SUN-059 - Missed by DOTATATE: How MIBG Uncovered an Adrenergic Pheochromocytoma.

Background:
Functional imaging plays a critical role in the localization of pheochromocytomas and paragangliomas (PPGLs). 68Ga-DOTATATE PET/CT, which targets somatostatin receptor subtype 2 (SSTR2), is commonly favored due to its high sensitivity. However, adrenergic Cluster 2 pheochromocytomas are often epinephrine-predominant, with low SSTR2 expression, which can limit DOTATATE uptake. In contrast 123I-metaiodobenzylguanidine (MIBG, remains highly effective for detecting adrenergic tumors. Recognition of these biological differences is essential to guide appropriate imaging selection and avoid false-negative localization.

Case:
A 70-year-old man with hypertension and atrial fibrillation was referred for an incidental right adrenal nodule. The lesion was new and demonstrated a washout of 44%, concerning for a lipid-poor adenoma versus adrenal neoplasm.

Biochemical Evaluation:
The patient’s labs showed epinephrine-predominant secretion: initial epinephrine 159 pg/mL (0–55.4), norepinephrine 591 pg/mL (115–524), dopamine 28 pg/mL (0–30), metanephrine 141.3 pg/mL (0–88), normetanephrine 322.2 pg/mL (0–285). Supine testing showed epinephrine 115.8 pg/mL, norepinephrine 330 pg/mL, dopamine 25 pg/mL, metanephrine 131.2 pg/mL, and normetanephrine 282 pg/mL.

Imaging and Management:
A 68Ga-DOTATATE PET/CT showed no uptake, highlighting limitations in Cluster 2 tumors. An 123I-MIBG scan revealed avid uptake in the right adrenal lesion, confirming functional disease. The patient underwent right adrenalectomy. Surgical pathology confirmed pheochromocytoma, and post-operative labs demonstrated normal catecholamines and metanephrines confirming biochemical cure. Immunohistochemistry showed a Ki67 index of 6 % with negative SSTR2A, positive Chromogranin A and markedly attenuated S100 staining. A 500 gene molecular panel was sent for further analysis and we await those results.

Conclusion:
This case highlights the importance of recognizing adrenergic Cluster 2 pheochromocytomas. Biochemical phenotype–guided imaging ensures accurate detection of adrenergic Cluster 2 pheochromocytomas, preventing missed diagnoses and guiding timely intervention.

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