Mandibular intraosseous lipoma: clinical features of a condylar location

Abstract

Lipomas are common benign neoplasms affecting many adipose tissue-containing organs of the body, including bone. Central lesions in bone account for less than 1% of all lipomas. In the literature, intraosseous lipomas have been reported in various bones such as the frontal and parietal bones, ribs, ulna, phalanges of hand and foot, femoral neck, fibula and calcaneum. No preference has been described for gender or race. As far as the authors know, there have been no documented cases of intraosseous lipoma involving the temporomandibular joint. This report describes a rare case of mandibular intraosseous lipoma in the left condylar area associated with temporomandibular dysfunction.

According to the World Health Organization definition, a lipoma is a tumour of mature adipose tissue with no evidence of cellular atypia. Lipomas are one of the most common forms of benign tumour of the soft tissue. They are predominantly located subcutaneously, but can also be found in intramuscular, retroperitoneal, interosseous and intraosseous locations. The incidence of intraosseous lipoma based on literature reports represents less than 0.1% of all bone tumours. Intraosseous lipoma is rarely seen in head and neck bones. The cranio-facial involvement of an intraosseous lipoma may be misdiagnosed. The authors report the case of a mandibular intraosseous lipoma with a rare condylar location, and discuss its nature, diagnosis and treatment .

Case report

A 61-year-old woman was referred for evaluation of a soft swelling located in the left mandibular ramus and preauricular region, which had appeared 2 years previously. The main symptoms were severe pain in the affected areas and impaired mouth opening that led to the diagnosis of temporomandibular dysfunction syndrome. The patient’s medical history relating to the condition showed no response to conservative treatment with medication, physiotherapy and occlusal splint. She had no other relevant medical history, no previous history of facial trauma, no history of cancer in her family and was an occasional smoker and a social drinker. On examination, mandibular movement was severely limited with a maximum jaw opening of 20 mm. The patient had not experienced hearing loss during the preceding months. Facial nerve function was intact and there was no evidence of palpable cervical lymphadenopathy. The rest of the head and neck examination was normal.

A 2-cm long oval-shaped radiolucent lesion with light peripheral enhancement was present in the left mandibular condyle occupying almost its entire thickness in control panoramic radiographs ( Fig. 1 ). Computed tomography revealed a unilocular, well-defined radiolucent image located in the left condylar area with no evidence of cervical lymphadenopathy ( Fig. 2 A and B ). Magnetic resonance imaging (MRI) showed enhancement of a unilocular lesion in the mandibular condyle. This focal condylar lesion had an ovoid morphology that was well defined and markedly dense, that adapted to the major axis of the left ascending ramus of the mandible. The T1-weighted MRI image was also intense on the gradient echo sequence. These MRI features are consistent with adipose tissue ( Fig. 2 C). No fine-needle aspiration or incisional biopsy was performed.

Fig. 1
Well-defined radiolucency in the left mandibular condyle (panoramic radiography).

Fig. 2
(A and B) CT showing two different images of the osteolytic condylar lesion. (C) MRI demonstrating an enhancement of a unilocular lesion in the mandibular condyle. This focal condylar lesion presents with a well-defined and markedly dense ovoid morphology that adapts to the major axis of the left ascending ramus of the mandible.

With the patient under general anaesthesia, an arthrotomy was performed via an endaural incision to gain access to the temporomandibular joint. After removing the cortical bone, local resection of the condylar lesion was carried out ( Fig. 3 ). The clinical and radiological diagnosis was confirmed by surgical observations. The tumour appeared without any obvious infiltration into the surrounding tissues and was subsequently completely excised. The wound was drained and closed in layers. The patient was discharged on the third postoperative day to be followed up at the outpatient clinic. A soft food diet was advised for the first month and normal sustenance thereafter.

Fig. 3
Intraoperative articular aspect (condylar and glenoid fossa). An arthrotomy was performed via an endaural incision to gain access to the temporomandibular joint. Clinical and radiologic diagnosis was confirmed by surgical observations.

In this case, a diagnosis could not be made preoperatively. The tumour in the central cavity of the condylar area was whitish in colour and with a soft-elastic consistency. The margins of the surgically resected tissue appeared without tumour and there was no osseous infiltration. These features exclude the possibility of metastatic tumour. The tissue was examined by pathologists and the histological diagnosis was of a mandibular intraosseous lipoma ( Fig. 4 A and B ).

Fig. 4
(A) The large tumour specimen in the central condylar cavitation had a whitish colour and a soft-elastic consistency. The margins of the surgical resection appeared to be tumour free. Histological diagnosis indicated a mandibular intraosseous lipoma. (B) Higher magnification of A.

After 6 months, the patient had normal masticatory function with improved mouth opening and no pain. 1 year postoperatively the patient was pain free and had a jaw opening of 45 mm. The temporomandibular dysfunction syndrome was completely resolved. Clinical examination and imaging studies showed excellent long-term stability of the temporomandibular joint.

