Lingual Osseous Choristoma: A Case Report and Review of the Literature

Choristoma is defined as the proliferation of normal tissue in an abnormal anatomical location. Although choristomas are usually asymptomatic, it is important they recognize them as they may clinically mimic neoplasms when they give symptoms. Choristomas located in the oral cavity may consist of various tissues such as bone, cartilage, glial tissue, gastric mucosa and sebaceous glands [1]. Osseous choristoma is a benign lesion that develops with the proliferation of mature bone tissue in an abnormal region in which bone tissue is not normally found. This entity was first defined in 1913 by Monserrat as “lingual osteoma”. The term “osseous choristoma” was used by Krolls et al. in 1971 for the first time [2-3].


Introduction
Choristoma is defined as the proliferation of normal tissue in an abnormal anatomical location. Although choristomas are usually asymptomatic, it is important they recognize them as they may clinically mimic neoplasms when they give symptoms. Choristomas located in the oral cavity may consist of various tissues such as bone, cartilage, glial tissue, gastric mucosa and sebaceous glands [1].
Osseous choristoma is a benign lesion that develops with the proliferation of mature bone tissue in an abnormal region in which bone tissue is not normally found. This entity was first defined in 1913 by Monserrat as "lingual  Lingual osseous choristomas can occur at any age but the majority of the patients are in their second or third decades of life [4]. Among the cases reported in the literature, the youngest patient was 5 and the oldest was 73 (mean age: 25,2+14,8) [3][4][5]. There is a strong female predilection (F/M: 50/17). Our case is a 26-year-old male patient.
Osseous choristomas of the oral cavity and maxillofacial region are most frequently localized in the tongue. 88,2% of the cases, the lesion was located in the posterior one-third of the tongue, 7,4% in the middle one-third of the tongue, 2,9% in tongue lateral borders and 1,5% on the floor of the tongue. In addition, buccal mucosa, buccal vestibule, alveolar mucosa, submandibular region, submental region, retromolar region, masseter muscle and palate localization can be seen [6].
The etiopathogenesis of lingual osseous choristoma is not fully understood. There are two theories widely recognized to explain the development of osseous choristomas. These are the "embryological" and "post-traumatic" (reactive) theory. According to the embryological theory, the lesion develops from the pluripotent cells in the 1st and 3rd branchial arches. The post-traumatic theory is based on the fact that posterior one-third of the tongue is the most common site of traumatic irritation of the oral cavity. The theory suggests that local inflammation and calcium deposition months of follow-up there is no evidence of recurrence.

Discussion and Review of the Literature
We searched the literature in PUBMED, MEDLINE, Google Scholar and XXXXX Library database using the keywords "lingual", "osseous", "choristoma", "tongue", "lesion" and their combinations. We also examined the content and bibliography of all the available publications manually. Only the cases with the histopathological diagnosis of "lingual osseous choristoma" were included. The diagnosis of "osteoma" were excluded from the review. Our review revealed 77 lingual osseous choristoma cases reported between 1971 -2017 (  in the trauma site give rise to the lesion [7]. In our case, the lesion consisted of mature bone tissue with fully developed Haversian system and not just calcification. Also, there was no evidence of local inflammation in the surrounding tissue. We believe that post-traumatic theory alone is insufficient to explain the etiopathogenesis of lingual osseous choristoma. Osseous choristoma of the tongue is mostly asymptomatic (46%). In symptomatic cases, lump (31,7%) was the most common complaint. Additionally, gagging (9,5%), dysphagia (4,8%), pain (4,8%), nausea (1,6%) and throat irritation (1,6%) were the other symptoms reported [8].
Grossly, osseous choristomas are usually under one cm in size, pedunculated or sessile, well-demarcated, firm, smooth surfaced, gray-white, pink colored nodular lesions [9]. 67,2% of the osseous choristomas reported in the literature are pedunculated and 32,8% are sessile. The size of the lesion ranged from 2 to 20 mm and the mean size was 8,7+3,6 mm. In our case the patient was complaining of a lump and physical examination revealed a six mm sessile lesion.
Histopathologically, lingual osseous choristoma is submucosally located and consist of well-developed lamellar bone and Haversian system. Osteoblastic and osteoclastic activity, cytological atypia or mitosis are not observed in the bone tissue [10].
Differential diagnosis of lingual osseous choristomas should be made according to where the lesion is located on the tongue. For a lesion that is situated on posterior one-third of the tongue, lingual thyroid, thyroglossal ductus cyst, mucocele, pyogenic granuloma, hemangioma, lymphangioma, hamartoma, salivary gland tumors and sarcomas should be included in the differential diagnosis. Anterior and lateral localization should be differentiated from fibroma, granular cell tumor and neural origin tumors. Salivary gland tumors, mucus retention cysts, neural tumors and lipomas are differential diagnosis with osseous choristomas located under the tongue [11].
The treatment of osseous choristoma is the total excision of the mass. Recurrence after excision is not expected. In the literature, recurrence of two cases of osseous choristoma has been reported [12].
In conclusion, lingual osseous choristoma is a rare benign lesion. This lesion, which can be confused with benign and malignant tumors in the oral cavity and maxillofacial region, should be considered when a clinicopathological diagnosis is made. In this review, available cases of lingual osseous choristomas were gathered and our case is presented with the literature.