Lipomas are the most common soft tissue mesenchymal neoplasms identified in adults. They are characterized by the proliferation of mature white adipocytes without cytologic atypia and usually present as well-circumscribed, painless, rubbery, solitary nodules. Lipomas are relatively common in the extremities and are rarely observed in the head and neck region; they reportedly account for 15%-20% of all benign tumors^1-8. Soft-tissue lipomas can be categorized into two subtypes: those arising in subcutaneous tissues and those that are localized deep in muscle; the former are more common, while the latter, known as intramuscular or infiltrating lipomas, are much more rare, accounting for less than 1% of all lipomas.

In this case, treatment involves curettage of the lesion without grafting the cavity. A literature search of PubMed yielded few case reports of lipomas involving the masticatory space. This paper presents a case of surgical resection of a lipoma that occurred extensively on the medial aspect of the mandibular ramus and condylar head and neck while performing orthognathic surgery.

An 18-year-old female patient was referred to our hospital in March 2023 for orthognathic surgery for the management of facial asymmetry and mandibular prognathism. The patient had received orthodontic treatment for orthognathic surgery at a private clinic 1 year prior. Her medical and dental histories were unremarkable. Clinical and radiological examinations were conducted prior to performing orthognathic surgery.(Fig. 1)

Extraoral and intraoral examinations did not reveal any abnormalities. No signs of cortical expansion or mucosal anomalies were observed. The patient was asymptomatic and did not present with facial swelling, pain, or temporomandibular dysfunction.

Radiography revealed a radiolucent lesion on the right mandibular ramus. No history of temporomandibular joint injury or pathology was reported. The panoramic radiograph and cone-beam computed tomography (CBCT) revealed a radiolucent, well-circumscribed lesion in the right mandibular ramus and a condylar deformity.(Fig. 2) CBCT also revealed a cortical bone defect in the medial aspect of the ascending ramus.(Fig. 3) The lesion was located posterior to the inferior alveolar nerve channel, and thinning of the cortical bone was observed in the mandibular ramus. Magnetic resonance imaging (MRI) revealed a hyperintensive lesion typical of fat in the T1- and T2-weighted sequences.(Fig. 4) CT revealed a lipomatous mass with bone deformity and thinning in the right condyle of the mandible. All of these features were consistent with the diagnosis of a lipoma.

The patient presented with an angle class III maxillomandibular relation with facial asymmetry. The treatment plan was resection of the lipoma along with orthognathic surgery, including a Le Fort I osteotomy and bilateral sagittal split ramus osteotomy (BSSRO). The plan was to move the maxilla forward, conduct differential posterior impaction, and move the mandible backwards to correct the maxillomandibular relation.

First, the maxilla was fixed with plates and screws after Le Fort I osteotomy. Next, on the mandible, an incision along the anterior border of the ramus and external oblique ridge was executed to enable completion of the BSSRO procedure. On the right side, the lipoma was resected by sagittal split osteotomy. An approach was made between the separated segments, and then excisional biopsy was performed. In our case, bone grafting or filling was considered unnecessary. After the final bite occlusion was checked, all incisions were sutured properly at the end of the operation.

During surgery, well-defined resorption of the external cortex of the right mandibular ramus was observed, as anticipated, on the radiographic image. The lesion appeared as fatty tissue. Resection through curettage was performed, and filling of the defect was considered unnecessary.(Fig. 5) Pathological findings confirmed the definitive diagnosis of a lipoma.(Fig. 6) Clinical and radiographic examinations during the 6-month follow-up period after surgery confirmed satisfactory bony union. Furthermore, the patient showed good healing, without any deformation or temporomandibular disorder, and recurrence has not been observed to date.

Lipomas are common benign tumors of the adipose tissues that can manifest in various regions of the body, with a predilection for the trunk and proximal extremities. Typically appearing as solitary, soft, well-circumscribed, slow-growing masses, lipomas may be subcutaneous and often asymptomatic, or deep, potentially causing pressure-related symptoms. They are commonly observed in individuals aged 40-60 years and show no sex or racial predilection^9,10. Although subcutaneous lipomas predominantly affect the upper back, neck, shoulders, and abdomen, they occasionally occur on the face.

