Endocrine Abstracts

Case: We report a rare case of a primary cardiac paraganglioma. A 49-year-old male was found to have elevated3-methoxytyramine (3-MT) levels with normal metanephrines, having undergone a screening test following discovery of SDHB gene mutation, after his 10-year-old niece developed a phaeochromocytoma.

The patient demonstrated no hypertension and did not bear signs of catecholamine excess, but on direct questioning had experienced palpitations. Biochemistry revealed persistently high serum and urine 3-MT (3xULN), and normal adrenaline and nor-metadrenaline metabolites. MRI head and neck and ¹²³I- MIBG scans were normal, whilst CT chest showed indeterminate lung nodules. ¹⁸F- FDG-PET scan showed an area of high uptake suggestive of a paraganglioma in the thorax.

Cardiac MRI showed a 3.7x2.9 cm lesion in the inter-atrial groove extending superiorly between the junction of the right upper pulmonary vein and left atrium, compressing the superior vena cava. The patient was alpha- and beta blocked in preparation for thoracic surgery.

Progress: Before the planned surgical intervention the patient presented as an emergency with chest pain, requiring urgent cardiac bypass surgery for resection of the cardiac tumour and atrial walls, given intraoperative exploration revealed tumour invasion into interatrial septum.

Discussion: Paragangliomas in the chest are uncommon, accounting for less than 2% of systemic paragangliomas. Primary cardiac paragangliomas are an extremely rare finding. The association between SDH mutations and primary cardiac paraganglioma is reported in the literature, however the anatomical location of interatrial groove in this case is unusual. In this case, the elevated 3-MT level in both plasma and urine was a key finding leading to the diagnosis.

Learning points: • Interatrial groove is a rare anatomical location for a catecholamine excess tumour

• False negative ¹²³I- MIBG is common in extra-adrenal phaeochromocytoma/paraganglioma associated with SDHB mutations

• Persistent isolated elevation of 3-MT in patients with known high-risk genetic inheritance should prompt comprehensive evaluation.