A Compelling Case Report of Intraoral Cellular Schwannoma Involving Buccal Vestibule

INTRODUCTION

Schwannoma is a benign, encapsulated tumor that arises from the Schwann cells that cover the nerve sheath. It is sometimes referred to as neurilemmoma, neurinoma, or perineural fibroblastoma. These tumors, which were initially reported by Verocay in 1908, can arise from any cranial, peripheral, or autonomic nerve that contains Schwann cells.^[1] While 25-45% of schwannomas occur in the head and neck, occurrences in the oral cavity are less than 1%.^[2] The tongue, palate, floor of the mouth, lips, jaws, and buccal mucosa are the most often seen intraoral locations. Schwannomas manifest as smooth submucosal enlargement in the soft tissues of the mouth. Histological differential diagnosis should be made with other neural origin lesions, including neurofibromas and neuromas, as well as tumors of muscular or fibroblastic origin.^[3] High cellularity and a variety of growth patterns, including fascicular, storiform, and herringbone patterns, make it difficult to identify schwannomas. Among the histological variations, cellular schwannoma is a rare histopathological variant. Microscopic characteristics like hypercellularity and pleomorphism can create a misleading appearance of malignancy. Consequently, to confirm that the tumor is benign and avoid unnecessary treatment, a thorough examination is necessary.^[2]

Here, we describe a 40-year-old female patient who had a rare case of intraoral cellular schwannoma affecting the buccal vestibule of the left maxilla. As far as we know, only three cases of intraoral cellular schwannoma^[2,4,5] and two cases of buccal vestibule schwannoma^1,3 have been documented in the literature to date.

CASE REPORT

A 40-year-old female patient reported a chief complaint of a painless swelling in the upper left jaw region for the past 1year. The past medical and family history were not relevant. Extra oral examination revealed facial asymmetry extending from the ala of the nose to the region corresponding to the middle of the eyes. Intra-oral examination revealed a movable and well-circumscribed swelling in the maxillary left buccal vestibule in relation to 24,25, and 26 [Figure 1].

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Figure 1:

A 40-year-old female patient presented with painless swelling in the left maxillary region. Intraoral photograph depicts a well-circumscribed swelling (circled) in the maxillary left buccal vestibule in relation to 24, 25, and 26.

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On palpation, the swelling was firm in consistency, non-tender, with no bleeding. Based on the clinical examination, the provisional diagnosis was lipoma. The swelling was surgically excised under local anesthesia and subjected to histopathological examination. Macroscopically, the excised tissue was white in color and soft in consistency, measuring 3×2 cm. On the day of receiving the specimen, it was seen floating on the fixative solution [Figure 2].

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Figure 2:

Excised and grossed specimen.

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On histopathological examination, Hematoxylin and Eosin (H & E) - stained sections revealed a well-circumscribed tumor mass surrounded by a fibrous capsule with a highly cellular connective tissue stroma composed of Schwann cells arranged in variable patterns, predominantly as short interlacing fascicles. The majority of the areas were highly cellular, consisting of spindle-shaped cells with blunted nuclei that were serpentine, wavy, or cigar-shaped, and indistinct cytoplasmic borders. There was also sporadic whirling, a few palisading areas, and hyperchromatic nuclei, which were suggestive of Antoni A areas without Verocay bodies. Occasionally, hypocellular areas containing loosely arranged cells along with microcystic spaces and focal areas of degeneration resembling Antoni B areas were also seen [Figure 3].

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Figure 3:

Short interlacing fascicles showing highly cellular Antoni A (red arrow) and Antoni B with lack of verocay bodies (yellow arrow).

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Results from immunohistochemistry revealed that tumor cells had broad, high nuclear and cytoplasmic positivity with S100 protein, which confirms the neural origin of the lesion^[5] [Figure 4a]. Focal moderate nuclear positivity among tumor cells with SOX 10, a nuclear transcription factor for Schwannian cell differentiation^[6] [Figure 4b]. Diffuse strong positivity among tumor cells with CD 34 [Figure 4c], diffuse strong nuclear and cytoplasmic positivity with vimentin [Figure 4d]. Focal positivity around blood vessels with the α-smooth muscle actin (SMA), thereby leading to a diagnosis of Schwannoma. The cellular variant of Schwannoma was confirmed based on the histological and immunohistochemical analysis.

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Figure 4:

(a) Immunohistochemistry shows diffuse strong nuclear and cytoplasmic positivity in tumor cells with S100 protein (40x), (b) Focal moderate nuclear positivity among tumor cells with SOX 10 (40x), (c) Diffuse strong positivity among tumor cells with CD34 (40x), (d) Diffuse strong nuclear and cytoplasmic positivity with Vimentin (40x).

