Clinical, genetic, radiological characteristics and management of mediastinal paragangliomas: a literature review and case series.

Paragangliomas (PGLs) are neuroendocrine tumours (NETs) that arise from neural crest derived cells. Up to 40% of cases occur due to the presence of a pathogenic germline variant (PGV) in a known gene. Mediastinal PGLs are rare but are being diagnosed with increasing frequency. Treatment generally involves surgery but is complicated in mediastinal PGLs due to their anatomy. Here we will perform a literature review and discuss our experience with 18 such cases. Cases were identified via the Guy's and St Thomas' NHS Foundation Trust NET multidisciplinary team database. Tumours ranged in size from 0.6cx0.6cm to 6.8cmx4.9cm. 72.2% were associated with a PGV of SDHB or SDHD. 22.2% developed metastatic disease but it was only possible to attribute 50% of these to a mediastinal primary. (68Ga)-DOTATATE PET CT demonstrated 100% sensitivity. Literature review identified 233 cases. A PGV was reported in 81% of cases with metastatic disease in approximately 39.2%. It was not possible to confirm that all cases of metastatic disease were secondary to a mediastinal primary. Our experience confirms the high rate of mediastinal PGLs arising in the presence of a PGV. The lower rate of metastatic disease in our cohort (11.1%) likely represents earlier diagnosis thanks to the application of screening protocols and the increased sensitivity of (68Ga)-DOTATATE PET CT. With this increased sensitivity we have diagnosed small mediastinal PGLs which were not evident on alternative imaging modalities. In the absence of growth or catecholamine secretion, the need to intervene on these is unclear.