False positive diagnosis of a paraganglioma of the organ of Zuckerkandl

Samir Damji, Rashpal Flora, Jeannie Todd, Fausto Palazzo, Imperial Healthcare NHS Trust.

Case: A 66-year-old lady was discovered to have a 3.7cm mass at the aortic bifurcation after being investigated for back pain. She had a past medical history of endometrial carcinoma, diagnosed 18 years ago and subsequently underwent a total hysterectomy and external beam radiotherapy. Following an MDT review, a suspicion was raised that the lesion may have been a paraganglioma. Subsequent testing for urinary metanephrines was negative however a there was a borderline increase in plasma metanephrine of 1290 pmol/L, with a normal upper limit of 1180 pmol/L. Molecular genetic testing for familial paraganglioma/phaeochromocytoma did not detect a pathogenic variant. The patient underwent whole body 68Gallium DOTATATE PET-CT scanning, which identified avid uptake of tracer and somatostatin receptor positivity in the mass at the aortic bifurcation, in keeping with a paraganglioma of the organ of Zuckerkandl. Following review at the NET MDT a decision was made to proceed with surgical resection and the patient underwent pre-operative anaesthetic assessment and optimisation with alpha-blockade. An open resection of the paraganglioma with lymphadenectomy was performed and the patient made an uncomplicated recovery and was discharged on the 6th post-operative day. The histopathological analysis of the mass at the aortic bifurcation showed a 30mm lymph node infiltrated by a metastatic malignant tumour. The morphology and immunoprofile was in keeping with a metastatic carcinoma of the female genital tract, likely a poorly differentiated endometrial carcinoma. There was no evidence of a paraganglioma.

Discussion: Neuroendocrine tumours arising from extra-adrenal ganglia are rare tumours, however they are associated with high morbidity and mortality. Whilst the mainstay of treatment is surgical resection, the diagnosis and localisation is often challenging and complex. However, with the increasing advancement and availability of PET imaging, somatostatin analogues have been labelled with positron emitting isotopes such as Gallium-68, to image somatostatin receptor expressing neuroendocrine tumours. It has been demonstrated that 68Ga-DOTATATE PET scans can significantly improve the spatial resolution and lesion detectability compared to MIBG scintigraphy, CT or MRI. A number of studies have confirmed a sensitivity between 85%-100% and specificity between 82%-90% in the ability to diagnose NETs. Although a highly sensitive and specific imaging modality, and whilst extremely rare the physician must be aware of physiological and pathological processes which may lead to interpretive errors. We present the first described metastatic, endometrial carcinoma with somatostain receptor expression resulting in a false positive diagnosis of a paraganglioma of the organ of Zuckerkandl.