Metanephrine mirage: distinguishing the phaeocopies, a case report and literature review

We present one of only seven reported cases of a catecholamine-secreting adrenal neuroblastoma in an adult. The case is used as a platform to discuss key biochemical, genomic and imaging considerations that are central to the successful, targeted management of catecholamine-secreting adrenal tumours.

A 63-year-old male was urgently reviewed at a tertiary hospital endocrinology outpatient clinic for a 12 cm right-sided adrenal incidentaloma. Plasma normetanephrine and 3-methoxytyramine levels were approximately 10 times the upper limit of normal at 9272 pmol/L (< 900) and 1023 pmol/L (< 110), respectively. The adrenal mass appeared to be inseparable from the liver on imaging, and thus was suspected to be an invasive malignant phaeochromocytoma. FDG positron emission tomography (PET)/CT demonstrated moderate to intense metabolic activity within the right adrenal mass. [68 Ga]Ga-DOTATATE (Ga-TATE) PET-CT demonstrated patchy, heterogenous somatostatin receptor (SSTR) expression in the adrenal lesion, at most Krenning 3 (intensity above liver). The patient underwent a right adrenalectomy and segment 6/7 liver resection. Histopathology revealed a 130 mm diameter neuroblastoma of the differentiating subtype with a low Mitosis-Karyorrhexis Index. There was lymphovascular invasion and tumour focally present at the resection margin, but no tumour in one periadrenal lymph node, and no tumour invasion in the adherent liver. Immunohistochemistry revealed ALK positivity (+ 3) and wild type ATRX. At nine months following adrenalectomy, the plasma normetanephrine level has reduced to 991 pmol/L (< 900). Post-operative GaTate PET/CT shows no definite abnormal SSTR-expressing lesions in the surgical bed or elsewhere. The patient has completed adjuvant radiotherapy and is a candidate for ALK-targeted therapy if required for recurrence in the future.

Neuroblastomas may be misdiagnosed as phaeochromocytomas given the ability to secrete catecholamines and similarities in radiological appearance. Differentiating neuroblastomas from phaeochromocytomas and paragangliomas (PPGL) is critical, but clinically difficult. Genomics are central for management; diagnosing ALK-positive neuroblastoma triggers consideration of ALK-targeted therapy, which is not relevant for PPGL. A critical eye is required for the accurate diagnosis and management of malignant adrenal incidentalomas.