World Health organization (WHO) classification of benign lipomatous tumors recognizes conventional lipoma, fibrolipoma, angiolipoma, spindle cell/pleomorphic lipoma, myxolipoma, chondroid lipoma, osteolipoma, myolipoma, lipomatosis, lipomatosis of nerve, lipoblastoma/lipoblastomatosis, and hibernoma [1]. Lipomas are the most common mesenchymal tumors of soft tissue, but they are relatively uncommon in the oral and maxillofacial region [7], being no more of 4% of the tumours occurring in this sites [8]. Buccal and tongue mucosa are the most frequent sites, followed by the floor of the mouth, buccal vestibule, palate, lips, and gingiva [7]. Although a male predominance has been reported [4], some authors found an equal gender distribution for oral lipomas [3].
Intramuscular (infiltrating) lipoma is a rare variant of lipoma first defined by Regan and his colleagues in 1946 [9]. Clinically, oral intramuscular lipoma presents as a well circumscribed painless, solitary, rubbery, submucosal swelling. Although it arises in the deeper tissues of tongue [6], a protrusion from the lingual mucosa can be documented in most large-sized lesions [10]-[12]. We report an unusual case of a giant lipomatous lesion of the tongue which fulfilled all the histological criteria of intramuscular lipoma. Tumor presented as a single lesion measuring 10 cm in its greatest diameter, slowly growing over a period of 30 years. Clinical course of oral intramuscular lipomas is usually asymptomatic, but on rare occasions, the infiltration is so extensive that it can cause muscle dysfunction or sensory changes due to pressure on nerve trunks [5, 13]. In the present case the large size of the tumor interfered either with speech or swallowing. On CT scan, intramuscular lipoma shows a high density from 83 to 143 Hamsfield units with poorly defined margins. The magnetic resonance imaging can be useful. The strikingly high intensity signals on both T1- and T2-weighted images are suggestive of lipoma, and it further delineates the extent of tumour involvement [14]. In our case, a preoperative diagnosis of lipoma was suggested on CT scan features. Treatment of intramuscular lipoma is based on its complete surgical excision, whenever possible. The typical infiltrative growth pattern of intramuscular lipoma can be responsible of a potential misdiagnosis of malignancy. Differential diagnosis of intramuscular lipoma mainly revolves around liposarcoma. Unlike the latter, however, the former lacks lipoblasts, cellular pleomorphism, marked vascularisation and mitotic activity [15]. In our case, although adipocytes infiltrated striated muscle fibers, they were all mature and uniform in shape and size. In addition, no morphological worrisome feature of liposarcoma, previously mentioned, could be identified. Local recurrence of intramuscular lipoma has been observed in up 62.5% of the cases [16]. This high rate of recurrence is probably related to the difficulties in achieving radical surgical excision. After surgical treatment no recurrences of giant intramuscular lipoma are reported in the literature [10]-[12]. In our case, patient is well with no recurrence after a 15-month follow-up period. No future local recurrence is expected as a complete tumor excision was obtained.
