Case Report: Rare site for intraoral meningioma

Extracranial meningioma is very rare with few cases reported, especially in the oral cavity. Its diagnosis is considered a challenge owing to the unusual site of occurrence. We report, to the best of our knowledge, the first case of extra-cranial meningioma as a primary tumor in the hard palate with no detected intracranial extension. A 59-year-old Egyptian female patient presented with a 22-year history of a large painless swelling at the right side of the hard palate, which could not be seen on radiographs. An incisional biopsy was taken and, after assessment with a panel of immunohistochemical markers, the lesion was diagnosed as extracranical grade I mengiothelial meningioma. The patient did not show up for surgical excision and follow-up was not performed because of the lose of contact with the patient. Intraoral meningioma is a rare tumor. Immuohistochemical markers are important for confirming this diagnosis.


Introduction
Meningioma is a benign neoplasm of meningothelial cells 1 . Meningioma may develop as a direct extension of a primary intra-cranial meningioma or as a true primary extra-cranial meningioma 2 .
Extra-cranial (ectopic) tumors are mostly seen in the head and neck region with no connection intra-cranially 3 . The most common extra-cranial site is the orbits. Meningioma arising in the oral cavity is extremely rare 4 . To the best of our knowledge, 19 cases have currently been reported in the oral cavity 2,4-20 and we are reporting the first case in the hard palate.

Case report
A 59-year-old female patient presented to the outpatient clinic in the Oral and Maxillofacial Surgery Department, Cairo University in January 2019 complaining of a large painless swelling in the hard palate ( Figure 1). The patient reported that the swelling had been present in her oral cavity for 22 years. The patient's medical and familial histories were unremarkable. As well as there was not a history of exposure to radiation. Upon clinical examination on the day of admission, a large hard palatal swelling (3 cm × 3 cm) was evident on the right side of the hard palate. The swelling was covered by normal mucosa and showed a slight bluish tinge. A provisional diagnosis of a benign peripheral nerve neoplasm and a minor salivary gland benign neoplasm were made. CT scan was performed with no evidence of bone involvement.
An incisional biopsy of the lesion was performed. Hematoxylin and eosin stained sections revealed meningothelial cells arranged in lobules. The cells exhibited round to oval nuclei ( Figure 2). Psammoma bodies were also present ( Figure 3). No mitotic activity and no cellular atypia were found. Immunohistochemical staining for tumor-associated markers was performed to confirm the diagnosis of meningioma and to exclude other mimic tumors as metastiatic carcinomas, schwannoma, neurofibroma, paraganglioma and perineurioma. Cells were positively stained using primary antibodies for epithelial membrane antigen (EMA) and vimentin (Figure 4a, b), but were not stained when using primary antibodies for S100, pancytokeratin, p63, chromogranin and renal cell carcinoma glycoprotein (Figure 5a-e).
No therapy was administered to the patient during her admission. Unfortunately, the patient did not show up for surgical excision and follow-up.

Amendments from Version 1
We have corrected grammar and language mistakes. We have added a new reference and changed the numbering of citations and added the data to text. We have added some lesions to the differential diagnosis list and discussed them.

Discussion
Primary extra-cranial meningioma is an unusual tumor, especially in the oral cavity 4 . The first intraoral meningioma reported was by Brown et al. in 1976, which presented as a periapical radiolucency in the anterior maxillary region 5 .
To the best of our knowledge, 19 cases of primary meningioma in the oral cavity have been reported. Of these, 13 were in female patients, which is also true of the present case. However, the age range was wide in the reported cases -between 10 and 77 years old 2,4-20 ; in the present case, the patient was 59 years old. Regarding the reported cases of intraoral primary meningioma, 6 of the 18 were in the maxilla 2,4-6,9,16 , 10 were in the mandible 7,10-15,19,20 , 2 in the buccal mucosa 17,18 and one in soft palate 8 . To the best of our knowledge, we report the first case in the hard palate.
The histopathological criteria of extracranial meningiomas are similar to those of their intracranial counterparts. All documented cases shared the same characteristics: whorls of spindle cells or epithelioid cell proliferation and psammoma bodies. In our case, diagnosis was challenging because of the tumor's similarity with other tumor entities of peripheral nerve origin, as well as the uncommon location of the tumor. An immunohistochemical panel of tumor-associated markers was used to confirm the diagnosis and to avoid unnecessary aggressive treatment. Most of the 19 cases reported in the literature were diagnosis using immunohistochemical markers. All reported cases that used immunohistochemistry techniques to diagnose meningioma 4,9-11,13,14,16,17,19,20 observed that the tumor cells stained positive for monoclonal antibodies against EMA and vimentin, with no immunoreactivity for S-100 protein, which was similar to our findings. However, EMA and vimentin are not useful to differentiate between meningioma and perineuroma as they both express positivity for EMA and vimentin but perineuroma the cells are spindle and elongated however, in our case they are rounded and polyhederal (meningiothelial pattern).
Unfortunately, our patient did not show up for surgical excision and follow-up was not done because of the loss of contact with the patient. However, most of the documented cases were treated successfully without recurrence by surgical excision. Some of the studies, such as that by Rommel et al. 20 , preferred only to follow-up with the patient rather than conduct surgical intervention. However, others preferred to perform aggressive treatment, such as as segmental mandibulectomy or segmenal resection 7,12 In conclusion, meningioma is a rare intraoral benign neoplasm. Immunohistochemical markers are an important tool to achieve a final diagnosis, especially for the differentiation from histological mimic entities of peripheral nerve origin,such as perineurioma and neurothekeoma and to avoid unnecessary aggressive treatment. Vimentin and EMA are the two important markers to confirm extra-cranial meningioma diagnosis.

Data availability
All data underlying the results are available as part of the article and no additional source data are required.

Consent
Written informed consent for publication of their clinical details and clinical images was obtained from the patient. The case report presents an extracranial meningioma of the hard palate. The patient's gender is conformed to the tumor but there are (likely) no contributing or risk factors associated with its occurrence. The lesion is asymptomatic and incisional biopsy was examined routinely and certain microscopic features were suggestive of meningioma. The specimen was further stained with a panel of markers and was diagnosed as meningioma of the palate. Unfortunately the patient did not return for surgical removal. Is the background of the case's history and progression described in sufficient detail?

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The patient's background can be improved if relevant findings are reported such as previous exposure to radiation as a potential risk for development of meningioma. Are enough details provided of any physical examination and diagnostic tests, treatment given and outcomes?
Expect the unexpected when similar lesions are encountered. 1.
Suggest an effective strategy to ensure patient's return when the outcomes are suspicious.

2.
excluded because the lesion is single and been present in her oral cavity for 22 year. 3-Discussion is fine although it would've been beneficial to cite the other reported palatal lesions. 4-The immunohistochemistry test panel discussion was added 5-Benign salivary gland neoplasm add to the list of lesions to be included in a general dentist's record when similar cases are detected. 6-English language corrections were done. 7-Conclusions were also corrected to include the consequence of wrong diagnosed.
Thanks again for your comments which add a lot to our knowledge and for your time too