Hyperechoic Muscle Mass
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Helpful Clues for Common Diagnoses
Located deep to investing fascia
May be classified as subfascial, intermuscular, intramuscular, or submuscular in location
US appearances of deep lipomas are similar to subcutaneous lipomas but more variable
Discrete noninfiltrative mass with well-defined convex margins
Fusiform or oblong in shape with long axis parallel to skin
May be hypoechoic (infrequent)
Fine linear echogenic striations running parallel to long axis of tumor in both transverse and longitudinal planes
May show acoustic enhancement as US transmission in fat > muscle
No vascularity in or around lipoma on color Doppler
Consider malignancy if the following features are present
4 distinct histologic types of liposarcoma
MR is helpful for surgical planning and establishing baseline for all deep-seated lipomas
Vascular malformation and hemangioma indistinguishable on US
Hemangioma
Vascular malformation
5 different subtypes of vascular malformation depending on predominant vascular component
US is helpful in establishing diagnosis, assessing flow, and determining relative amount of stroma vs. vascular component
Intramuscular hematoma may occur due to trauma, anticoagulation, vascular malformation, or sarcoma
Acute hematoma is usually isoechoic or hyperechoic to muscle
Mild diffuse intramuscular hemorrhage may be overlooked on US, as ill-defined hyperechoic areas blend with muscle
Remember that intramuscular sarcomas or vascular malformations may bleed spontaneously or during exercise
Helpful Clues for Less Common Diagnoses
Lodges in subcutaneous tissues much more commonly than in muscle
Nearly all foreign bodies are echogenic
± reverberation artifact or acoustic shadowing
Bamboo and noncompact wood are difficult to see because they absorb fluid and have echogenicity similar to soft tissue
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