Even though many authors consider lipomas to be true benign neoplasms, the origin of intramuscular lipomas remains elusive. These tumors appear in a wide range of age groups; however, the average age reported in most cases has been approximately 48 years. Nearly 25% of patients with lipomas present with no symptoms, and the lesion is often discovered incidentally. Surgical intervention, either curettage or local resection, is the recommended choice of treatment in these patients. Recurrence of intramuscular lipomas is rare, with only two documented cases. Additionally, four cases have reported the malignant transformation of intraosseous lipomas. Interestingly, there are no reports of recurrence or malignant changes in mandibular intraosseous lipomas^1-5.

Lipomas are rarely observed in the bones in the head and neck region. Furthermore, it is rarely reported that lipomas affect bone. Sixteen cases (in seven males and nine females) of lipoma involving the jaw have been reported since 1948, most of which were diagnosed as odontogenic cysts based on the radiographic images. Making a differential diagnosis is essential when encountering other radiolucent bone images, which include a simple cyst, post-traumatic cyst, aneurysmal bone cyst, giant-cell granuloma, ameloblastoma, osteoblastoma, arteriovenous malformation, hemangiomas, infarcted bone, chondrosarcoma, and liposarcoma⁶.

Radiography revealed a radiolucent lesion in the right mandibular ramus. The patient had no history of temporomandibular joint disease or pathology. Orthopantomography revealed a well-defined radiolucent lesion in the right mandibular ramus with evidence of a condylar deformity. A cortical bone defect was observed in the medial aspect of the ascending ramus on the CBCT scan. The lesion was positioned behind the alveolar nerve channel, and thinning of the cortical bone in the mandibular ramus was apparent. On MRI, the lesion appeared hyperintense in both the T1- and T2-weighted sequences, which is a characteristic feature of adipose tissues¹¹. Medical CT indicated the presence of a lipomatous mass, along with bone deformities and thinning of the right mandibular condyle. These findings were consistent with a diagnosis of lipoma¹².

The treatment plan was resection of the lipoma along with orthognathic surgery, including a Le Fort I osteotomy for the maxilla and bilateral sagittal split osteotomy for the mandible. There is a high risk of surgical complications, such as unfavorable splitting or pathologic fracture in the affected ramus, during orthognathic surgery in patients with mandibular bone defects due to a lipoma. Nevertheless, it is easy to access the lipoma in such cases because the ramus is split during BSSRO, and no aesthetic scarring is incurred when approached intraorally. Under general anesthesia and during orthognathic surgery, an excisional biopsy was performed.

Resorption of the external cortex in the right mandibular ramus was observed during the entire surgical procedure, which aligned with the expectations derived from the radiographic image. The lesion exhibited characteristic radiographic features consistent with those of fatty tissue. Curettage was performed, and filling the defect was deemed unnecessary. The pathological findings conclusively confirmed the diagnosis of lipoma. Six months after her surgery, the patient was symptom-free, with no signs of relapse.

In previous studies, although they are limited in number, it has been reported that lipomas that occurred inside the mandibular ramus and condylar head and neck were removed by an extraoral approach^2,13. Any lesion in this area will almost certainly require this approach. However, we introduce a case here in which an intramuscular lipoma of the right mandibular ramus and condylar head and neck was removed by an intraoral approach through orthognathic surgery^5,6,13. During the 6-month follow-up period after surgery, bony union was satisfactory, and unfavorable splitting was not observed. During clinical and radiographic examinations, the patient showed no deformation or dysfunction, and recurrence has not been observed.(Fig. 7) Moreover no evidence of any change in bone formation was observed by 6-month postoperative CBCT.(Fig. 8) In conclusion, even though they are very rare, intramuscular lipomas can arise in the head and neck region. As in this case, there is a high risk of surgical complications during orthognathic surgery in patients with mandibular bone defects due to lipoma. Nevertheless, accessing the lipoma in this context is easy because the ramus is split during BSSRO, and no aesthetic scarring occurs when approached intraorally; as such, resection of the lipoma and orthognathic surgery were performed together. Follow-up at 6 months postoperatively showed good healing without any deformation or dysfunction, and recurrence has not been observed so far; nonetheless, long-term follow-up is required.