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Liposarcoma Associated With Multiple Intramuscular Lipomas: A Case Report

Matsumoto, Keiji*; Hukuda, Sinsuke*; Ishizawa, Michihito*; Egawa, Masaaki*; Okabe, Hidetoshi**

Clinical Orthopaedics and Related Research: April 2000 - Volume 373 - Issue - p 202-207
Section II: Original Articles: Tumor

A 71-year-old slender, previously healthy man was admitted to the authors' institution because of a huge painless mass in his left scapular area. Physical examination revealed a second soft tissue mass in his right scapular region and a third soft tissue mass in the anterior side of his right shoulder. Surgical treatment including marginal resection of the second and third small masses followed by wide local resection of the huge tumor was performed. Histologic examination showed that the first mass was a well differentiated lipomalike liposarcoma, whereas the second and third lesions were identified as intramuscular lipomas. A review of the literature showed two cases of retroperitoneal liposarcoma associated with multiple subcutaneous lipomas and two cases of liposarcoma involving an extremity associated with multiple subcutaneous lipomas. There is no previous report in which intramuscular liposarcoma was associated with multiple intramuscular lipomas.

From the *Department of Orthopaedic Surgery and **Division of Surgical Pathology, Shiga University of Medical Science, Otsu, Shiga, Japan.

Reprint requests to Keiji Matsumoto, MD, Department of Orthopaedic Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.

Received: February 16, 1999.

Revised: June 24, 1999.

Accepted: July 27, 1999.

Well differentiated liposarcoma is a common malignant soft tissue tumor in middle-aged to elderly patients.5 However, intramuscular lipoma is a rare benign lipomatous neoplasm that arises in muscle tissue.1,3-5,8,9,11,12 The coexistence of these two lipomatous tumors is unusual. The authors report a patient with well differentiated intramuscular liposarcoma in the left trapezius muscle associated with multiple intramuscular lipomas in the right trapezius muscle and right deltoid muscle. No previous study has reported intramuscular liposarcoma and multiple intramuscular lipomas in one patient. The possible pathogenesis of the coexistence of these deep seated lipomatous tumors is discussed.

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A 71-year-old slender previously healthy man, who had been working as a construction laborer, was admitted to the authors' institution because of a huge painless mass in his left scapular area. He had noticed an egg sized mass 7 years before in this region. The gradual growth of the mass and dull pain around the lesion caused him to visit the authors' institution. His family and medical histories were unremarkable.

Physical examination revealed a huge (24 × 24 cm) soft tissue tumor at the left scapular region. The mass adhering to the scapula was elastic, soft, slightly warm, and nontender. A second soft tissue mass (5 × 5 cm) in his right scapular region and a third soft tissue mass (4 × 2.5 cm) in the anterior side of his right shoulder also were detected. These two masses were soft; however, they became apparent and firm with involved muscle contraction (Fig 1). Laboratory examination including fat metabolism studies revealed no abnormal findings.

Fig 1A

Fig 1A

Axial T1 and T2 weighted magnetic resonance imaging (MRI) showed a huge soft tissue tumor in his left trapezius muscle of high signal intensity associated with linear structures of low signal intensity in the content (Fig 2A). These structures were well enhanced on T1 weighted fat suppressed images after injection of gadolinium diethylenetriamine pentaacetic acid (DTPA). Sagittal T1 weighted images revealed nodules of intermediate signal intensity in the inferior and medial parts of the lesion (Fig 2B). These nodules showed high signal intensity on T2 weighted images and were well enhanced after injection of gadolinium DTPA. Magnetic resonance findings also showed that the second small mass was composed of pure fatty tissue in the right trapezius muscle (Fig 2A). Computed tomography (CT) scans showed lipomatous tumors of low attenuation in the left trapezius muscle (the first lesion) and in the right deltoid muscle (the third lesion) (Fig 3). Gallium scans showed moderate uptake only in the first huge mass in the left trapezius muscle. Needle biopsy of the first mass failed to show the malignant nature of the lesion; however, the diagnosis of liposarcoma was established based on the previously reported MRI findings and the authors' study of borderline lipomatous tumors.10,12 In brief, the latter study showed that lipomatous lesions composed of interrelated tumor masses (multinodular lesion) on MRI were malignant. The preoperative diagnosis of the huge mass was well differentiated liposarcoma with suspected dedifferentiated foci, whereas the second and third masses were considered to be intramuscular lipomas.

