What is the diagnosis and treatment for a 24-year-old patient presenting with superficial horizontal linear lumps on the skin surface of the left iliac fossa, which are non-painful and appear and disappear at random times?

Superficial Linear Lumps on Left Iliac Fossa: Diagnosis and Management

Most Likely Diagnosis

This presentation is most consistent with a superficial lipoma or lipomatosis, though the transient nature raises consideration for fascial herniation or muscle fiber herniation through fascial defects. The key distinguishing feature—appearing and disappearing at random—is atypical for classic lipomas but can occur with small fascial hernias that reduce spontaneously.

Diagnostic Approach

Initial Clinical Assessment

• Document the exact anatomic location, size (3cm each), and orientation (horizontal parallel lines) of the lesions 1
• Examine during Valsalva maneuver or with muscle contraction to determine if the lumps become more prominent (suggesting fascial herniation) or remain unchanged (favoring lipoma) 2
• Palpate for consistency: soft, compressible masses favor lipoma; firm, reducible masses suggest herniation 3
• Check for the "pillow sign": gentle pressure causing indentation is highly specific (98%) for lipomatous lesions 3

First-Line Imaging

Ultrasound is the definitive first-line imaging modality for this presentation 4, 3. This provides:

• Sensitivity of 86.87-94.1% and specificity of 95.95-99.7% for lipomas 4
• Characteristic features to confirm lipoma: well-circumscribed, hyperechoic or isoechoic appearance compared to surrounding fat, thin curved echogenic lines within the mass, minimal to no internal vascularity on Doppler, and no acoustic shadowing 4, 3
• Ability to identify fascial defects if herniation is present 2

When to Pursue Advanced Imaging

MRI is indicated only if ultrasound shows atypical features 4:

• Size larger than 5 cm 4
• Deep-seated location (though this case is superficial) 4
• Rapid growth or pain 4
• Atypical ultrasound characteristics suggesting possible atypical lipomatous tumor 4

Management Strategy

For Asymptomatic, Typical Lipomas

Observation is appropriate when ultrasound confirms classic lipoma features and the patient has no symptoms 3. The transient nature may represent:

• Small lipomas that shift position with body movement
• Intermittent fascial herniation of subcutaneous fat
• Muscle fiber herniation through small fascial defects

Indications for Intervention

Surgical excision is recommended if 3:

• Symptoms develop (pain, bleeding, functional impairment)
• Diagnostic uncertainty persists after imaging
• Patient preference for removal
• Lesions demonstrate growth on follow-up

Critical Pitfalls to Avoid

• Do not assume benignity based on clinical examination alone: physical examination correctly identifies only 85% of lipomas 3
• Do not dismiss the transient nature as insignificant: this may indicate fascial herniation requiring different management than simple lipoma 2
• Do not perform plain radiographs first: they identify intrinsic fat in only 11% of soft tissue masses and are unrewarding for small superficial lesions 4, 3
• Do not biopsy without imaging confirmation: ultrasound should precede any invasive procedure to characterize the lesion and guide management 4

Differential Considerations

While linear lesions can follow Blaschko's lines (representing developmental patterns) 1, 5, the description of "lumps" rather than pigmentary or inflammatory changes, combined with the transient nature and location in the iliac fossa, makes this less likely. Linear dermatoses along Blaschko's lines typically present with visible skin changes (pigmentation, inflammation, or textural changes) rather than palpable subcutaneous masses 1, 5.

The age (24 years), location (left iliac fossa), and transient nature strongly favor either lipomatosis or fascial herniation over inflammatory dermatoses or vascular lesions 1.