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DISCUSSION

The term 'Schwannoma' was historically used to refer to either neurofibroma or neurilemmoma. However, it is now understood that neurofibromas originate from perineural cells, while schwannomas arise from Schwann cells. Thus, Neurilemmoma and Schwannoma are interchangeable terms.^[2] Oral schwannoma is an uncommon, solitary, and slow-growing neural tumor that generally does not cause symptoms. Although it can develop at any age, it is most frequently observed in people aged 30 to 50.In the case presented, it occurred in the fourth decade. In this instance, the female-to-male ratio of 1.6:1 indicates a noticeable female predilection. ^[3,5]

In 25% to 45% of cases, the head and neck area is home to extracranial schwannomas. However, they only make up 1% of all head and neck tumors, making their incidence in the mouth extremely uncommon.^[3] In the oral cavity, the tongue is the most frequently affected, followed by the roof of the mouth, the floor of the mouth, the buccal mucosa, the gingiva, the lips, and the vestibular mucosa.^[1] Other benign lesions, including mucocele, fibroma, lipoma, and benign salivary gland tumors, might have similar clinical presentations. The tumor may be intraosseous in certain cases, more commonly in the mandible, where it may cause bone growth, discomfort, and paresthesia. Cysts and odontogenic tumors are common diagnoses in these cases.^[3] In this particular case, the Schwannoma was located extraosseously in the buccal vestibule, a site that is rarely affected. Following the clinical examination, the provisional diagnosis was lipoma. Initially, no particular hypothesis was generated regarding Schwannoma due to its rarity as an oral lesion, especially within the buccal vestibule.

Schwannoma presents numerous histopathological variants. Traditionally, it is divided into two histological patterns: Antoni-A (marked by hypercellularity) and Antoni-B (marked by hypocellularity). Furthermore, additional histopathological variants include ancient, pseudoglandular, plexiform, cellular, epithelioid, and melanotic schwannoma.^[3] Khadse et al. describe that Schwann cells were arranged in palisading patterns, forming Antoni A areas.^[6] Acellular eosinophilic verocay bodies were observed between the palisading cells, and Antoni B areas exhibited loosely arranged spindle cells in a myxoid stroma.^[6] The 14 cases of cellular schwannoma reported by Woodruff et al. (1981)^[7] showed histological features such as nuclear pleomorphism, hyperchromatism, heightened cellularity, lack of Verocay bodies, and frequently enhanced mitotic activity. All of these traits were evident in the current case.

Immunohistochemically, S100 is crucial for distinguishing neoplasms originating from neural crest cells from those of non-neural origin. Cellular schwannoma typically demonstrates strong diffuse expression of S100, as observed in the case presented. Finally, Cellular Schwannoma can imitate malignant peripheral nerve sheath tumors (MPNST) when it exhibits more aggressive characteristics. S100 immunohistochemistry is crucial in this case because MPNST hardly ever expresses robust diffuse S100, although cellular Schwannoma frequently does.^[8] Sox10 is a useful diagnostic marker for many malignancies of the peripheral nerve sheath, including granular cell tumors, MPNST, neurofibroma, and Schwannoma. In this particular case, Sox10 exhibited focal moderate nuclear positivity among the tumor cells. The Antoni A areas of schwannomas and fibroblasts of all neurofibroma subtypes exhibit widespread expression of the transmembrane phosphoglycoprotein CD34^[9], similar to our findings. In this case, the tumor also exhibited strong positivity for Vimentin, similar to the case reported by Bhalerao et al.^[5] and α-smooth muscle actin (SMA) around the blood vessels.

The full surgical removal of the tumor is the recommended course of treatment. Recurrence is rare and usually happens when anatomical constraints prevent the excision from being completed.^[1] The prognosis is highly favorable, and malignant transformation is rare.^[2] In this instance, the lesion was encapsulated, and despite its large size, postsurgical healing proceeded normally.

CONCLUSION

Schwannomas in the buccal vestibule are extremely uncommon, and based on the available literature, no case reports of cellular Schwannoma in this location exist in the current literature. Schwannoma should be taken into consideration as a potential diagnosis when assessing a well-defined soft tissue mucosal lesion in the oral cavity. Due to its rarity, this lesion can be clinically indistinguishable from other benign soft tissue and salivary gland tumors. Cellular Schwannoma, histopathologically, due to its hypercellularity, can lead to misdiagnosis as a malignant tumor. Therefore, a definitive diagnosis necessitates clinical assessment, histopathological examination, and immunohistochemical analysis.