PMC6425529_01
Clinical and macroscopic features. (a) Mass of the hard palate. (b) Macroscopic view of the multilobulated lesion (white arrowheads) removed from the hard palate. The tumor measured 2.0 x 1.0 x 0.7 cm.
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The mass was located adjacent to the left maxillary canine and the first and second premolars (Figure 1(a)). Gross examination showed a multinodular and un-encapsulated tumor (Figure 1(b)).
Histological analysis. (a) Unencapsulated tumor composed of multiple round and oval nodules (black asterisk) within the connective tissue. (Hematoxylin and eosin (H&E), magnification x10). (b) The nodules were surrounded by a thin fibrous capsule (black arrow). The tumor was predominantly composed of areas with compact spindle cells (Antoni A tissue). Antoni B tissues (paucicellular area) are infrequent (H&E, magnification x66). (c) In Antoni A tissues, Verocay bodies were found (black asterisk), formed by alternating rows of palisading nuclei (black arrowheads) and intervening nuclei-free stroma. Spindle neoplastic cells had wavy and tapered nuclei, elongated eosinophilic cytoplasm and no discernible cell membrane (H&E, magnification x200). (d) Near Antoni B tissues, blood vessel walls (black arrowheads) were thickened and hyalinized (H&E, magnification x200) (Product Version Olympus VS ASW 2.9).
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In areas with Antoni B pattern, hyalinization of the walls of blood vessels was noticed (Figure 2(a)-(d)).
Immunochemistry analysis. (a) Neoplastic cells (both nucleus and cytoplasm) were strongly immunoreactive for S-100 protein (PS100, magnification x200). (b) Neoplastic cells showed positive nuclear SOX-10 reactivity (SOX-10, magnification x200). (c) The cytoplasm of neoplastic cells was strongly reactive with CD34, only in areas with Antoni B pattern (CD34, magnification x200). (d) Neurofilament protein immunoreactivity (NFP) revealed the occurrence of residual axons within tumor nodules (NFP, magnification x200). (e) Scattered c-kit positive cells were observed in the periphery of nodules and near blood vessels (c-kit, magnification x200). (f) Ki67 /MIB-1 labeling index was heterogeneous and weak (<5%) showing a low risk of malignant transformation (Ki67/MIB-1, magnification x100). (g) INI1/SMARCB1 nuclear immunostaining positivity was diffuse (the expression was retained in more than 90% of neoplastic cells) suggesting a solitary peripheral schwannoma (INI1/SMARCB1, magnification x100) (Product Version Olympus VS ASW 2.9).
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Neoplastic cells exhibited diffuse and strong staining for S100 and SOX-10 (Figure 3(a) and (b)). Focal staining for CD34, neurofilament (NFP) and CD117 (c-kit) was also noted (Figure 3(c)-(e)). Mitotic activity was low (less than four mitoses per 10 high-power fields) and tumor cells had a low Ki-67/MIB-1 labeling index (Figure 3(f)). Moreover, these tumor cells strongly expressed INI1/SMARCB1 (Figure 3(g)).