Ⅰ. INTRODUCTION

Lipomas are the most common benign mesenchymal tumors composed of mature adipocytes.(1) They are usually slowgrowing, soft and asymptomatic masses. Enzinger and Weiss classified benign lipomatous tumors into 5 groups: 1) lipoma; 2) varients of lipoma; 3) heterotopic lipomas, neoplasms, or hamartomatous lesions; 4) infiltrating or diffuse neoplastic or nonneoplastic proliferations of mature fat; and 5) hibernoma.(2) Lipoma of the oral cavity is a common benign soft tumor. However, angiolipoma, showing characteristics of both lipoma and hemangioma, usually develop in the trunk and extremities, and rarely arise in the head and neck region.(3) Angiolipoma of the cheek is very rare.

Angiolipomas are rare benign soft tissue tumors that are distinguished from common lipomas by a marked degree of vascularization.(1) The diagnosis and prognosis of angiolipomas are based entirely on the findings of histological evaluations.(4)

This report presents the clinical and histopathological features of infiltrating angiolipoma excised from the cheek.

Ⅱ. CASE REPORT

A 32-year-old man with an apparently good general health visited the oral and maxillofacial surgery department at the Seoul St. Mary's hospital of Catholic University of Korea, with swelling on the lower right side of the face since 2 weeks. It was not associated with pain, paresthesia or discharge. On extraoral examination, approximately 3×3×2cm swelling extending from corner of mouth to 3cm anterior to ear was present on right cheek(Fig. 1). The overlying skin was normal. Swelling was well circumscribed, soft in consistency, movable, tender, non-fluctuant and no bruit was present. On intraoral examination a non-fluctuant swelling of approximately 2×2 cm was noted(Fig. 2). Based on the clinical findings, hemangioma, was given as provisional diagnosis.

Magnetic resonance imaging(MRI) showed an oval heterogeneous mass in the cheek with a mixed pattern of high and low intensity on T1-weighted spin echo(Fig. 3). The mass extended through the masticatory space, forming well-defined multinodules on T2-weighted spin echo(Fig. 4). The entire mass measured 5.0×2.9cm.

Surgical excision was performed under general anesthesia through an intraoral approach. First we tried aspiration to find out the exact spot of the lesion and reduce the volume(Fig. 5). Since it was not adhering to the surrounding tissue, detachment was easy and the mass was removed as a lump and sent for histopathological examination(Fig. 6).

Macroscopic examination revealed, a single bit of tissue which was 5.5×3.2×1.8 cm in size, irregular in shape, dark brown in color, soft in consistency having irregular borders(Fig. 7).

Microscopic examination of a biopsy specimen showed diffuse and infiltrative growth of fatty tissue into surrounding fibrovascular tissue. There also appeared severe vascular proliferation, resulted in hamartomatous proliferation resembling cavernous hemangioma and the tumor was nonencapsulated (Fig. 8). A clinical diagnosis of angiolipoma was made on the basis of findings obtained by MRI, and biopsy.

Our patient reported 2 weeks postoperatively without any discomforts and no signs of recurrence(Fig. 9, 10).

Ⅲ. DISCUSSION

Angiolipoma was first described as a rare entity in 1912 by Bowen(5), but was established as a distinct entity in 1960 by Howard and Helwig.(6) Angiolipoma is characterized histologically by a mixture of mature adipocytes and interspersed vascular structures with fibrin thrombi.(7) Later it was classified as infiltrating and non-infiltrating types depending on the histopathological features.(8)

Infiltrating angiolipomas are characterised by a non-encapsulated tumour and extend into surrounding tissues. They have two anatomical forms: intermuscular and intramuscular.(5) Infiltrating angiolipomas represent less than 10% of angiolipomas, and they are characteristically unencapsulated or partially encapsulated.(9)

Angiolipoma generally occurs in teenagers and young adults as a subcutaneous, tender to painful, single or, more commonly, multiple nodules involving the trunk or extremities.(10) This tumor is most common in young adults and is located in the upper extremity in nearly two-thirds of cases.(11) It is rare for this tumor to occur in the head and neck region. Angiolipoma occurs very rarely in the mandible.

