Symptomatic pheochromocytoma with normal urinary catecholamine metabolites

Area of Science:

• Endocrinology
• Nuclear Medicine
• Oncology

Background:

• Pheochromocytoma, a rare neuroendocrine tumor, typically presents with hypertension and elevated catecholamines.
• Biochemical diagnosis often relies on urinary or plasma metanephrines and catecholamines.
• Diagnostic challenges arise in atypical cases with normal biochemical markers.

Purpose of the Study:

• To report a rare case of symptomatic pheochromocytoma with normal urinary catecholamine and metanephrine levels.
• To emphasize the utility of (131)I-metaiodobenzylguanidine ((131)I-MIBG) scintigraphy in diagnosing pheochromocytoma when biochemical tests are inconclusive.
• To discuss diagnostic strategies for pheochromocytoma in the absence of elevated urinary catecholamines.

Main Methods:

• Clinical presentation of a 61-year-old female with paroxysmal hypertension and an adrenal mass.
• Initial biochemical evaluation including 24-hour urinary fractionated metanephrines, total catecholamines, and vanillylmandelic acid (VMA).
• (131)I-MIBG scintigraphy for functional imaging, followed by surgical resection and histopathological confirmation.
• Post-operative follow-up with (131)I-MIBG scintigraphy.

Main Results:

• CT scan revealed a 4.5cm left adrenal mass.
• All baseline urinary catecholamine and metanephrine tests were within normal limits.
• (131)I-MIBG scintigraphy showed selective radiotracer uptake in the adrenal mass, confirming pheochromocytoma.
• Histopathology confirmed a cystic pheochromocytoma with a solid component.
• Post-operative (131)I-MIBG showed no evidence of residual or recurrent disease.

Conclusions:

• Symptomatic pheochromocytoma can occur despite normal urinary catecholamine and metanephrine levels.
• (131)I-MIBG scintigraphy is a valuable tool for diagnosing pheochromocytoma when biochemical tests are negative but clinical suspicion is high.
• Functional imaging like (131)I-MIBG scintigraphy can aid in confirming the diagnosis and monitoring for recurrence in challenging cases.