Focused Abdominal Wall Ultrasound
For a soft superficial abdominal wall mass, order a focused abdominal wall ultrasound (not a complete abdominal ultrasound), as ultrasound is the recommended first-line imaging modality for superficial soft tissue masses with sensitivity of 94.1% and specificity of 99.7%. 1, 2
Initial Imaging Algorithm
Step 1: Consider Plain Radiographs First
- Plain radiographs should technically precede ultrasound for any soft tissue mass to identify calcifications, bone involvement, or intrinsic fat 1, 3
- However, radiographs have significant limitations for soft superficial abdominal wall masses—they are often unrewarding when the mass is small, non-mineralized, or superficial 1
- Radiographs identify intrinsic fat in only 11% of soft tissue masses 2, 3
- In practical terms, you can proceed directly to ultrasound for a clearly superficial, soft abdominal wall mass 1, 4
Step 2: Order Focused Abdominal Wall Ultrasound
- Ultrasound is most useful when applied specifically to superficial lesions (those superficial to the deep fascia) 1
- The diagnostic accuracy of ultrasound is considerably less when deep lesions are included, so a focused study on the palpable superficial mass is appropriate 1
- A complete abdominal ultrasound is unnecessary and not indicated for evaluating a superficial abdominal wall mass 1, 5
- Ultrasound can confirm the presence of a mass, differentiate solid from cystic lesions, and assess vascularity 1, 6
What Ultrasound Will Determine
For Lipomas (Most Common Scenario)
- Characteristic features include hyperechoic appearance, thin curved echogenic lines within an encapsulated mass, minimal to no vascularity on Doppler, and no acoustic shadowing 1, 2, 7
- When these typical features are present, no further imaging is needed 2, 7
- Lipomas account for approximately 96% of superficial soft tissue masses 7
Red Flags Requiring Advanced Imaging
If ultrasound shows ANY of the following, proceed to MRI with and without contrast: 1, 7
- Size >5 cm
- Deep (subfascial) location
- Atypical features (thick septations >2mm, nodularity, soft tissue components)
- Uncertain or inconclusive findings
- Significant vascularity suggesting something other than lipoma
Common Pitfalls to Avoid
- Do not order a "complete abdominal ultrasound"—this examines intra-abdominal organs (liver, gallbladder, kidneys, etc.) and is not designed to evaluate the abdominal wall itself 5
- Physical examination alone correctly identifies only 85% of soft tissue masses, so imaging confirmation is essential 2, 3
- Ultrasound is highly operator-dependent; if the sonographer or radiologist is uncertain, MRI should follow 1
- For any retroperitoneal or intra-abdominal mass (not superficial abdominal wall), CT or MRI is preferred and the patient should be referred to a sarcoma multidisciplinary team before surgery 1, 7
When to Escalate Beyond Ultrasound
- If the mass is increasing in size, deep-seated, or located in the lower abdomen/groin, there is heightened concern for atypical lipomatous tumor (well-differentiated liposarcoma) requiring MRI 1, 7
- MRI can differentiate benign lipomas from atypical lipomatous tumors in up to 69% of cases 7
- Any mass with pain, rapid growth, firm consistency with irregular margins, or atypical ultrasound features warrants MRI 7