Osteolipoma: a rare tumor in the oral cavity
Sheyla Viana Omonte, DDS,aBruno Augusto Benevenuto de Andrade, DDS, MS, PhD,b Rosana Maria Leal, DDS, MS,cHermínia Marques Capistrano, DDS, MS, PhD,c
Paulo Eduardo Alencar Souza, DDS, MS, PhD,cand Martinho Campolina Rebello Horta, DDS, MS, PhDc
Osteolipoma is a rarely reported histologic variant of lipoma that exhibits bone formation. To the best of our knowledge, only 13 well-documented case reports of osteolipoma in the oral cavity have been published in the English literature. This study presents the clinical, radiographic, and histologic features of an osteolipoma in the oral cavity and reviews the pertinent literature. The patient was a 29-year-old female, who presented with an 8-month history of a painless, progressively enlarging, well-defined, movable submucosal mass in the left posterior buccal mucosa. The lesion had a hard consistency. Imaging findings revealed a spherical radiopacity with an irregular trabecular pattern. The lesion was excised and the diagnosis of osteolipoma was established. No recurrence was observed after a 5-year follow-up. (Oral Surg Oral Med Oral Pathol Oral Radiol 2016;122:e8-e13)
Lipomas are benign mesenchymal neoplasms of soft tissue, which may affect the oral cavity. Previous studies have suggested that 20% of cases occur in the head and neck region, with only 1% to 4% occurring in the oral cavity.1-3 Oral lipomas primarily affect the buccal mucosa,floor of the mouth, and lips.2,3 Histo- logic variants of lipoma are described on the basis of the predominant type of lesional tissue, including fibrolipoma, angiolipoma, myolipoma, leiomyolipoma, myxolipoma, spindle cell lipoma, osteolipoma, chon- drolipoma, and sialolipoma.2,3 Osteolipoma, a lipoma exhibiting bone formation, is a rarer histologic variant among oral lipomas, accounting for less than 1% of cases described in the literature.4-6 Osteolipomas are classified as intraosseous when located in bone and as parosteal or periosteal when located adjacent to bone.
Lipomas that exhibit bone formation but are indepen- dent of bone tissue (nonattached osteolipomas) have been reported in very few cases.5
To the best of our knowledge, only 13 well- documented case reports of osteolipoma in the oral
cavity have been published in the English language literature. Due to its rarity, knowledge about this tumor is incomplete. We describe a case of osteolipoma affecting the buccal mucosa.
CASE REPORT
A 29-year-old female patient presented to the Oral Pathology Clinic at Pontifícia Universidade Católica de Minas Gerais with a painless mass in the left buccal mucosa with an 8- month evolution. The patient had no history of trauma in that region. The medical history and systemic review were noncontributory. Physical intraoral examination showed a 1.5 1.5 cm, well-defined, movable submucosal mass in the left posterior buccal mucosa, near the retromolar triangle (Figure 1A). The lesion had a yellowish appearance and hard consistency. The overlying mucosa showed telangiectasia but no ulceration or erythema (Figure 1B).
Because the mass presented a hard consistency, a radio- graphic examination was performed. Imaging findings revealed a round area of radiopacity, with an irregular pattern of trabeculae, and no evidence of cortical abnor- mality or influence on the surrounding structures was found (Figure 2).
The clinical differential diagnosis included oral osseous choristoma (soft tissue osteoma), cartilaginous choristoma, osteolipoma, chrondrolipoma, pleomorphic adenoma with ossification, and other salivary gland or connective tissue tu- mors with dystrophic calcification. It was free from the peri- osteum and not attached to any adjacent structures, such as the mandibular bone. With the patient under local anesthesia, the lesion was completely excised. It was free from the perios- teum and not attached to any adjacent structures, such as the mandibular bone. The surgical specimen was sent to the Oral Pathology Laboratory.
