Lipomas are common, benign growths composed of fatty tissue, often found just beneath the skin. These soft, movable lumps are generally painless, though they can cause discomfort if they press on nerves or blood vessels. When a new lump appears, medical evaluation is often sought, and ultrasound frequently serves as a primary imaging method for assessment.
How Ultrasound Identifies Lipomas
Ultrasound helps identify features consistent with a lipoma. These benign fatty tumors appear as well-defined, oval or round structures. Their internal structure is homogeneous, appearing uniform.
Lipomas often appear hypoechoic or isoechoic compared to surrounding muscle, meaning they are darker or similar in brightness. However, some, particularly in the head and neck, can appear hyperechoic, or brighter, than adjacent muscle. Thin, bright lines (echogenic lines or striations) often run parallel to the skin surface within the mass, representing fibrous septa characteristic of fatty tissue. The absence of significant blood flow on color Doppler ultrasound also supports a benign diagnosis.
Accuracy and Diagnostic Challenges
Ultrasound is effective for diagnosing typical lipomas, with an accuracy rate often between 80% and 95%. This makes it a preferred initial imaging modality. While many lipomas present with classic sonographic features, their appearance can vary, including hyperechoic, isoechoic, or hypoechoic relative to surrounding muscle.
The primary challenge is distinguishing a benign lipoma from other soft tissue masses, especially liposarcomas, which are rare malignant fat cell tumors. Although ultrasound can help differentiate them, some imaging features overlap, making a definitive diagnosis based solely on ultrasound challenging in atypical cases. For instance, while lipomas usually show no or minimal blood flow, a heterogeneous appearance or more than minimal color Doppler flow can raise suspicion for a liposarcoma.
When Additional Imaging or Biopsy is Necessary
Certain features on clinical examination or ultrasound can raise suspicion for a more concerning diagnosis, requiring further investigation. These “red flags” include rapid growth, a size greater than 5 centimeters, firm consistency, or if the mass feels fixed to underlying tissues. Recurrence after surgical removal also warrants scrutiny.
In atypical cases, healthcare providers may recommend additional imaging studies for a more detailed understanding of the mass. Computed Tomography (CT) scans provide cross-sectional images and help identify calcifications. Magnetic Resonance Imaging (MRI) offers superior soft tissue contrast and is useful for larger or deeper lesions. Ultimately, if suspicion for malignancy remains, a biopsy (taking a tissue sample for microscopic examination) may be required for a definitive diagnosis.