Lower Lip Plexiform Schwannoma: Report of a Rare Case and a Literature Review.

Plexiform schwannoma is an uncommon benign neoplasm of the neural sheath characterized grossly and microscopically by multinodular growth. It is typically presented as a mobile, solitary, smooth-surfaced, and nontender mass. Histologically, schwannomas are classified into the following seven types: classical (Verocay), plexiform, cellular, cranial nerve, melanotic, degenerated (ancient), and granular cell schwannomas. In spite of the fact that plexiform schwannoma commonly occurs in the head-and-neck region, the involvement of the lip is considered to be extremely rare. Herein, we present the case of a 16-year-old boy with the schwannoma on the lower lip excised without any recurrence at 9 months after surgery.

Introduction

Schwannoma (neurilemmoma) is a neurogenic benign neoplasm that originates from the Schwann cells of the nerve sheath.[12] This neoplasm arises at any age without any gender predilection.[2] Plexiform schwannoma is an infrequent benign neoplasm of the neural sheath characterized grossly and microscopically by multinodular growth.[3] Approximately 5% of schwannomas have a plexiform or multinodular growth pattern. This rare benign tumor is worthy of recognition because it can be misdiagnosed as plexiform neurofibroma.[1] It classically affects young adults aged 20–50 years[4] and is usually confined to the head and neck or trunk.[56] Plexiform schwannoma typically presents as a mobile, solitary, smooth-surfaced, and nontender mass.[7] It shows slow growth and single attachment at the nerve of origin without pain or neurologic symptoms. If pain or neurologic symptoms are present, they are usually associated with a mass effect.[8] In spite of the fact that they are common in the head-and-neck region, the involvement of the lip is considered to be extremely rare.[9] Histologically, schwannomas are divided into the following seven subtypes: classical (Verocay), plexiform, cellular, cranial nerve, melanotic, degenerated (ancient), and granular cell schwannomas.[10]

The diagnosis of lip schwannomas is typically made following biopsy and it demonstrates cytologically bland spindle cells in hypercellular Antoni A and hypocellular Antoni B patterns. Scattered, dilated, and focally thrombosed blood vessels are visualized which are a feature of these lesions.[11] Intense S-100 protein immunoreactivity for cytoplasmic and nuclear patterns indicates neural origin. These staining-associated light microscopic findings confirm the diagnosis of plexiform schwannoma.[7] Surgical resection is the mainstay of treatment.[2]

Case Report

A 16-year-old boy presented to our clinic for evaluation of a painless swelling of the lower lip. He had no history of trauma or systemic disease. The patient had noted the swelling of the lower lip for about 1 year but had not sought treatment because the lesion was symptom free. When the lesion did not resolve, he was referred for diagnostic evaluation. Oral examination revealed a painless swelling of the lower lip measuring 7 mm × 5 mm [Figure 1]. The swelling had an elastic consistency. It did not blanch on pressure and no pulsation could be felt. No tenderness and altered sensation were elicited. His dental and medical history was unremarkable. Mucocele, neurofibroma, granular cell tumor, and fibroma were the differential diagnoses of this mass. Excision of the lip lump was performed under local anesthesia and sent for histological staining and examination. Histopathologic analysis revealed multiple, circumscribed foci surrounded by a thin band of collagen composed of fascicles of spindle-shaped cells with palisaded nuclei and Verocay bodies [Figures 2–4]. In addition, immunohistochemical (IHC) study was positive for S100 protein, SOX10 antibody, scattered positive for CD34, and negative for epithelial membrane antigen (EMA) and glial fibrillary acidic protein [Figure 5]. The final diagnosis of our case was plexiform schwannoma. Postoperative time was uneventful and the patient has been remaining disease free after 9 months of follow-up period [Figure 6].

