Lipomas

Author: Amiethab Aiyer

Topic updated on 03/10/13 6:51pm

Introduction

A common benign tumor of mature fats
- 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 lesion
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 (bright) on T1 weighted images
  - low signal intensity (dark) on T2 weighted images
  - low signal intensity (dark) 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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TAG

(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? Topic

Review Topic

FIGURES: A

1. Core biopsy
2. Radiation therapy
3. Chemotherapy followed by surgery
4. Observation
5. Surgical excision

PREFERRED RESPONSE ▶

DISCUSSION: The T-1 weighted MRI shows a soft tissue homogeneous mass that has the same signal intensity as fat, and is intramuscular. Based on the history in the stem, and the imaging provided, the patient has an intramuscular lipoma. These are slow growing and painless. Biopsy of these lesions is not necessary because the diagnosis can usually be made on MRI. Dalal et al provide a review of lipomatous masses, commenting that lipomas are very common and comprise 50% of soft tissue neoplasms, and that marginal surgical excision is the treatment and recurrence rates range from 15-60%.

REFERENCES:

1. Schwartz HS (ed): Orthopaedic Knowledge Update: Musculoskeletal Tumors 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2007, pp 277-287

2. Dalal KM, Antonescu CR, Singer S. Diagnosis and management of lipomatous tumors. J Surg Oncol. 2008 Mar 15;97(4):298-313. PMID:18286473 (Link to Abstract)

Question Authors:

Khalid Yousuf MD, John Badylak MD,

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TAG

(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? Topic

Review Topic

FIGURES: A

1. Dedifferentiated liposarcoma
2. Fibrosarcoma
3. Intramuscular Lipoma
4. Infection
5. Chordoma

PREFERRED RESPONSE ▶

DISCUSSION: The clinical presentation is consistent with a intramuscular lipoma. The radiograph shows a soft tissue density on the left side. The axial MRI images reveals a mass within the gluteus maximus that is bright on T1 and dark on the STIR image. The pathology shows lipoblasts and muscle infiltration which is characteristic of these tumors. The cited reference by Damron et al reviews common soft tissue masses seen by orthopaedic surgeons. They outline an algorithm for evaluation and management of both benign and malignant tumors. Treatment for intramuscular lipomas involves surgical resection only if symptomatic, as these tumors are benign. Matsumoto et al reviewed MRI findings of intramuscular lipomas and found that imaging characteristics varied from a homogeneous mass as commonly seen in an ordinary (superficial) lipoma, to a large, inhomogeneous lesion with an infiltrative margins. Infiltrative margins did not indicate malignancy.

REFERENCES:

1. Damron TA, Beauchamp CP, Rougraff BT, Ward WG Sr. Soft-tissue lumps and bumps. JBJS (American) 85:1142-1155 (2003) PMID:15116652 (Link to Abstract)

2. Matsumoto K, Hukuda S, Ishizawa M, Chano T, Okabe H. MRI findings in intramuscular lipomas. Skeletal Radiol. 1999 Mar;28(3):145-52. PMID:10231912 (Link to Abstract)

Question Authors:

Jan Szatkowski MD, Derek Moore, Guillem Lomas MD,

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ABOS II: Lipomas

General - Oral Boards Review

7/29/2011

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Evidence & References Show References

Level of Evidence 4 (Case Series)

Matsumoto K, Hukuda S, Ishizawa M, Chano T, Okabe H. MRI findings in intramuscular lipomas. Skeletal Radiol. 1999 Mar;28(3):145-52. PMID:10231912 (Link to Abstract)

Textbooks

Review of Orthopaedics, 6th Edition, Mark D. Miller MD, Stephen R. Thompson MBBS MEd FRCSC, Jennifer Hart MPAS PA-C ATC, an imprint of Elsevier, Philadelphia, Copyright 2012
AAOS Comprehensive Orthopaedic Review, Jay R. Leiberman. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2009
Orthopaedic Knowledge Update 10, John M Flyn. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2011
Hoppenfeld SP. Surgical Exposures in Orthopaedics: The Anatomic Approach. Lipponcott, Williams, and Wilkins, Philadelphia, PA, Copyright 2009
Orthopaedic In-training Examination (OITE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
Self-Assessment Examination (SAE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012

Undefined

Dalal KM, Antonescu CR, Singer S. Diagnosis and management of lipomatous tumors. J Surg Oncol. 2008 Mar 15;97(4):298-313. PMID:18286473 (Link to Abstract)
Damron TA, Beauchamp CP, Rougraff BT, Ward WG Sr. Soft-tissue lumps and bumps. JBJS (American) 85:1142-1155 (2003) PMID:15116652 (Link to Abstract)
Schwartz HS (ed): Orthopaedic Knowledge Update: Musculoskeletal Tumors 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2007, pp 277-287

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Lipomas

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