Oral lipoma: Many features of a rare oral benign neoplasm

Introduction Lipomas are common benign soft tissue neoplasms composed of mature white adipocytes. They are the most common soft tissue mesenchymal neoplasms. However, they are relatively uncommon in the oral and maxillofacial regions. Their overall incidence in the oral cavity is thought to be between 1% and 4% of all benign oral lesions. Specific anatomic locations within the oral and maxillofacial region include the parotid region, buccal mucosae, lips, submandibular region, tongue, palate, floorof-mouth and vestibule. Infrequent locations of orofacial lipomas include the maxillary bones, especially the mandible. Among lipomas, different subtypes can be described: simple lipoma, lipoma with chondro-osseous metaplasia, chondroid lipoma, fibrolipoma, infiltrating lipoma, angiolipoma, myolipoma of soft tissue, angiomyolipoma, spindle cell/pleomorphic lipoma (SCL/PM), myxolipoma, angiomyxolipoma, dendritic myxofibrolipoma, sialolipoma, congenital lipoma, hibernoma and atypical lipomatous tumor (ALT). Case Report We report an unusual large-sized lipomatous tumor located on the left side of floor-of-mouth, one of the rarest sites of intraoral lipoma. The final diagnosis of the lesion was fibrolipoma. The unusual characteristics of this case report were the large-sized dimensions of the neoplasm, which were 3 cm along the main diameter, and the histological subtype which is not common among the lipomas of the floor-of-mouth and of the oral cavity in general Conclusion A histological examination after removal of lipomas is imperative to exclude liposarcomatous degeneration. A detailed revising of the subtypes classification of the benign lipomatous tumours of the oral cavity is provided in this paper. Introduction Lipomas are common benign soft tissue neoplasms composed of mature white adipocytes. They are the most common soft tissue mesenchymal neoplasms1. They primarily affect the region of the trunk, shoulders, neck and axilla, with 15 to 20% of the cases involving the head and neck region. However, they are relatively uncommon in the oral and maxillofacial regions2. The overall incidence in the oral cavity is thought to be between 1% and 4% of all benign oral lesions3. Lipomas are more common in males than females, although several authors believe that there is not sex predominance4. Oral tumours generally occur in adult patients between the ages of 40 and 60 years, similar to other benign soft tissue lipomas. Lipomas are usually described as long-standing soft nodular asymptomatic swellings covered by normal mucosa. The first description of oral lipomas was provided by Roux in 1848 in a review of alveolar masses. He referred to it as a “yellow epulis”5. Lipomatous benign tumoural tissue is very similar to normal adipose tissue; however lipoma metabolism differs, as it has been shown that the fat tissue of lipoma is not used for energy production during starvation periods as occurs with normal adipose tissue. Specific anatomic locations within the oral and maxillofacial region include the parotid region, buccal mucosae, lips, submandibular region, tongue, palate, floorof-mouth and vestibule. Infrequent locations of orofacial lipomas include the maxillary bones, especially the mandible. Site predilection is most likely associated with the availability of adipose tissue, which is high in the buccal mucosa due to the proximity of the buccal fat pad and very low in the palate. The tumours are described as circumscribed, encapsulated, and firm to rubbery with a tan, yellow greasy cut surface. They appear as a single or lobulated long-standing painless lesion with either a sessile or a pedunculated base3. A characteristic feature is a change in consistency and form of the lesion during contraction of involved muscle. The mean tumour size according to the literature is 2.2 centimetres2. Oral lipoma is diagnosed more frequently at a mean age of 50 to 62 years. The duration of lipomas ranges from 2 to 84 months, with a mean of 30.4 months. No consensus exists regarding the pathogenesis of oral lipomas. Currently, heredity, fatty degeneration, hormonal basis, trauma, infection, infarction, metaphase of muscle cells, lipoblastic embryonic cell nest in origin and chronic irritation are probable representative theories to elucidate *Corresponding author Email: [email protected] 1 Department of Surgical and Morphological Sciences, University of Insubria, Ospedale di Circolo Macchi Foundation, Unit of Oral Pathology, Varese, Italy 2 Department of Surgical and Morphological Sciences, University of Insubria, Ospedale di Circolo Macchi Foundation, Unit of Pathologic Anatomy, Varese, Italy 3 Department of Biomedical, Surgical and Dental Sciences, University of Milan, Ospedale Maggiore Policlinico IRCCS Ca' Granda Foundation, Unit of Oral Pathology and Medicine, Milan, Italy