Intermuscular lipoma

Last revised by Mohammadtaghi Niknejad on 03 Aug 2022

Intermuscular lipomas are lipomas located deep between muscles.

Intermuscular lipomas are sometimes called ‘infiltrating lipomas’ since they can involve both the intramuscular and the tissue between muscles 1.

Intermuscular lipomas are much less common than superficial lipomas and are found most often in middle-aged patients from the 4th to 6th decades of life, with men being more commonly affected 1-3

They might be found incidentally, or patients might present with a palpable nonspecific lump. They are usually larger on clinical presentation than superficial lipomas 1,2.

Lipomas consist of mature adipocytes identical to normal adult fatty tissue 1

Intermuscular lipomas are most often found between large muscles of the following locations 1,2:

  • lower extremity
  • trunk
  • shoulder
  • upper extremity

Intermuscular lipomas of the chest wall, hand, and feet are rare as well as in the retroperitoneum.

Intermuscular lipomas are usually yellowish, well-circumscribed lesions surrounded by a thin capsule located between muscles 1.

Histologically adipocytes of intermuscular lipomas are usually larger, possibly with microscopic, neighboring muscular infiltration 1,2.

A large intermuscular lipoma can appear as lucency on a plain radiograph.

Intermuscular lipomas usually show the following features 1:

  • homogeneous, hypodense soft tissue mass within the musculature
  • typically with Hounsfield measurements in the -60 to -120 range
  • frequently show thin septae

MRI usually shows a fat-containing homogeneous mass within a muscle, which is isointense to subcutaneous fat in all sequences, frequently showing subtle thin intralesional septae 1.

  • T1: homogeneous, high signal intensity
  • T2: homogeneous, high signal intensity
  • T2FS/IMFS: homogeneous, low signal intensity
  • T1C+: no enhancement, except for possible subtle enhancement of the fibrous capsule

Treatment options depend on tumor size, location symptoms, and overall patient condition and include wide resection, which is curative.

Differential diagnosis includes the following 2:

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Cases and figures

  • Case 1: anterior abdominal wall
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  • Case 2: arm
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  • Case 3: neck
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  • Case 4: back
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  • Case 5: axillary
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