocytoma through biochemical testing, the combined use of MRI and 123 I-MIBG scintigraphy has a sensitivity and positive predictive value of 100%; even in patients with symptomatic pheochromocytoma and normal urinary catecholamine metabolites, positive uptake in 123 I-MIBG scintigraphy is seen. Taken together, this demonstrated the effectiveness of 123 I-MIBG scintigraphy in diagnosis of pheochromocytoma [ 13 , 14 ].…”

A rare serious case of retroperitoneal paraganglioma misdiagnosed as duodenal gastrointestinal stromal tumor: a case report

“…If assay error is excluded, urinary total metanephrines could be false negative (as in our case), in episodically secreting tumors when measured between paroxysmal attacks. In such a case, it is better to do the test during or soon after symptomatic crisis [5,10]. Biochemically silent PGL in patients with SDHB mutation is a potential other cause for normal plasma or urinary fractionated metanephrines.…”

“…When PLG is still clinically suspected inspite of negative investigations, 123 I-metaiodobenzylguanidine (MIBG) scintigraphy is recommended to detect the tumor (unavailable in our institute) [10,12]. Fine needle aspiration cytology shouldn't be performed because of the fear of stimulating hypertension crisis [3].…”