Grossly, the resected specimen consisted of a mass measuring 1.8 1.5 1.2 cm, which was well circumscribed and yellowish with soft and focal hard consistency (Figure 3A). On sectioning, the mass exhibited a yellow soft tissue with various intermixed thin lamellar bony structures and afibrous capsule (Figures 3B and 3C).
Microscopically, the mass presented abundant mature adi- pose tissue, with no atypia, and was separated by thinfibrous The case reported in this manuscript was previously presented in the
III Brazilian Digital Oral Pathology Meeting, September 2013.
Financial support was provided by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes), Brazil; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil; Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG), Brazil.
aGraduate Student, Graduate Program in Dentistry, School of Dentistry, Pontifícia Universidade Católica de Minas Gerais, Belo Horizonte, Brazil.
bOral Pathology Division, Department of Oral Diagnosis and Pa- thology, School of Dentistry, Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, RJ, Brazil.
cOral Pathology Division, School of Dentistry, Pontifícia Uni- versidade Católica de Minas Gerais, Belo Horizonte, Brazil.
Received for publication Jul 30, 2015; returned for revision Sep 1, 2015; accepted for publication Sep 17, 2015.
Ó 2016 Elsevier Inc. All rights reserved.
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Vol. 122 No. 1 July 2016
connective tissue septa. Randomly distributed irregular trabeculae of immature bone, with osteoblastic activity, were found throughout the tumor. No foci of hematopoietic cells were observed (Figures 4A-D). The lesion was surrounded by a thin osseous layer and a fibrous capsule (seeFigure 4A).
The surgical margins were tumor-free.
Afinal diagnosis of osteolipoma was established. The re- covery course was uneventful, and no recurrence was detected after a 5-year long follow-up.
DISCUSSION
Lipomas are common benign soft tissue tumors,7,8 appearing most commonly in areas of the body where adipose tissue is present.9 The subcutaneous or submucosal region is the usual site, but these can develop between skeletal muscle fibers, on bone surfaces, or within deep soft tissues.7 The tumor may undergo a variety of changes. An uncommon change is ossification.1,5,6,8-17 To our knowledge, only 13 cases of oral osteolipomas have been reported in the English language literature. Table I summarizes their features.
Although oral lipomas are believed to be more common in men,3no clear gender preponderance has been observed in patients with osteolipomas of the oral cavity (see Table I), except for one case of a young boy with an osteolipoma in the palate, most patients affected by oral osteolipoma were adults.
Most cases were reported in patients over 40 years of Fig. 1. Clinical aspects of oral osteolipoma.A, Well-defined,
movable submucosal mass showing yellowish appearance, hard consistency and a size of 1.5 1.5 cm located in the left posterior buccal mucosa, near the retromolar triangle.B, The overlying mucosa showed telangiectasia without ulceration or erythema.
Fig. 2. Radiographic aspects of oral osteolipoma. Radiog- raphy revealed a spherical radiopacity with an irregular pattern of trabeculae, and no evidence of cortical abnormality or influence on the surrounding structures was found.
Fig. 3. Gross appearance of oral osteolipoma.A, The resected specimen consisted of a mass measuring 1.8 1.5 1.2 cm that was well circumscribed and yellowish, with soft and focal hard consistency.B and C, On sectioning, the mass revealed a yellow soft tissue with various mingled thin lamellar bony structures and afibrous capsule.
age. A long history of slow progression is commonly observed, although our patient had the lesion for only 8 months.
