Updated: 10/6/2016

Lipomas

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Introduction
  • A common benign tumor of mature fat
    • may be subcutaneous, extramuscular, or intramuscular 
  • Epidemiology
    • demographics
      • slightly more common in men
      • affects predominantly patients between 40-60 years old 
      • develops in sedentary individuals
    • 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
  • Prognosis
    • size typically plateaus after initial growth
Classification
  • Common variants of lipoma include
    • spindle cell lipoma
      • common in male patients ages 45-65 years
    • 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%) 
 

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Questions (8)
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(OBQ09.27) After months of right shoulder pain, a 70-year-old man undergoes work up of a right arm mass with a MRI and also has a CT of his chest/abdomen/pelvis. A representative MRI image is shown in Figure A. He has difficulty using his arm because of the increasing size of the mass. The CT scans shows no evidence of metastatic disease. What is the next step in management? Review Topic

QID: 2840
FIGURES:
1

Core biopsy

33%

(611/1847)

2

Radiation therapy

0%

(9/1847)

3

Chemotherapy followed by surgery

1%

(18/1847)

4

Observation

1%

(13/1847)

5

Surgical excision

65%

(1193/1847)

ML 3

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(OBQ07.254) A 55-year-old man complains of chronic pain and fullness in his proximal posterior thigh that is worse with sitting. Radiograph, MRI, and biopsy are shown in Figures A, B, C, and D, respectively. What is the most likely diagnosis? Review Topic

QID: 915
FIGURES:
1

Dedifferentiated liposarcoma

9%

(78/874)

2

Fibrosarcoma

1%

(11/874)

3

Intramuscular Lipoma

88%

(769/874)

4

Infection

0%

(1/874)

5

Chordoma

1%

(11/874)

ML 1

Select Answer to see Preferred Response

PREFERRED RESPONSE 3
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