What are the typical ultrasound features of a lipoma?

Ultrasound Features of Lipomas

On ultrasound, lipomas typically appear as well-circumscribed, hyperechoic masses arising from the submucosa (third layer) with homogeneous internal echogenicity. 1, 2

Key Sonographic Characteristics

• Location and Layer of Origin: Lipomas most commonly arise from the submucosal layer (third layer) on endoscopic ultrasound 1

• Echogenicity: Lipomas appear intensely hyperechoic compared to surrounding tissues 1, 2

• Margins: Well-defined, smooth borders with an encapsulated appearance 2, 3

• Internal Structure:

  • Homogeneous internal echogenicity in approximately 66% of cases 3
  • May contain thin, curved echogenic lines within the mass 1, 4
  • Minimal to no internal vascularity on Doppler examination 1, 5

• Shape: Often elongated with the greatest diameter parallel to the skin surface (for superficial lipomas) 3, 6

• Additional Features:

  • Some lipomas (27%) may show a hypoechoic capsule surrounding the hyperechoic content 6
  • No acoustic shadowing is typically observed 1

Diagnostic Confidence

• The sonographic appearance of lipomas can vary:

  • 29-34% appear hyperechoic 3, 6
  • 22-24% appear isoechoic 3, 6
  • 26-29% appear hypoechoic 3, 6
  • 16-20% show mixed echogenicity 3, 6

• When combined with endoscopic evaluation, the "pillow sign" (indentation when pressed with biopsy forceps) is highly suggestive of a lipoma with 98% specificity 1, 2

Differentiating from Malignancy

• Features suggesting possible well-differentiated liposarcoma rather than benign lipoma include:
  • Deep location (below muscular fascia)
  • Irregular shape
  • Large diameter
  • Presence of internal vascularity on Doppler
  • Heterogeneous appearance 5

Clinical Relevance

• Endoscopic ultrasound (EUS) is the modality of choice for evaluating subepithelial lesions including lipomas 1

• For superficial lipomas, conventional ultrasound provides accurate identification with high sensitivity (94.1%) and specificity (99.7%) 1

• When ultrasound features are typical (hyperechoic, well-circumscribed, minimal vascularity), further imaging may not be necessary 1, 2

• Atypical features warrant additional evaluation, which may include contrast-enhanced imaging or tissue sampling 1