Figure 1

A 7 mm × 5 mm, well-circumscribed soft-tissue swelling in the lower lip

Figure 2

Circumscribed, encapsulated, multiple interlacing and interconnecting fascicles and dermal tumor (H and E, ×40)

Figure 4

Verocay body formations (eosinophilic masses and rows of nuclei) (H and E,×400)

Figure 5

Immunoperoxidase staining, ×200, demonstrating the typical staining

Figure 6

Postsurgery image

Circumscribed foci surrounded by a thin band of collagen composed of fascicles of spindle-shaped cells with palisaded nuclei (Antoni A) (H and E, ×100)

Discussion

Plexiform schwannoma has received its name since the Schwann cells are arranged in a plexiform pattern in the dermis and subcutaneous layers. Nevertheless, this neoplasm can be found deep to those layers near any peripheral nerve throughout the body. It typically affects patients aged 1–61 years, with a strong preponderance in young adults aged 20–50 years.[4] The head and neck are frequent sites for schwannoma as 25%–45% of all Schwannomas occur in these areas, but lower lip is quite an uncommon site for its development.[2812] A literature search in MEDLINE revealed only five documented cases of lower-lip schwannomas. The patients were between the ages of 7 and 72 years and most of them were male. The main therapeutic procedure was surgery but one case underwent surgery and radiotherapy. Follow-up period of patients was between 6 weeks and 37 months [Table 1].

Table 1

Cases of lower lip plexiform Schwannomas

Authors	Published year	Age	Gender	Treatment	Follow-up period
Baderca et al.[2]	2008	25	M	Surgery	Not available
Lobo et al.[10]	2009	7	M	Surgery	9 months
Jurkovic et al.[15]	2009	72	M	Surgery and radiotherapy	37 months
Cardoso et al.[16]	2010	52	M	Surgery	12 months
Dhua[7]	2015	18	F	Surgery	6 weeks
Present case	2018	16	M	Surgery	6 months

M: Male; F: Female

The etiology is unknown and the tumor is generally asymptomatic. Schwann cell tumors can remain quiescent for a long period and sometimes they are found incidentally. Pain and neurological symptoms are uncommon, unless the tumors become large or they invade submucosal locations.[2] The differentiation between schwannoma and neurofibroma is essential because apparently “solitary” neurofibroma may be a manifestation of neurofibromatosis.[2]

The histological features of plexiform schwannomas are similar to conventional schwannoma, but there are multiple encapsulated nodules which vary in size and shape, separated by hyalinized fibrous stroma. The neoplasm mainly consists of Antoni type A tissue, composed by cells with small spindle or wavy nuclei arrayed in cellular fascicles often with nuclear palisading.[10] Immunohistochemistry of schwannoma demonstrates positive S100 and negative EMA. Other IHC markers in the diagnosis of schwannomas are CD34 and vimentin.[13] There are variants of benign schwannomas such as plexiform or multinodular, cellular, Wagner–Meissner, granular cell, and nerve sheath myxoma neurothekeoma. Preoperative diagnosis of lip schwannoma can be made by ultrasound, computed tomography, and magnetic resonance imaging, but these are not routine or necessary.[11] For our case, diagnostic imaging was not performed and the diagnosis was made by histological study.

The management of a benign solitary schwannoma is enucleation and all efforts have to be made to protect the nerve of origin and function. The relative avascular character of the neoplasm permits the dissection within the capsule and the separation from parental nerve. Lip schwannoma can be pathologically misleading and resemble malignancy. Malignant transformation is rare, observed in 8%–10% of isolated tumor cases. Only three cases of recurrent malignant lip schwannoma have been documented, but recurrence is unlikely with complete resection.[21114] If recurrence occurs, it needs to consider whether complete enucleation is achieved or malignant transformation is a possibility.[11] In general, the prognosis of schwannoma is quite favorable.[14]

In conclusion, this rare entity in the lower lip must be considered by the clinician during the evaluation of a lower lip swelling.

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Conflicts of interest

There are no conflicts of interest.