What is the differential diagnosis, appropriate work‑up, and management for a soft, non‑tender, mobile mass located just superior to the umbilicus in an adult?

Differential Diagnosis and Management of Soft, Non-Tender Periumbilical Mass

Begin with plain radiographs followed by ultrasound as the initial imaging approach for this superficial periumbilical mass, as this combination identifies the vast majority of benign lesions and guides further management. 1

Differential Diagnosis

The most likely diagnoses for a soft, non-tender, mobile mass above the umbilicus include:

• Lipoma - the most common soft tissue tumor, accounting for nearly half of all benign lesions 2
• Umbilical hernia - frequently underdiagnosed with a prevalence of 62.4% on CT imaging, often presenting as a palpable mass 3
• Epidermoid cyst - common superficial lesion with high ultrasound diagnostic accuracy 1
• Atypical lipomatous tumor (ALT) - if the mass is deep-seated or >5 cm, though rare in superficial locations 1, 4

Initial Work-Up Algorithm

Step 1: Plain Radiographs

Obtain radiographs first to identify:

• Intrinsic fat (present in 11% of soft tissue masses) 1
• Hernia defects or unsuspected skeletal abnormalities 1
• Calcifications or foreign bodies 1

Step 2: Ultrasound Examination

Proceed to ultrasound as the primary diagnostic tool for superficial masses, with sensitivity 94.1% and specificity 99.7% 1, 5:

For lipoma, look for:

• Hyperechoic or isoechoic appearance compared to surrounding fat 5, 6
• Thin, curved echogenic lines within an encapsulated mass 5
• Minimal to no internal vascularity on Doppler 5, 6
• No acoustic shadowing 1, 5

For hernia, identify:

• Fascial defect at the umbilicus 3
• Reducible content (fat or bowel) 7

For epidermoid cyst, note:

• Well-circumscribed anechoic or hypoechoic lesion 1
• Posterior acoustic enhancement 7

Red Flags Requiring Advanced Imaging or Urgent Referral

Obtain MRI urgently if any of the following are present:

• Size >5 cm in diameter 5, 8, 4
• Deep location (beneath deep fascia) 8, 4
• Rapid growth or increasing size 5, 8
• Pain or tenderness 8
• Atypical ultrasound features (heterogeneous echotexture, irregular margins, unexpected vascularity) 5, 6

These features raise concern for soft tissue sarcoma and warrant suspected cancer pathway referral within 2 weeks. 8

Management Based on Diagnosis

If Typical Lipoma (<5 cm, Superficial, Asymptomatic)

• Clinical observation is appropriate without imaging follow-up 5
• Excision only if symptomatic, rapidly growing, or patient preference 5

If Umbilical Hernia

• Surgical repair planning, particularly if symptomatic or enlarging 3
• CT may be obtained for surgical planning if complex 3

If Atypical Features or Diagnostic Uncertainty

Proceed to MRI to differentiate benign lipoma from ALT (accuracy up to 69%) 1, 5:

• Look for nodularity, thick septations, or stranding suggesting ALT 1, 5
• If MRI shows concerning features, obtain core needle biopsy with MDM-2 amplification analysis - this is the defining diagnostic test 1, 5
• MDM-2 positive confirms ALT and requires en bloc resection rather than simple excision 1

Critical Pitfalls to Avoid

• Do not assume all soft periumbilical masses are benign lipomas - umbilical hernias are frequently missed (64.8% underreporting rate on imaging) and can lead to complications if unrecognized during surgical approaches 3
• Do not rely on clinical examination alone - only 85% of lipomas are correctly identified by physical examination 1
• Do not skip radiographs - they remain the fundamental first step and provide diagnostic information in 62% of soft tissue masses 1
• Do not use ultrasound for deep-seated masses - accuracy drops precipitously for lesions outside subcutaneous tissue 1
• Do not perform excisional biopsy without imaging if the mass is >5 cm or deep, as unplanned excisions of sarcomas commonly occur due to presumptive lipoma diagnosis 4