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INTRODUCTION

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Benign soft tissue tumors and reactive lesions are encountered frequently in Surgical Oncology practice. While benign, these lesions often cause local symptoms, and they may mimic or be confused with malignant lesions. In these cases, surgical management is required to establish the diagnosis. Table 29-1 shows a comprehensive list of benign and reactive entities. This chapter will focus on those most frequently encountered in clinical practice.

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Table Graphic Jump Location
TABLE 29-1:

Comprehensive List of Benign Soft tissue Tumors and Reactive Lesions

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BENIGN SOFT TISSUE TUMORS

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Lipoma

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BACKGROUND
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Lipomas are the most common benign soft tissue tumor overall. They are fatty tumors that most often develop in the subcutaneous tissue of the trunk and proximal extremities; however, they can occur in deep sites including within muscle, and in the retroperitoneum and gastrointestinal (GI) tract. Lipomas are usually solitary lesions but approximately 2% of patients may present with multiple lesions that may or may not exhibit a familial pattern. No environmental risk factors for solitary lipomas have been identified.

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MOLECULAR BIOLOGY/PATHOLOGY
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Benign lipomas are characterized by specific molecular aberrations including translocations of 12q13-15 or rearrangements involving 13q or 6p21-33.1 Histologically, they are composed of enlarged adipocytes arranged in a well-encapsulated, lobular mass with a thin fibrous capsule (Fig. 29-1).

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FIGURE 29-1:

Gross image of subcutaneous lipoma demonstrating encapsulated, lobular appearance that is typical of these lesions.

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CLINICAL MANIFESTATIONS
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Patients often present with a soft, mobile, palpable mass in the subcutaneous tissue and will often report very slow or no growth over time. Intramuscular lipomas present as more of a generalized swelling than a discreet mass given their deeper location. They are usually not well encapsulated but are more infiltrative into the surrounding muscle fibers. Lipomas are usually painless and asymptomatic. GI tract lipomas may also be diagnosed incidentally, but occasionally cause intussusception, obstruction, or GI bleeding.

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DIAGNOSTIC EVALUATION
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Small, subcutaneous lipomas are often apparent on physical examination and no imaging studies are required. Cross-sectional imaging with computed tomography (CT) or magnetic resonance imaging (MRI) is helpful in assessing deep-seated lesions and intramuscular lesions. Regardless of location, most benign lipomas appear as homogenous, well-circumscribed, unilobular fatty masses. On CT, they have attenuation of −70 to −150 Hounsfield units (HU)2 (Fig. 29-2). GI tract lipomas share these same characteristics on cross-sectional imaging. They are soft ...

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