Fig 2A

Fig 2A

Fig 3

Fig 3

Surgical treatment including marginal resection of the two small masses followed by wide local resection of the huge tumor was performed on June 16, 1998. Because the first lesion was intracompartmental, the distal half of the involved trapezius muscle was resected en bloc with the underlying fascias and superficial halves of the muscle tissue of infraspinatus, supraspinatus, and rhomboideus. The skin including the needle biopsy tract also was resected en bloc. Macroscopic examination revealed that all three lesions were composed of mature lipomatous tissue. Careful observation of the cut surface of the first mass failed to detect any dedifferentiated foci. Histologic examination revealed that the huge tumor was composed of mature and benign looking lipocytes; however, some tumor cells contained slightly irregular cytoplasm and nuclei. Thick fibrous septa between lipomatous lobules, variation in the size and shape of the fat cells, and scattering of lipoblasts also were seen in several portions (Fig 4A). Mitotic activity was not evident, and there were no dedifferentiated foci. Based on these histologic findings, the diagnosis of well differentiated lipomalike liposarcoma was established. However, the second and third lesions were identified as intramuscular lipomas containing mature and benign lipocytes (Fig 4B). Careful observation failed to reveal lipoblasts or malignant cells in these lesions.

Fig 4A

Fig 4A

The postoperative course was uneventful. The patient was doing well without local recurrence of any masses 10 months after the surgery; however, a fourth small lesion identical to intramuscular lipoma was detected by MRI in the abdominal muscle at the last followup.

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The diagnosis of the first large mass in the patient reported here was well differentiated lipomalike liposarcoma. However, it should be differentiated from other unusual fatty tumors, including spindle cell lipoma, pleomorphic lipoma, and atypical lipoma, in the current clinical setting. According to Enzinger and Weiss,5 spindle cell lipoma is a histologically distinct type of lipoma that is characterized by replacement of mature fat by collagen forming spindle cells. It occurs mainly in male patients between 45 and 65 years of age and is found chiefly in the regions of the posterior neck and shoulder. It manifests as a solitary, circumscribed or encapsulated, painless, firm nodule in the deep subcutis. Multiple lesions are rare but have been reported. The lesions average in size between 3 and 5 cm. Lipocytes are rare or absent, and the spindle cells dominate the histologic picture. Pleomorphic lipoma closely simulates a pleomorphic or sclerosing liposarcoma but most likely represents a benign, exceedingly pleomorphic variant of spindle cell lipoma. Pleomorphic lipoma also occurs as a circumscribed subcutaneous mass in the shoulder and neck region of men older than 45 years.5 All of the tumors in the current patient were located not in the subcutis but in the muscle tissue. Histologically, the lesions lacked the spindle cell pattern that is seen in spindle cell lipoma. Characteristic floretlike giant cells also were absent in the current lesions, although these cells are not specific of pleomorphic lipoma.5

Evans et al6 proposed the term atypical lipomas for all of the tumors formerly classified as well differentiated liposarcoma. Thus, atypical lipoma and well differentiated liposarcoma may be histologically indistinguishable. These authors additionally subclassified atypical lipomas into two categories: subcutaneous (atypical lipoma) and deep (atypical intramuscular lipoma). Atypical lipomas predominantly involved the neck and upper trunk, whereas the most common site of atypical intramuscular lipomas was the thigh.6 According to the subclassification, the huge mass seen in the patient in the current report may be not an atypical (subcutaneous) lipoma but an atypical intramuscular lipoma because of its location. However, Enzinger and Weiss5 suggested that the term "well differentiated liposarcoma" should be retained for all well differentiated liposarcomas that arise in deep soft tissues. That is because the biologic behavior of atypical (subcutaneous) lipomas differs from that of atypical intramuscular lipomas. The current authors agree with this opinion, and the final diagnosis of well differentiated liposarcoma was established.