As evident inTable I, osteolipomas of the oral cavity can occur in various anatomic sites, regardless of the proximity to bone. Four cases occurred in the buccal mucosa, four in the mandibular buccal mucosa (vestibule or alveolar mucosa), three in the hard palate, two in the floor of the mouth, and one in the lateral tongue. In the cases of tongue osteolipoma, osteocartilaginous choristoma, osteosarcoma, liposarcoma with metaplasia, and post-traumatic chondrification had been considered in the differential diagnosis.9 In one case involving the alveolar mucosa, exostosis, peripheral giant cell granuloma, fibrous hyperplasia, and fibroma with calcifications had been considered5; and in a case of a palatal osteolipoma, the differential diagnosis had included osteoma, neurofibroma, and intraosseous palatal cyst.6Additionally, with regard to the differential diagnosis, in osteolipomas exhibiting radiographic features, such as the present case, the clinician should consider oral osseous choristoma (soft tissue osteoma), cartilaginous choristoma, chrondrolipoma, pleomorphic adenoma with ossification, and other salivary gland or connective tissue tumors with dystrophic calcification.
Suggestive clinical and radiographic features (hard or soft peripheral mass generally associated with a radi- opaque area), as well as the histopathologic appearance of mature fatty tissue with diffuse bone trabeculae, usually confirm the diagnosis of osteolipoma (Table I).
However, these features are also found in oral osseous choristoma. The term oral osseous choristoma was coined by Krolls et al.18 in 1971 to describe benign bone formations in oral soft tissue, previously referred to as soft tissue osteomas. Although oral osseous choristoma generally exhibit a mass of dense lamellar bone,19 which is easily differentiated from an osteolipoma, some of these lesions can display a cancellous pattern. These osseous choristomas, such as the case described by Hodder and MacDonald20 in 1988, display spongy bone trabeculae containing abundant bone marrow spaces filled with fatty tissue, a histologic organization suggestive of that found in osteolipoma. Generally, foci of hemopoietic marrow are encountered in osseous choristomas20 but not in osteolipomas.4 Hence, this characteristic may be important in the differential diagnosis. Both lesions are benign connective tissue lesions, which are treated by conservative surgical excision and exhibit similar prognoses.
Fig. 4. Histopathologic features of oral osteolipoma. Abundant mature adipose tissue with no atypia and separated by thinfibrous connective septa was observed. Randomly distributed irregular trabeculae of immature bone exhibiting osteoblastic activity were found throughout the tumor. The tumor was surrounded by a thin osseous layer andfibrous capsule. No foci of hematopoietic cells were observed (A, H&E, 20; B, H&E, 40; C, H&E, 100; D, H&E, 200). A high-resolution version of this slide for use with the Virtual Microscope is available as eSlide: VM01035.
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Author (Years) Gender Site Clinical presentation Imagingfindings Duration Histopathology
Godby et al.11 54 Male Floor of the mouth Painless and soft mass. Size:
7.0 6.0 3.0 cm (gross examination)
Radiopaque mass (occlusal radiography)
1 year Mature adipose tissue, well-formed cancellous bone,fibrous connective tissue and striated muscle
Hughes CL12 69 Male Mandibular buccal
vestibule
Painless and soft yellowish
“walnut-size” mass Slight facial asymmetry
No evidence of alterations (radiography)
NA Fat cells with foci of ossification
surrounded byfibrous connective tissue
Allard et al.13 81 Female Mandibular buccal
vestibule
Facial asymmetry
Painless and hard“walnut-size”
mass
Well defined radiopaque mass with a pattern of irregular trabeculae (occlusal radiography)
30-40 years Homogeneous adipose tissue containing fibrous septa and irregular trabeculae of lamellar bone without hematopoietic tissue
Piattelli et al.9 49 Female Lateral margin of
the tongue
Painless and hard mass Size: 0.8 cm in diameter
NA 8 years Mature adipose tissue containing lamellar
bone surrounded by afibrous pseudocapsule
Castilho et al.8 65 Female Buccal mucosa Painless and soft yellowish mass
Size: 1.0 1.0 0.8 cm (gross examination)
NA NA Mature fat cells supported byfibrous
septa.