Discussion

Lipoma is a common, benign tumour of adipose tissue that may affect any part of the body, although the trunk and proximal extremities are the most likely sites. It usually presents as a solitary, soft, well-circumscribed, mobile, slow-growing mass. Lipomas may be subcutaneous, where they are typically asymptomatic, or deep, in which case they may cause pressure-related symptoms as in the present case. They occur more commonly in those aged 40–60 years and have no gender or race predilection. Subcutaneous lipomas often affect the upper back, neck, shoulder and abdomen, but may infrequently arise on the face. Despite the large amount of fatty marrow in adults, intraosseous lipomas are unusual and are regarded as one of the rarest primary benign tumours of bone .

The aetiology of intraosseous lipoma is unknown, but most authors think it represents a true benign neoplasm. Although the tumour shows a wide age distribution, the average age of the reported cases is approximately 48 years. About 25% of patients with this tumour have no symptoms and the lesion is found incidentally. The recommended treatment is surgical intervention by curettage or local resection. Recurrence of the intraosseous lipoma is rare and has been reported in only two cases. Four cases of malignant transformation of intraosseous lipoma have been reported. No recurrence or any malignant changes of mandibular intraosseous lipomas have been reported .

Lipoma is rarely seen in the head and neck bones. 16 cases (seven males, nine females) of lipoma have been reported to involve the jaw since 1948, most of which were diagnosed as odontogenic cysts based on radiographic images. The cranio-facial involvement of an intraosseous lipoma may be misdiagnosed. To prescribe the correct treatment, it is important to distinguish between cysts and lipomatous tumours. Radiographic images of the jawbones generally show a unilocular or multilocular radiolucent image with a honeycomb or soap bubble appearance, depending on the size of the spaces formed. These lesions vary in size, which contributes to the possibility of misdiagnosis. The absence of clinical signs such as spontaneous bleeding or erythematous surface, associated with the radiographic features tends to rule out an angiomatous lesion .

M ilgram , who reported the largest case series, describes three stages of intraosseous lipomas based on their pathological features. Stage 1, in which there is no secondary necrosis. Stage 2, in which there is partial necrosis. Stage 3, in which there is complete secondary necrosis. The present case is classified as a stage 1 lesion. When composed of a unilocular radiolucent lesion with light peripheral enhancement, as in the present case, the lesions are considered benign. When composed of an osteolytic lesion with irregular borders and the involvement of soft tissue, malignancy should be suspected. MRI is useful for making distinctions of this type, and also allows analysis of fatty tissue inside the marrow cavity, as in the present case. Image interpretation must be accurate, because not all lipomatous lesions can be diagnosed in this manner. Histological variants of lipomatous lesions such as pleomorphic lipoma may not be detectable with MRI. Pleomorphic lipoma and spindle cell lipoma are distinguished as benign lesions that are histologically similar to liposarcoma. The MRI aspects of some intraosseous lesions are not well defined. In the present case, liposarcoma was eliminated because of the lack of nuclear or cellular atypia and infiltrative growth was not observed clinically, radiologically and pathologically .

In the present patient, the lesion appeared in CT as a well-defined, unilocular radiolucent image involving the left subcondylar area. The anterior, posterior and lateral limits were intact, while respecting the contour of the mandibular bone in this area, and there was no involvement of the soft tissue. This evidence is characteristic of a mandibular intraosseous tumour. The MRI did not reveal any communication between the lesion and perilesional soft tissues. Such findings in diagnostic imaging studies are consistent with a benign lesion of slow evolution .

This report describes a mandibular intraosseous lipoma in the condylar area associated with temporomandibular dysfunction. The anatomical location and proximity of this tumour to the temporomandibular joint could have long-term functional implications if proper anatomical relationships are not accurately re-established. The functional outcome of local resection in this case has been satisfactory.

To the best of the authors’ knowledge, this is the first report of an intraosseous lipoma arising in the temporomandibular area. The diagnostic radiological study showed an osteolytic image with peripheral sclerosis, which tended to expand within the bone, occupying almost its entire thickness. Central calcification was not present, making the lesion difficult to distinguish from a simple bone cyst. MRI distinguished the lipoid and cystic nature of its content. Histopathological findings showed a benign tumour composed of mature adipose tissue with no evidence of malignancy.

In conclusion, intraosseous lesions in the mandibular condyle are uncommon and are difficult to diagnose. When considering the surgical risks involved in removal of the lesion, the differential diagnosis between benign and malignant tumours is of great importance. If the patient presents symptoms the treatment should be surgical removal of the lesion. There are few reported cases in the literature of the appearance of intraosseous lipoma in the jaw bones. The exact nature of these lesions is debatable, but it is widely accepted that they represent true benign tumours. The features for and against this lesion being of a neoplastic origin are discussed. The characteristic histopathological findings were the presence of only mature adipose fat cells.

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Feb 8, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Mandibular intraosseous lipoma: clinical features of a condylar location
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