Ancient Schwannoma of the Hard Palate Accompanied by Hyponatremia: A Unique Case ReportNima Nikafshar1, Mojde Masoudi2, 3, Siavash Vadaye Kheiri2, 3, Maryam Johari4*1. Private Dentist, Oral Medicine Specialist, Babol University of Medical Sciences, Babol, I.R Iran 2. Student Research Committee, Babol University of Medical Sciences, Babol, I.R. Iran 3. Oral and Maxillofacial Surgery, Babol University of Medical Sciences, Babol, I.R. Iran 4. Oral Health Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, I.R. Iran*Corresponding Author: Maryam Johari, Oral Health Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, I.R. Iran/ johari.mrm@gmail.comKey Clinical MessageThe present case is a unique type of schwannoma presenting pain and uncommon location in a hyponatremic patient. Given that the gold standard treatment for the lesion is excisional surgery, proving the possible association between hyponatremia and neural neoplasms could help with timely diagnosis and appropriate treatment and reduce complications.AbstractBackground and Objective: Schwannoma is a benign neurogenic neoplasm originating from the Schwann cells within the peripheral nervous system. Its incidence is documented at about 25%-45%, Yet its occurrence in the oral cavity is less than 12%. Given that neurogenic neoplasms are a well-documented but uncommon reason for hyponatremia, this is a case report of ancient Schwannoma of the palate, perforating the nasal floor, in an 80-year-old female along with hyponatremia.Case Presentation: An 80-year-old female presented with painful swelling in the anterior maxilla and the nasal floor. She had a history of hyponatremia, high blood pressure, tachycardia, and hypothyroidism. Clinical examination revealed apparent swelling in the buccal vestibule and the midline of the hard palate; the lesion had perforated \RL the palate to the nasal cavity\RL. CBCT radiographs revealed swelling of the soft tissue and erosion in the underlying bone. An excisional biopsy surgery was performed by laser. Microscopic examination showed spindle cell neoplasm composed of cellular areas (Antoni A), nuclear palisading (verocay bodies), and pauci-cellular microcystic areas (Antony B). Some tumoral cells showed nuclear atypia including nuclear enlargement with hyperchromasia with irregular border. Given that, the definitive diagnosis was an ancient Schwannoma.Conclusion: The present case is a unique type of Schwannoma, placed in an uncommon location. It presented pain and more importantly, perforated the hard palate to the nasal cavity.1. IntroductionSchwannoma or neurilemmoma is an uncommon neurogenic neoplasm originating from the Schwann cells within the nervous system. This tumor shows a strong affinity for the head and neck. Also, its incidence is documented at about 25%-45% (1), Yet its occurrence in the oral cavity tract is less than 12% (2). Schwannoma is the most frequent tumor of the peripheral nerve sheath. They are also benign, almost asymptomatic, and well-circumscribed tumors that grow slowly with the peripheral nerves. Moreover, they are commonly solitary tumors (3) on the floor of the mouth or tongue, but their presence in the hard palate is relatively rare (2). Ancient Schwannoma was first described by Ackermann and Taylor as a persistent Schwannoma with degenerative diversions like calcification, cystic formation, tissue necrosis, xanthomatous alterations, vascular hyalinization matrices, and noticeable nuclear atypia, attributed to the tumor growing (4, 5). \RL Besides the ancient type, there are other types such as plexiform, cellular, and epithelioid (6). Immunohistological examinations can be useful in the differential diagnosis of schwannoma from other mimicking lesions (3). Hyponatremia is the most frequent electrolyte disorder and happens when serum sodium concentration is less than 135 mmol/L. Neurogenic neoplasms are a well-documented but uncommon reason for this disorder (7). Although few cases indicate a relationship between schwannoma and hyponatremia (7, 8), it is yet to be discussed, especially in this location. In the current study, we report a rare case of ancient schwannoma of the palate, perforating the nasal floor in an 80-year-old female along with hyponatremia.2. Case presentationAn 80-year-old woman \RL came to an oral medicine specialist in 2023 with the chief complaint of pain in the anterior maxilla and the nasal floor. She had a history of hyponatremia, high blood pressure, tachycardia, and hypothyroidism. In the extra-oral clinical examination of the patient, swelling was observed in the soft tissue of the anterior maxilla and the floor of the nasal cavity (Figure1). Intraoral examination revealed an apparent swelling in the buccal vestibule as well as the midline of the hard palate (Figure2). \RL This lesion was 4x4 mm, lobular, and had a rubber consistency. In the periapical radiograph of the edentulous area (Figure3), no obvious pathology was seen inside the bone. Therefore, a Cone Beam computed Tomography (CBCT) was prepared from the target area for further investigation. In the CBCT images in different plans, the alveolar bone of the anterior maxilla was sound and intact, But the swelling in the soft tissue of the nasal cavity floor was clear (Figure4). In the area of the hard palate, swelling of the soft tissue was seen along with erosion in the underlying bone (Figure5). This lesion perforated the palate to the nasal cavity. According to the radiographic appearance and use of removable complete dentures by the patient, the diagnostic hypothesis