A rare presentation of lipoma on mandibular mucogingival junction.

Lipoma is the most common tumor of mesenchymal tissues of body, but its occurrence in oral cavity is infrequent. Buccal mucosa is the most common intraoral site of lipoma followed by tongue, floor of the mouth, and buccal vestibule. The involvement of mucogingival junction is rare. We present a unique case report of oral lipoma occurring on mandibular mucogingival junction with review of literature which has emphasis on differential diagnosis.

INTRODUCTION

Lipomas are most common benign neoplasms of mesenchymal tissues accounting for their 15–20% of cases occurring in head and neck region, while only 1–4% cases seen intraorally.[12] The etiology and pathogenesis of lipoma is not clear, but many factors such as mechanical, endocrine, and inflammatory influences have been reported inconclusively for their role.[13] In oral cavity, lipomas are observed during routine intraoral examination and usually involve areas with fat accumulation.[2] Clinically, lipomas are slow growing asymptomatic painless nodular swellings with either yellow color or that of normal mucosa.[2] Intraorally, most commonly involved sites are buccal mucosa, tongue, floor of the mouth, buccal vestibule, and lips.[34] We here present a rare case of lipoma occurring on mandibular mucogingival junction, an extremely rare intraoral site for lipoma with focus on differential diagnosis.

CASE REPORT

A 32-year-old male patient reported with the complaint of painless swelling in left mandibular posterior region since 4 months that was gradually increasing. The patient had no history of dysphagia, difficulty in speaking, and no previous episode of swelling in the same region. The patient had not undergone any treatment for the swelling and not taken any medication. There was no significant family and medical history. No obvious facial swelling or lymphadenopathy was observed. The intraoral swelling measuring 12 mm × 18 mm approximately was observed on the left mandibular mucogingival junction extending from the second premolar to third molar [Figure 1]. Swelling was of same color to that of normal adjacent mucosa. There was no pus or blood discharge from the swelling and no ulceration. On palpation, swelling was soft in consistency with smooth margins and not fixed to underlying deeper structures. A slight compressibility was observed in the swelling and was nontender. Intraoral periapical radiograph revealed normal trabecular bone structure and no pathological changes were observed in alveolar bone [Figure 2]. Based on the history and clinical examination, a provisional diagnosis of intraoral benign soft tissue tumor was given. It was surgically excised by excisional biopsy and was sent for histopathological examination. The hematoxylin- and eosin-stained soft tissue specimen showed the presence of sheets of mature adipocytes in a distinct lobular arrangement with a thin fibrous capsule [Figure 3]. The mature adipocytes demonstrated large clear cytoplasms and eccentric nuclei [Figure 4]. There was no evidence of cellular atypia. Based on the above findings, a final diagnosis of lipoma was made. The patient was recalled after 1 week for suture removal. The wound had healed uneventfully. No signs of recurrence were seen at a follow-up for 6 months.

Figure 1

Intraoral swelling in left mandibular posterior region

Figure 2

Intraoral periapical radiograph revealing normal trabecular bone pattern

Figure 3

Photomicrograph showing sheets of mature adipocytes in a distinct lobular arrangement with a thin fibrous capsule, A = adipocyte, C = capsule. (H and E, ×100, scale bar = 25 μm)

Figure 4

Photomicrograph showing mature adipocytes demonstrating large clear cytoplasms and eccentric nuclei, A = adipocyte, *represents blood capillary. (H and E, ×400, scale bar = 5 μm)

DISCUSSION

Lipomas are mesenchymal tumors of adipose tissue. They commonly involve trunk and proximal portions of extremities and are relatively uncommon in oral cavity. They account for 0.5–5% of all benign tumors of oral cavity.[12] The etiology is still not clear, but a role of various factors has been reported.[3] According to “hypertrophy theory” these tumors occur in oral cavity due to obesity and inadvertent growth of adipose tissue. However, it cannot explain lipomas occurring at sites devoid of fat. However, “metaplasia theory” states that aberrant differentiation ofmesenchymal cells into lipoblasts leads to the development of lipoma.[4] It is thought that trauma and chronic irritation may trigger the proliferation of fatty tissue that can cause development of lipoma.[5]

