Re: Giant Hand Lipoma Revisited: Report of a Thenar Lipoma and its Literature Review

Dear Editor, Lipoma is the most common mesenchymal tumor. Although very common in other regions of the body, its occurrence in the hand is not as common. Some authors designate lipomas greater than 5 cm as giant lipomas. We recently read, with great interest, an article named “Giant hand lipoma revisited: Report of a thenar lipoma and its literature review” published in the Journal of Hand and Microsurgery [1]. In this letter to the editor, we would like to comment on a few important points regarding this specific article. First, we believe that although the size of the lipoma is important, the anatomical location is even more important when considering treatment and prognosis. Generally, lipomas can be divided into superficial or deep-seated. Deep-seated lipomas are located under the fascia and some of them can be further categorized into two very important subgroups: intermuscular and intramuscular lipomas. Frequently, deep-seated lipomas can grow to a large size and, therefore, the cutoff of 5 cm may not accurately represent their average size. In a study of thirteen deep-seated lipomas of the upper limb, Elbardouni et al. found that the mean size was 7 cm ranging from 5 to 20 cm [2]. In addition, Lee et al. in a sample of 6 intramuscular lipomas of the thenar and hypothenar muscles found the average size to be above 5 cm [3]. Although further evidence is needed to define the size of deep-seated lipomas in general and the hand in particular, size larger than 5 cm may be common and not necessarily represent malignancy. Furthermore, we believe that simply classifying the lipoma as “giant” may be confusing when no further description is provided. Perhaps, terms like “intermuscular giant lipoma”, “intramuscular giant lipoma” or “deep-seated giant lipoma” should be used instead. This is more descriptive and will address the location as well as the size of the tumor. Also, intermuscular lipomas are usually well encapsulated and grow expansively compared to intramuscular lipomas; the majority of which tend to grow infiltratevly. The term “infiltrative lipoma”, which has been used to describe these two subgroups, should be used only with the tumors which disclose infiltrative features to adjacent tissues. Second, the authors of this article state that “many of the giant lipomas have well-differentiated liposarcomatous components, which are difficult to differentiate form their benign counterpart”. Lipomas do not have well-differentiated liposarcomatous components regardless of their size. Even malignant transformation of a pre-existing mesenchymal tumor, including lipoma, has been questioned for a long time [4]. It is true, however, that it can be difficult to differentiate lipoma clinically, histologically and on imaging from well-differentiated liposarcoma. Insufficient sampling of a well-differentiated liposarcoma may erroneously misinterpret this neoplasm for lipoma and a radiologist who is inexperienced with that type of pathology may confuse the infiltrative intramuscular lipoma with liposarcoma [5]. In questionable cases, cytogenetic testing has been useful to differentiate the two groups on the bases of specific chromosomal aberrations. In conclusion, we believe that the term “giant lipoma” should be used in conjunction with other more descriptive terms such as “intramuscular”, “intermuscular” and “deep-seated” when referring to this pathology. Careful pre-surgical imaging evaluation may be pathognomonic in the majority of cases. Thorough histological examination and cytogenetic testing may avoid misdiagnosis of well-differentiated liposarcoma with deep-seated lipoma.