was irritating fibroma for the lesion of the hard palate and nasolabial cyst for the anterior maxilla lesion. An excisional biopsy of the lesion was performed by laser11Light amplification by stimulated emission of radiation and the specimen was sent for pathological examinations in formalin. The received specimen consisted of 2 pieces of creamy tissue measuring 2*1*1cm and 0.7*0.7cm and a rhomboid piece of skin tissue 1*0.7cm. Microscopic examination of the received specimen showed spindle cell neoplasm composed of cellular areas (Antoni A), showing nuclear palisading (verocay bodies) and pauci-cellular microsystic areas (Antony B). Miotic activity was not appreciated. Some tumoral cells showed nuclear atypia including nuclear enlargement with hyperchromasia with irregular border. No necrosis was noted (Figure6). The immunohistochemistry analysis was performed and following markers were evaluated: S100 and SOX10 were diffusely positive, CD34 was positive in few cells, SMA and DESMIN were negative and analysis of Ki67 showed low proliferative index. Therefore, the definitive hypothesis was ancient schwannoma. Based on the review of articles in which the association of schwannoma in the mediastinal area and hyponatremia was observed, neurology consultation and brain CT were prescribed. The one\RL-year follow-up showed no recurrence \RL (Figure7).3. Differential DiagnosisDifferential diagnosis for the present lesion could include a number of benign neoplasms. The most likely diagnosis could be benign tumors of salivary glands such as adenoma. fibroma and, lipoma are other possibilities which are respectively benign tumors of connective tissue and adipose tissue. Residual cystic lesions could appear similarly. malignant neoplasms such as oral squamous cell carcinoma of the bone and salivary gland carcinoma, could rarely s how benign manifestations (9). There are so many systemic conditions associated with hyponatremia that can cause oral lesions as well. Congestive heart failure can lead to hyponatremia and fluid overload that can cause edema in the face and oral cavity potentially mimicking an oral mass. Hypothyroidism is also associated with hyponatremia due to impaired water excretion which can lead to myxedema. On the other hand, patients with hypothyroidism have an increased risk of developing benign tumors in the oral cavity. Adrenal insufficiency can lead to electrolyte imbalances and various oral manifestations and hyperpigmentation of the oral mucosa which might be mistaken for an oral mass (10).4. DiscussionAs was discussed, schwannoma is benign and usually asymptomatic, but its etiology is still unknown (11). Moreover, schwannoma of the oral cavity is most presented in the soft tissue, especially the tongue, and intraosseous tumor is the most rare location for it (12). Given that the current case is located in the hard palate and perforated the nasal floor, it is almost unique. Ancient schwannoma can be presented in all ages, but it is more regular between the age of 10-40 years old, affecting women slightly more (2). In this case, the lesion occurred in an 80-year-old female, which is somehow noticeable. The presence of pain or other discomforts is not common but related to the location toward the nerve or the size of the lesion. The absence of symptoms can be a reason for the transformation to the ancient type (2). In this case, pain was a chief complaint, unlike many other cases. Song et al. (7) reported the resolution of hyponatremia after the removal of schwannoma. In the current study, the patient is suffering from ancient schwannoma along with hyponatremia, As a result, the possibility of an association between these two conditions should be investigated in future studies. From the histopathological aspect, this tumor is composed of spindle cells along with eosinophilic cytoplasm and a round to oval nucleus noticeable on cellular areas, as Antoni A, and myxoid with hypocellular areas as Antoni B. Verocay bodies are also eosinophilic formations as a characteristic mark In the Antoni A fields (2, 13). Antony A, Antony B and verocay bodies were obvious in this case, like many other cases. Also, nuclear atypia including nuclear enlargement, hyperchromasia, and irregular border were other noteworthy findings of this case. Thus, immunohistochemistry analysis was performed to avoid misdiagnosis. Immunohistochemical analysis is a valuable approach to confirm the diagnosis. In this case, S100 was diffusely positive, like the case of Kardouni et al. (4), as a marker of focal spindle-shaped cells. They also recognized CD68, as a marker of histiocytes. Moreover, According to the Gainza-Cirauqui et al. report (2), the CD34 marker is usually negative, in contrast to this case. The gold standard treatment for this tumor is complete excision surgery (2). According to Kardouni et al., no ancient Schwannoma of the oral cavity has been shown malignant transformation (2), as was this case.5. ConclusionAncient \RL Schwannoma is usually a benign tumor, thus the presence of pain as well as nasal perforation in this case is noteworthy and indicates the importance of timely diagnosis and appropriate treatment. Given that ancient Schwannoma, especially in this location, is uncommon and also considering the manifestation of pain, which is not common, the necessity of careful investigation of similar cases is felt so that surgical intervention can be performed at the right time and possible complications can be avoided.References1. 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