Histologically, three subtypes of well differentiated liposarcoma can be distinguished: well differentiated lipomalike liposarcoma; well differentiated inflammatory liposarcoma; and well differentiated sclerosing liposarcoma.5 Well differentiated lipomalike liposarcoma is the most common type of well differentiated liposarcoma. It closely simulates lipoma, except for a scattering of lipoblasts with one or more lipid droplets in the cytoplasms, irregularly shaped cells with hyperchromatic nuclei, and lipocytes that have a slightly greater variation in size and shape than those of normal fat.5 These findings were observed in the large mass in the patient reported here. Complete excision with small margins may be adequate for the subcutaneous tumors (atypical lipomas), whereas a wider surgical margin is required for the treatment of well differentiated liposarcoma (atypical intramuscular lipomas) occurring in deep soft tissues. The latter may recur but never develop metastases.5 The rate of metastasis in liposarcoma is related closely to the degree of histologic differentiation.5 Well differentiated liposarcoma has the lowest metastatic activity, and a good prognosis is expected after appropriate wide local resection.

Lipoma is a common soft tissue tumor, whereas the intramuscular variant is relatively rare.1,3-5,8,9,11,12 Approximately 5% to 8% of patients with ordinary (subcutaneous) lipomas have multiple lesions.5 Multiple subcutaneous lipomas vary from a few to several hundred lesions and occur predominantly in the upper half of the body. Hyperlipidemia with high serum levels of cholesterol was reported in some patients5; however, the fat metabolism was normal in the patient of the current study. In addition, no previous study has reported multiple intramuscular lipomas to the authors' best knowledge. Although symmetric involvement of superficial lipoma is not an infrequent occurrence, the localization of one of the intramuscular lipomas and the liposarcoma was symmetric in the current case.

The involvement of well differentiated intramuscular liposarcoma in association with multiple intramuscular lipomas is unusual. There is no report in which intramuscular liposarcoma was associated with multiple intramuscular lipomas. A literature review also showed two cases of liposarcoma of an extremity associated with multiple subcutaneous lipomas.14 In addition, in rare cases, retroperitoneal liposarcoma has been associated with one or more lipomas at other sites.2,7 These authors considered that the occurrence of multiple lipomas in association with liposarcoma was attributable to the reaction of the adipose tissue as a whole to unknown tumor producing stimuli14 or common derangement of adipose tissue.2

The authors of the current study speculate there are three theoretical explanations for the pathogenesis of the current case. One is that the liposarcoma was the result of malignant transformation from one of the preexisting multiple intramuscular lipomas. The second is that the coexistence of benign and malignant lipomatous tumors was coincidental. The final explanation is that the two small masses were not intramuscular lipomas but metastatic lesions without marked malignant lipoblasts from the huge and longstanding liposarcoma. The first theory is the most likely explanation for this patient because the symmetric localization of the first (liposarcoma) and second (intramuscular lipoma) masses suggest that the coexistence of these lesions was not coincidental. In addition, well differentiated liposarcoma is a locally aggressive low grade malignant tumor with little metastatic activity.

Malignant transformation in a preexisting lipoma is rare, and only a few cases have been reported previously.13,15 Some of these were considered to be benign lipomas associated with focal myxoid, spindle cell, and pleomorphic areas. Others were well differentiated liposarcomas containing a lipomalike portion and a poorly dedifferentiated area (dedifferentiated liposarcoma).5 There were three lipomatous lesions around the shoulder joints in the current patient. One was well differentiated liposarcoma, and the others were intramuscular lipomas. Trauma is reported to be one of the possible etiologic factors in ordinary lipomas and in liposarcomas.5 The patient reported here was a construction laborer who received repetitive minor trauma at the shoulder and scapular regions. There may be a relationship between the patient's occupation and involvement of multiple lipomatous tumors around the shoulder. The authors speculate that the multiple intramuscular lipomas initially developed because of repetitive minor trauma or another unknown cause. The symmetric localization of the intramuscular lipoma and the liposarcoma suggests that one of the benign lesions may have transformed secondarily into a malignant tumor, but definitive evidence is lacking.

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The authors thank Masahiro Nabae, MD, and Seiji Hiraoka, MD, for their contribution to this work.

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