Focal areas of woven bone surrounded by fusiform-shaped mesenchymal cells
Saghafi et al.5 68 Male Mandibular buccal
alveolar mucosa
Painless and hard mass. Size:
1.5 1.0 cm No evidence of cortical
abnormality or influence on the surrounding structures (radiography)
4 years Adipose tissue with foci of lamellar bone surrounded by mesenchymal cells
Gokul et al.14 6 Male Hard palate
(associated with cleft of hard and soft palate)
Painless and soft mass. Size:
3.0 2.0 cm
Well-defined hypodense lesion arising with mixed density, showing a well-defined radiodense body (computed tomography)
Congenital Lobules of adipose tissue separated by fibrovascular connective tissue septa and showing the presence of mature bone
de Castro et al.1 47 Female Buccal mucosa Facial asymmetry
Painless nodule. Size: 1.5 cm in diameter
An irregular and radiopaque structure (radiography of the surgical specimen)
1 year Trabeculae of lamellar bone inside a mature adipose tissue surrounded by thin septa of conjunctive tissue
Adebiyi et al.6 37 Female Hard palate Painless and hard mass. Size:
3.0 4.0 cm
Patchy areas of radiopacity (occlusal radiography)
10 years Mature adipose tissue with scattered trabeculae of lamellar bone
Hsu et al.15 71 Male Buccal mucosa Painless and hard mass. Size:
4.0 2.5 cm
NA 4 years Lobules of mature adipose tissue
separated byfibrous septa Randomly distributed trabeculae of
mature lamellar bone and foci of woven bone
Bajpai et al.16 55 Male Hard palate Painless and hard yellowish mass
Size: 1.5 1.4 cm Patchy area of radiopacity
(occlusal radiography)
4 years Bone trabeculae surrounded by lobules of mature adipocytes separated byfibrous septa
(continued on next page)
CASEREPORT
122,Number1Omonteetal.e11
The pathogenesis of osteolipomas has not yet been clarified. Some authors have suggested that osteolipo- mas may originate from two types of undifferentiated mesenchymal cells that separately form adipose and bone cells.21 An alternate theory proposes that multipotent adipose-derived stem cells within adipose tissue may be involved in osteolipoma development.
Thus, bone tissue develops inside a lipoma in response to growth signals.22 This theory hinges on the assumption that adipose-derived stem cells have the potential to differentiate into fat, bone, cartilage, and vascular components.23 Some other authors have suggested that repetitive trauma, metabolic changes, or ischemia may lead to metaplasia of pre-existing fibrous elements within lipomas, which then develop into osteoblasts.24,25 The conditions that induce the differentiation of mesenchymal stem cells into bone remain to be investigated.
CONCLUSIONS
Although osteolipoma is a very rare entity in the oral cavity, it should be considered when a patient presents with a peripheral lesion that has a hard consistency on palpation, areas of radiopacity in image examinations of peripheral lesions, and mature adipose tissue associated with bone trabeculae in histopathology. It has the same prognosis as a simple lipoma, and surgical excision is the recommended treatment. Recurrences have not been reported.
The authors wish to thank the Oral Diagnosis Department, Piracicaba Dental School, University of Campinas, Brazil, for technical assistance with high-resolution slide scanning.
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TableI.Continued AuthorAge (Years)GenderSiteClinicalpresentationImagingfindingsDurationHistopathology Amaraletal.10 51MaleMandibularbuccal mucosaSlightfacialasymmetry.Painless andhardmass.Size:2.01.5 cm Well-definedhyperechogenic masswithareasofcalcification (ultrasonography) 3yearsProliferationofmaturefatcellswith centralareasoflamellarbone trabeculaeandfibroussepta Raghunathand Manjunatha1720FemaleFloorofthemouthPainlessandhardyellowishmass Size:6.06.0cmWell-defined,hypodenselesion withirregularhyperdenseareas (computedtomography)
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8monthsMatureadiposetissuewithfibroussepta andirregulartrabeculaeofimmature bone Tumorsurroundedbyathinosseouslayer andafibrouscapsule NA,notavailable.
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500, Prédio 46 Sala 101
Coração Eucarístico
Belo Horizonte e Minas Gerais Brazil
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