There is no general agreement about the cause of the pain.(12) The aetiology of lipoma is still unknown. However, in the literature, trauma is also mentioned as one of the aetiological factors.(13) The first is that, after trauma, adipose tissue prolapses through fascia, resulting in a direct impaction. The second opinion is that, after soft tissue trauma and haematoma formation, cytokines mediate differentiation and proliferation of preadipocytes, resulting in lipoma formation.(14) Differentiation and progression to vascular proliferation may be triggered by later stimuli, such as repeated mild trauma.(15) There may be an increased incidence of angiolipomas in homosexual men.(16)

In contrast to the usual location, its diagnosis in maxillofacial region often requires special procedures.(17) Typically, the diagnosis is made only after excision of the mass and microscopic examination.(18) The tissue diagnosis in infiltrating angiolipoma is usually without difficulty. A nonencapsulated (rarely partially encapsulated) tumor composed of mature lipocytes with delicate, proliferating blood vessels wedging haphazardly into the surrounding tissue is the classic picture of infiltrating angiolipoma.(9)

Mascalchi et al reported that infiltrating angiolipoma should be diagnosed on MRI when an extending mass associated with a progressive clinical course shows isointensity or hyperintensity on T1-weighted images and hyperintensity on T2-weighted images and displays contrast enhancement.(19) Because the adipose tissue was intensified on T1WSE, and characteristics of a blood-pooling angioma were seen on T2 WSE, the vascularity seemed to differ in the upper and lower parts of the tumor in the current case.(3) T1-weighted spin echo and hyperintensity on T2-weighted spin echo and displays contrast enhancement.(19)

The radiographic findings of angiolipoma are fairly distinctive. CT shows a homogenous lesion; however, the addition of contrast demonstrates a central low-density mass surrounded by areas of contrast enhancement representing the vascular component, a feature uncommon in a more typical lipoma. MRI is considered the best and most sensitive imaging modality for angiolipoma, typically revealing homogenous low-intensity areas without contrast enhancement and heterogeneous areas of extremely high contrast enhancement corresponding to the dense vascularity. However, angiolipoma does not generally demonstrate aggressive soft tissue infiltration or bony destruction.(20)

In the present case, we performed surgical excision. These lesions have been removed by both intraoral and external approaches depending on the relation of lesion to oral cavity. The intraoral approach has better cosmetic result.(21) In contrast, wide resection is recommended for the management of infiltrating angiolipomas, mainly because of the risk of recurrence.(9) Treatment of infiltrating angiolipomas is completely excision with close follow-up. Infiltrating angiolipomas have not been found to undergo malignant transformation, but the recurrence rate of all infiltrating angiolipomas is 35–50%.(9,22) No recurrence of infiltrating angiolipomas in the head and neck have been reported.(16)

Data analysis showed that there was no gender predominance(1.2:1).(23) However, the recurrence rate for infiltrating angiolipoma is 35% to 50%,(9,24) and therefore wide surgical excision with adequate margins of healthy tissue is recommended for the management of the tumor.(9)

The infiltrating type can create some difficulty in excision, and the recurrence rate is high.(25) Some believe it could represent diffuse angiomatosis associated with fat rather than a neoplasm.(26)

Infiltrating angiolipoma differs from noninfiltrating angiolipoma by its ability to infiltrate surrounding structures, such as the muscle, joint tendon, bone, fibrocartilage, and neural tissue.(9) Infiltrating angiolipoma should be differentiated from infiltrating(intramuscular) lipoma, Kaposi sarcoma, and intramuscular hemangioma.(23) The presence of fibrin thrombi in vascular channels differentiates infiltrating angiolipoma from infiltrating hemangioma with a significant admixture of fat.(27)