Oral plexiform schwannoma: A case report and relevant immunohistochemical investigation

Abstract

Schwannomas are benign peripheral nerve sheath tumors originating from the Schwann cells. Most schwannomas in the head and neck region are solitary; however, multiple schwannomas affecting one or more nerves suggest a possible association with neurofibromatosis type 2 and schwannomatosis. Plexiform schwannoma is a rare variant of conventional schwannoma that is characterized by intraneural multinodular growth. This grow pattern has also been observed with other neural tumors which may make diagnosis more difficult. Herein, we report the case of a 28-year-old woman who presented a solitary plexiform schwannoma of great palatine nerve. In the present case, we focused on immunohistochemical analysis in daily practice for the differential diagnosis of schwannomas and their mainly morphological mimics, especially with plexiform neurofibroma, granular cell tumor and malignant peripheral nerve sheath tumors. We also discussed on SMARBC1/IN1 marker usefulness in combination with brain magnetic resonance imaging for the distinction of solitary schwannoma from neurofibromatosis type 2 or schwannomatosis.

Keywords: INI1/SMARCB1; Plexiform schwannoma; benign peripheral nerve sheath tumors; immunohistochemistry; oral cavity.

Figure 1.

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 × 1.0 × 0.7 cm.

Figure 2.

Histological analysis. (a) Unencapsulated tumor composed of multiple round and oval nodules (black asterisk) within the connective tissue. (Hematoxylin and eosin (H&E), magnification ×10). (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 ×66). (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 ×200). (d) Near Antoni B tissues, blood vessel walls (black arrowheads) were thickened and hyalinized (H&E, magnification ×200) (Product Version Olympus VS ASW 2.9).

Figure 3.

Immunochemistry analysis. (a) Neoplastic cells (both nucleus and cytoplasm) were strongly immunoreactive for S-100 protein (PS100, magnification ×200). (b) Neoplastic cells showed positive nuclear SOX-10 reactivity (SOX-10, magnification ×200). (c) The cytoplasm of neoplastic cells was strongly reactive with CD34, only in areas with Antoni B pattern (CD34, magnification ×200). (d) Neurofilament protein immunoreactivity (NFP) revealed the occurrence of residual axons within tumor nodules (NFP, magnification ×200). (e) Scattered c-kit positive cells were observed in the periphery of nodules and near blood vessels (c-kit, magnification ×200). (f) Ki67 /MIB-1 labeling index was heterogeneous and weak (<5%) showing a low risk of malignant transformation (Ki67/MIB-1, magnification ×100). (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 ×100) (Product Version Olympus VS ASW 2.9).