Mean age of occurrence of intraoral lipoma varies according to different studies, but they usually occur in fourth and fifth decades of life.[6] The occurrence of lipoma is uncommon in children.[7] Their prevalence is similar in both the sexes, although a male and female predominance has also been recorded.[45] The present case of lipoma was seen in a male patient with age of 32 years. Most common intraoral sites are buccal mucosa, tongue, floor of the mouth, vestibule, and lip. In a study by Taira et al., lipoma on gingiva was found in only 8.7% of the cases out of 207 cases of oral lipoma, suggesting it to be an uncommon site of occurrence.[8] Manor et al. could not document any case of gingival lipoma in an analysis of 58 cases of oral and maxillofacial lipomas.[9] Studart-Soares et al. had documented gingiva to be the rarest intraoral site for lipoma in their extensive analysis of 450 cases of lipoma.[10] Dattilo et al. also had reported the periodontium to be a rare site of intraoral lipomas.[11] A case of lipoma occurring on mandibular mucogingival junction was recently reported.[12]

Oral lipomas clinically may present as slow growing solitary or multiple lesions which may be sessile or pedunculated.[15] They present as asymptomatic, well-circumscribed soft encapsulated fluctuant masses or nodules with doughy consistency.[2] Grossly, the color may vary from that of normal mucosa to pink and some may present as yellowish masses. The diagnosis is not easy if the yellow color of the tumor is not visible through overlying thin mucosa.[13] Size of the tumor varies and depends on the location. In a study, size as large as 8 cm has also been reported.[7] Although the growth of oral lipomas is usually limited, they can reach great dimensions, interfering with speech and mastication, reinforcing the need for excision.[2] In our case, the patient presented with a solitary soft sessile smooth mass measuring 12 mm × 18 mm approximately. The complications typically associated with lipomas have been functional impairment due to giant size that they achieve occasionally. No neurological complications have been reported yet.

Because of the similar clinical presentation, lesions such as oral dermoid and epidermoid cysts, oral lymphoepithelial cyst, benign salivary gland tumor, mucocele, benign mesenchymal neoplasm, ranula, ectopic thyroid tissue, and lymphoma are considered in its differential diagnosis. In our patient, the possibility of fibroma was excluded as the swelling was soft in consistency. The possibility of a dermoid or epidermoid cyst was also excluded as the location was not in favor. Hemangioma, lymphangioma, rhabdomyoma, neuroma, or neurofibromas are the swellings to be ruled out when tumor is located on dorsal surface of tongue.[4] Although oral lipomas are well-circumscribed soft tissue lesions, rarely they give a radiographic impression of an intraosseous neoplasm within the mandibular canal.[14] Lipomas may show radiographic features rarely manifesting as radiolucency.[10] The gross specimen of lipoma when placed in a pot with water usually floats in it.[3] It is difficult to distinguish lipoma from surrounding connective tissue when it is deeply placed. Fine-needle aspiration biopsy (FNAB) or Ultrasound –guided FNAB sometimes can be used for aspiration in such cases. Ultrasonography is a preferred technique as it is faster and inexpensive, and lipomas are hypoechoic with echogenic spots.[15] Magnetic resonance imaging can be used to find the anatomical extent of intraoral tumors.[15] A color Doppler ultrasonography can also be done to evaluate the content of the lesion and its vascularity.[15] The prognosis of oral lipomas is good and recurrence rarely occurs.

