An Unusual Intraoral Lipoma: A Case Report and Literature Review

Background

Lipoma is a painless tumor derived from mesenchymal connective tissue, composed mainly of mature adipocytes. It manifests in soft tissue and has slow and circumscribed growth. In relation to the whole body, it is possible to differentiate between superficial lipomas which are subcutaneous, deep-seated lipomas which occur under the enclosing fascia, and a less common form which arises within muscles – intramuscular lipomas [1]. The differential diagnosis of lipomas can be between different conditions such as: epidermoid cysts, hematomas, panniculitis, and other forms of adipocytic tumors (Table 1). Occurrence is relatively rare in the oral region, with percentages fluctuating between 1% and 4% [2]. Oral lipomas can manifest as deep nodules with a regular surface color. In such circumstances, salivary gland tumors and benign mesenchymal neoplasms should also be considered in the differential diagnosis [3]. Locations most commonly affected are the buccal mucosa, upper and lower lips, palate, tongue, buccal sulcus, floor of the mouth, and salivary glands [4,5]. Histologically, they are composed mainly of mature adipocytes, while the malignant counterpart presents low levels of differentiation and is defined as liposarcoma. Liposarcomas, although the predominant form of mesenchymal tumors in the body, are rare in the oral cavity, with very few reported cases, predominantly in the buccal mucosa and floor of the mouth [6]. They can also appear as an intermediate, low-grade lipomatous neoplasm defined as atypical lipomatous tumors/well-differentiated liposarcoma (ALT/WDLPS), which is non-metastasizing, but can dedifferentiate and become malignant [7]. In 2013 the WHO created a Classification of Soft Tissue Tumors, in which the different adipocytic tumors are listed, including 11 benign sub-types, 1 intermediate category, and 5 categories of malignant fatty neoplasms (Table 2) [8]. Lipomas can be found at different depths within a tissue, but are always capsulated, and can present as sessile, pedunculated, or submerged. Lipomas usually occur as solitary lesions and can vary from small well-rounded lesions to large, poorly-defined, lobulated masses. When the clinical manifestation appears as multiple lesions, it may be connected to syndromes such as neurofibromatosis, Gardner’s syndrome, Dercum’s disease, familial multiple lipomatosis, Proteus syndrome, or Cowden syndrome, which is due to mutations in the PTEN gene and is associated with multiple lipomas, facial trichilemmomas, oral papillomas, punctate palmoplantar keratosis, and a diversity of malignancies [9]. The color is usually yellowish, but varies depending on the thickness of the overlaying mucosa.

Because it is a painless lesion, a patient can have an intra-oral lipoma for years without noticing it. In the present case, the main problem was initial trauma and speech difficulty due to the size of the tumefaction. One main problem, especially in this case, is the possibility of a continuous trauma from mastication, with possible keratosis and further complications. In the present case of a giant intraoral lipoma, the site of the lipoma was unusual and it grew to over 2 cm, making it an atypical clinical entity [10].

Case Report

A 46-year-old man was referred to the Department of Oral and Maxillo-Facial Sciences of “Sapienza”, University of Rome, with a complaint of a large mass impeding speech and causing discomfort when chewing. The patient presented with hypercholesterolemia during medical anamnesis, but no other systemic or medical condition was noted. He had no history of smoking or substance abuse. Extraoral examination revealed no alteration of vertical nor horizontal symmetry (Figure 1). Instead, oral examination revealed a large mobile mass in the left buccal mucosa (Figure 2). Measurements showed a 2.5×2 cm oval mass. The mass was soft and had a normal pink-colored mucosa overlay, and no pain was felt by the patient during examination. The treatment consisted of a vertical surgical incision with a Bard-Parker #15 C blade under local anaesthesia on the mucosa at the maximum height of the tumefaction (Figure 3). Peripherical dissection with Metzenbaum scissors (Figure 4) allowed separation of the lesion capsule from the surrounding tissue, and applying external pressure permitted the avulsion of the lesion from its site (Figure 5). The surgical incision (Figure 6) was then sutured with 3.0 Vicryl (Ethicon, polyglactin 910, braided absorbable suture, 3/8, cutting edge) along the line of the incision (Figure 7). The excised lesion was 2.5×2 cm (Figure 8).

Histological examination with hematoxylin and eosin staining revealed mature adipocytes without atypia, consistent with a lipoma. The suture points were removed on the 7th day after surgery (Figure 9). A further check was made on the 14th day to ensure proper healing (Figure 10).

Discussion

The buccal mucosa has abundant fatty tissue and thus is the most common site of intraoral lesions [4,5]. Areas such as the tongue and hard palate are less commonly affected because they have less fatty tissue. Studart-Soares et al. [11] reviewed 450 cases of intraoral lipomas and found that the most common site was the buccal mucosa (n=174; 38.7%), followed by the vestibule (n=35; 7.8%), retromolar area (n=21; 4.7%), and other sites (n=220; 48.8%). They found no significant difference between males and females with respect to lesion distribution: 256 were males (52.2%) and 234 were females (47.8%). A study by Taira et al. reviewed 207 cases and found that the buccal mucosa was the most common site (n=84, 40.6%), followed by the tongue (n=37, 17.9%), lips (n=26, 12.6%), and other areas (n=60, 28.9%), and found no significant sex distribution difference [12]. People in their 4th to 6th decades of life were most commonly affected [11–13]. The etiology and pathogenesis remain unclear, although endocrine, mechanical, inflammatory, hypercholesterolemia, and obesity factors are reported be associated with lipomas [13]. In the present case, the lipoma was located at the most common site but it was unusually large, and it is fortunate that it was removed before there was any important trauma to the overlaying mucosa. There were no surgical complications, but we had to suture the flaps tightly to avoid trauma because the slow-growing mass created a larger area of mucosa, which, if not tightly secured with the suture, could droop and be traumatised through chewing.

One possible risk in having such a large mass in the oral cavity and subjecting it to trauma is a possible degeneration of the histopathological features, leading to similar ALT-like characteristics. Differential diagnosis between other adipocytic tumors is through histologic examination and gene sequencing [14]. There are 4 types of histological variants of ALT/WDLPS, of which the adipocytic variant (lipoma-like) is the most common. ALT/WDLPS are a form of adipocytic tumor that uncommonly arises in the buccal cavity. Its danger lies in the possible dedifferentiation of the adipocytes, leading to malignancy. Histologic observation and immunohistochemistry help make the correct classification and diagnosis [15].

Conclusions

Lipomas are often unnoticed by the patient, and the main problems are self-inflicted trauma due to the bulge, which interferes with the normal chewing, and aesthetic problems. The only possible treatment is surgical excision of the lesion along with its capsule. Recurrence is rare, but an aggressive excision might perforate the encapsulating membrane and create a spill of cells, which might lead to recurrence. It is important to approach the lesion with a firm but non-aggressive incision and to perform the peripheral dissection with Metzenbaum scissors in order to free the lesion from the surrounding tissues. Due to its benign nature, the lesion does not generally need any further radiotherapy or chemotherapy [1].