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Updated: Jun 22 2021


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  • summary
    • Lipomas are common benign tumors of mature fat which may be subcutaneous, extramuscular, or intramuscular.
    • The condition is typically seen in patients 40-60 years of age who present with a stable, mobile, and painless mass.
    • Diagnosis is made with MRI studies showing a homogenous lesion with signal intensity matching adipose tissue on all image sequencing.
    • Treatment is observation for asymptomatic lesions. Marginal surgical resection is indicated for symptomatic lesions or lesions that are rapidly growing
  • Epidemiology
    • Demographics
      • slightly more common in men
      • affects predominantly patients between 40-60 years old
      • develops in sedentary individuals
    • Anatomic location
      • superficial/subcutaneous location is common
        • superficial lesions are common in the upper back, thighs, buttocks, shoulders and arms
        • deep lesions are affixed to surrounding muscle, in the thighs, shoulders and arms
      • ~5-10% of patients with a known superficial lipoma, will have multiple lesions
  • Classification
    • Common variants of lipoma include
      • spindle cell lipoma
        • common in male patients ages 45-65 years
        • stain positive for CD34 but negative for S-100
      • pleomorphic lipoma
        • common in middle aged patients
        • may be confused with liposarcomas
      • angiolipoma
        • unique in that it is painful when palpated
        • often present with small nodules in the upper extremity
      • intramuscular lipoma
        • often symptomatic and require marginal resection
      • hibernoma
        • tumor of brown fat
        • affects younger patients (20-40 years old)
  • Symptoms
    • Symptoms
      • usually a painless mass that has been present for a long time
        • exception is the angiolipoma, which is painful when palpated
    • Physical exam
      • palpable, mobile, painless lesion
  • Imaging
    • Radiographs
      • may show a radiolucent lesion in the soft tissues
      • may see mineralization, which should raise concern for synovial cell sarcoma
        • may see calcifications or presence of bone within the lesion
    • CT scan
      • well demarcated lesion
      • lesion looks akin to subcutaneous fat
    • MRI
      • well demarcated lesion
      • homogenous, signal intensity matches adipose tissue on all image sequencing
      • shows well demarcated lesion with same characteristics as mature fat
        • high signal intensity on T1 weighted images
        • high signal intensity on T2 weighted images, entirely suppressed by STIR or fat saturated sequences
        • low signal intensity on STIR image
  • Histology
    • Biopsy often not necessary as diagnosis can be made by imaging (MRI)
    • Gross appearance
      • Lipomas are soft, lobular, may be encapsulated and whitish/yellowish in color
      • Hibernoma are reddish brown because of rich vascular supply in addition to high numbers of mitochondria
    • Histology in general shows bland acellular stroma with neoplastic cells that lack cellular atypia.
    • Histology varies by variant
      • spindle cell lipoma
        • mixture of mature fat cells and spindle cells
        • mucoid matrix with varying number of birefringent collagen fibers
      • pleomorphic lipoma
        • lipocytes, spindle cells, and scattered atypical giant cells
      • angiolipoma
        • mature fat cells with nests of small arborizing vessels
      • intramuscular lipoma
        • pathology shows lipoblasts and muscle infiltration
  • Treatment
    • Nonoperative
      • observation only
        • indications
          • lesion is painless and MRI is determinate for a benign fatty lesion
    • Operative
      • marginal resection (may be intralesional)
        • indications
          • symptomatic lesions
          • mass is rapidly growing
          • tumors located deep to the fascia or in the retroperitoneum
            • deep or retroperitoneal lipomas show a higher likelyhood to be/become atypical lipomatous tumors
            • in the retroperitoneum, referred to as well-differentiated liposarcoma
            • in the extremities, referred to as atypical lipomas
          • spindle cell/pleomorphic lipomas are treated by marginal resection
  • Complications
    • Local recurrence
      • uncommon (< 5%)
  • Prognosis
    • Size typically plateaus after initial growth
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