Histopathology remains the gold standard in the diagnosis of lipoma. The histopathological features constitute of a circumscribed aggregate of mature adipocytes which may be encapsulated. Adipocytes show large clear cytoplasm in the absence of vascularity which serves as diagnostic feature of classic lipoma.[6] All lipomas are usually well-vascularized, but the vascular network is compressed by the distended lipocytes and is usually not appreciable.[16] The hematoxylin- and eosin-stained soft tissue specimen in our case showed the presence of mass of mature adipocytes arranged in lobules surrounded by a fibrous capsule. Adipocytes have large empty cytoplasms with eccentrically placed nuclei. There was no evidence of cellular atypia. On the basis of microscopic features, lipomas can be classified as simple lipoma, fibrolipoma, infiltrating or intramuscular lipoma, angiolipoma, myxolipoma, spindle cell lipoma, pleomorphic lipoma, myolipoma, angiomyolipoma, chondroid lipoma, osteolipoma or ossifying lipoma, and salivary gland lipoma (sialolipoma).[2] Histopathologically, the differential diagnoses are normal soft fatty tissue, other histologic variants of lipoma and liposarcoma.[6] Other lesions which should be distinguished are schwannoma, myxoid neurofibroma, leiomyoma, nodular fasciitis, myxolipoma, fibrolipoma, malignant fibrous histiocytoma, myxoid liposarcoma, and myxoid solitary fibrous tumor.[15] Despite the close histological similarity to normal adipose tissue, lipomas, usually, have chromosomal aberrations such as translocations involving 12q13-15, locus interstitial deletions of 13q, and rearrangements involving 8q11-13 locus.[17] Immunohistochemistry has been used for differentiation between benign and malignant adipose tissue tumors with detection of aP2, a protein expressed by lipoblasts.[10] Immunocytochemical studies with CD34, bcl-2, 21, 24 assists in differentiating lipomas from other myxoid lesions.[18] However, immunohistochemistry was not done in our patient due to financial constraints and the histopathological diagnosis was definite and in accordance with clinical findings.

Approximately, 5–8% of lipoma patients may present with multiple tumors which occur predominantly in upper half of the body and are three times more common in men than in women. The term lipomatosis has been used to describe this condition.[17] In our patient, there was no history or presence of multiple swellings. The occurrence of multiple lipomas can be seen in association with Cowden's syndrome or multiple hamartoma syndrome, Frohlich syndrome, Proteus syndrome, and Bannayan–Zonana syndrome.[217] Most common mucocutaneous lesions in the patients with Cowden's syndrome are small papular lesions in palate and gingiva, papillomatous and verrucous lesions of buccal mucosa, fissured tongue, and multiple cutaneous lipomas.[2] Frohlich syndrome also known as prune belly syndrome is defined by multiple lipomas, obesity, and sexual infantilism.[17] Proteus syndrome is marked by multiple lipomatous lesions, including pelvic lipomatosis, fibroplasia of feet and hands, skeletal hypertrophy, exostoses and scoliosis, and various pigmented lesions of skin.[17] A case of congenital lipoma was described in a 7-year-old boy in upper labial frenum.[3] Bannayan–Zonana syndrome is characterized by congenital association of multiple lipomas, hemangiomas, and macrocephaly.[17]

The main treatment modality for intraoral lipomas and its histologic variants is simple surgical excision.[16] Recurrence rate described after excision is low, but infiltrative lipoma tends to recur after inadequate excision due to the fact that they are not encapsulated like simple lipomas.[2] Steroid injections are used when size of tumor is < 1 inch in diameter and their usage results in local fat atrophy and hence shrinks the size of tumor.[4] Malignant transformation is rare and has been reported, especially for intramuscular lipomas. Malignant tumors are characterized by areas of lipoblastic proliferation, myxoid differentiation, cellular pleomorphism, increased vascularity, and mitosis.[10] Thus, lipomas should be excised completely as there is a rare possibility of malignant transformation.

CONCLUSION

Intraoral lipomas are uncommon tumors which may arise in any site in oral mucosa. However, the occurrence of lipoma on mucogingival junction is rare entity. Patients usually do not seek treatment for oral lipoma as it is mostly asymptomatic and may be observed during routine oral examination. Although the features of lipoma are simple and straightforward, accurate clinical and surgical information along with a histopathological examination is the mainstay to its definitive diagnosis. The possibility of multiple lipomas must be considered and an accurate upper body examination must be done in patients with intraoral lipomas. Clinicians should be aware about the possibility of lipomas in the oral cavity and should always consider it in their differential diagnosis of an inoffensive swelling in oral cavity.

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Conflicts of interest

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