PMC5990880_01
The findings of neck CT and 18F-FDG PET/CT at surgery, FNA cytomorphologic, and gross examinations of the MC specimens. (a) Neck CT (left) shows an enhanced and relatively well-demarcated nodule with a central low-density area, measuring approximately 22 mm x 18 mm in diameter, arising from the right parotid gland (arrowhead). An axial maximum intensity projection image on coregistered 18F-FDG PET/CT (right) shows an overtly hypermetabolic area in the right parotid gland, corresponding to the neck CT finding. (b) The FNA cytology specimen (Papanicolaou staining) contains a substantial number of small groups or single cells of a mixture of plasmacytoid (inset), oval to spindled, or large epithelioid cells having hyperchromatic pleomorphic nuclei, abundant cytoplasm with occasional inclusion body-like materials, and prominent nucleoli, in a relatively clear background. Original magnification: x400. (c) Furthermore, the FNA cytology (Papanicolaou staining) shows a substantial number of sheet-like clusters of atypical myoepithelial-like cells. Original magnification: x400. (d) A gross examination from the surgical specimen shows a non-capsulated and ill-defined tumor lesion with a grayish to yellowish cut surface, measuring 18 mm x 16 mm in diameter, partly associated with surrounding fat invasion (arrows). Bar = 1 cm.
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Neck computed tomography (CT) showed an enhanced and relatively well-demarcated nodule with a central low-density area, measuring approximately 22 mm x 18 mm in diameter, arising from the right parotid gland (Figure 1(a)). In addition, an axial maximum intensity projection (Figure 1(b)) image on a coregistered 18F-FDG positron emission tomography (PET)/CT revealed an overtly hypermetabolic area in the right parotid gland, corresponding to the above neck CT finding. The specimen from the FNA cytology sample (Figure 1(b) and (c)) contained a substantial number of small groups, single cells (Figure 1(b)), or sheet-like clusters (Figure 1(c)) of a mixture of plasmacytoid, oval to spindled, or large epithelioid cells having hyperchromatic pleomorphic nuclei, abundant cytoplasm with occasional inclusion body-like materials, and prominent nucleoli, in a relatively clear background, on Papanicolaou stain (Figure 1(b)). Radical parotidectomy was thus performed, and a gross examination revealed a non-capsulated and ill-defined tumor lesion with a grayish to yellowish cut surface, measuring 18 mm x 16 mm in diameter, partly associated with surrounding fat invasion (Figure 1(d)).
Microscopic and ultrastructural examinations of the parotid gland MC. (a) Microscopically, this tumor is predominantly composed of the solid proliferation of atypical cells, involving the surrounding fat. Original magnification: x40. (b) Those proliferating tumor nests contain a mixture of oval to spindled, plasmacytoid, or epithelioid cells, often arranged in a trabecular and reticular growth pattern with a patchy eosinophilic hyalinized stroma. On a high-power view, the neoplastic cells have medium-sized, hyperchromatic and enlarged nuclei, often conspicuous nucleoli, and abundant clear to eosinophilic cytoplasm (inset). Original magnification: x200 (inset, x400). (c) Immunohistochemical findings show that those carcinoma cells are specifically and diffusely positive for p63 (left) and cytokeratins, including AE1/AE3 (right). Original magnification: x100. (d) Electron microscopy shows that the phenotype of the carcinoma cells exhibits myoepithelial differentiation, containing many bundles of variably thin actin filaments. Bar = 1 microm. N: nucleus.
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Microscopically, the tumor was predominantly composed of a solid proliferation of atypical cells (Figure 2(a)) including a mixture of oval to spindled, plasmacytoid, or epithelioid cells, often arranged in a trabecular and reticular growth pattern with a patchy eosinophilic hyalinized stroma (Figure 2(b)). On a high-power view, these neoplastic cells had medium-sized, hyperchromatic and enlarged nuclei, often conspicuous nucleoli, and abundant clear to eosinophilic cytoplasm (Figure 2(b)). Furthermore, these tumor nests partly invaded the surrounding fat but there was no perineural infiltration (Figure 2(a)). Immunohistochemical findings showed that the carcinoma cells were specifically and diffusely positive for p63 (Figure 2(c)), cytokeratins, including AE1/AE3 (Figure 2(c)) and CK5/6, and vimentin, whereas they were negative for epithelial membranous antigen (EMA), low-weight cytokeratin (Cam5.2), S-100 protein, alpha-smooth muscle actin (alpha-SMA), bcl-2, and CEA. Electron microscopy showed that this phenotype was consistent with myoepithelial differentiation, as many bundles of variably thin actin filaments were observed (Figure 2(d)).
PMC5990880_02