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Interventional cytopathologist can successfully combine ultrasonographical and microscopic skills to narrow the differential diagnosis in fine needle aspiration of neck paraganglioma

A 51yearold man, upon noticing swelling in his neck, was referred for an ultrasound (US) in a community hospital; the scan hypothesised a parotid origin. Thus, fine needle aspiration (FNA) was performed at our academic institution by an interventional cytopathologist under US guidance. However, the US scan performed by the interventional cytopathologist failed to demonstrate an origin from the parotid gland (Figure 1A). Rapid onsite evaluation (ROSE) of the DiffQuik (DQ) stained smears revealed cells arranged in trabecular and solid groups (Figure 1B); in addition, a pseudofollicular pattern was evident (Figure 1B). Additionally, DQ staining highlighted reddish metachromatic granules within the cytoplasm (Figure 1C); intranuclear cytoplasmic inclusions were also observed (Figure 1D). Based on these features, a preliminary differential diagnosis between a paraganglioma and a metastatic thyroid malignancy, either papillary or medullary thyroid carcinoma, was hypothesised. In view of the potential thyroid malignancy, additional ultrasound imaging of the thyroid gland was performed by the interventional cytopathologist. This revealed a normal thyroid gland, excluding a thyroid origin. An additional FNA pass was performed in order to obtain a cell block (CB) preparation. Haematoxylin and eosinstained CB sections showed solid and trabecular cell groups (Figure 2A) with an evident plasmacytoid cytomorphology (Figure 2B), featuring a diffuse positivity for both chromogranin A and synaptophysin immunomarkers (Figure 2C). Moreover, the S100 immunostain revealed scattered spindle cells at the periphery of the cell groups (Figure 2D). Thus, a final diagnosis of paraganglioma was rendered. Upon this FNA diagnosis, magnetic resonance imaging scans were ordered, revealing a heterogeneous mass closely associated with the jugularcarotid vascular bundle and demonstrating discrete contrast enhancement; any connection with the parotid gland was further excluded. The subsequent surgical specimen showed a firm, rubbery, and well encapsulated 6 cm whitish mass featuring haemorrhagic areas (Figure 3A). The histology slides revealed an organoidpatterned neoplasm composed of polygonal cells featuring abundant eosinophilic and granular cytoplasm; the cells were arranged in nests or lobules partially surrounded by either elongated cells or fibrovascular septa (Figure 3B). The main cells were diffusely positive for chromogranin A and synaptophysin (Figure 3C), whereas the