What is the best initial imaging test to order for an adult patient presenting with a movable scalp lump?

Movable Scalp Lump: Initial Imaging Recommendation

For a movable scalp lump in an adult, order MRI with IV contrast as the primary imaging test, as it provides superior soft tissue characterization and anatomic detail for distinguishing benign from malignant lesions. 1

Risk Stratification Before Imaging

Before ordering any imaging, assess malignancy risk based on these specific criteria:

Duration and behavior:

• Mass present ≥2 weeks without significant fluctuation 1
• Mass of uncertain duration 1

Physical examination red flags:

• Fixation to adjacent tissues 1
• Firm consistency 1
• Size >1.5 cm 1
• Ulceration of overlying skin 1

Patient history factors:

• Lack of infectious etiology 1
• Prior malignancy history 1
• Smoking history 1

Imaging Selection Algorithm

For patients at increased risk for malignancy:

Primary choice: MRI with IV contrast 1

• Provides superior soft tissue contrast and anatomic detail compared to CT 1
• Critical for characterizing the mass, delineating borders, and identifying potential intracranial extension 1
• Requires post-contrast T1-weighted sequences in multiple planes (axial, sagittal, coronal) 1

Alternative: CT with IV contrast 1

• Use only if MRI is contraindicated (claustrophobia, pacemakers, severe renal insufficiency) 1
• Provides adequate characterization but less soft tissue detail than MRI 2

For low-risk patients with clearly benign features:

Consider ultrasound as initial screening 3

• Appropriate for superficial, mobile, cystic-appearing lesions 3
• Over 50% of benign scalp lesions are cystic (trichilemmal cysts, epidermoid cysts, dermoid cysts, lipomas) 4
• Requires experienced operator for accurate interpretation 5
• If ultrasound findings are indeterminate, proceed to MRI with contrast 3

Critical Ordering Details

When ordering imaging, specify:

• Anatomical location (scalp) 1
• Clinical indication (movable scalp mass, duration, risk factors) 1
• "With IV contrast" unless contraindicated by severe renal insufficiency or contrast allergy 1
• Risk factors present (if any) 1

Common Pitfalls to Avoid

Do not order CT without and with contrast 1

• This doubles radiation exposure with minimal diagnostic benefit 1

Do not omit contrast unless specifically contraindicated 1

• Non-contrast studies provide significantly less diagnostic information for characterizing masses 1

Do not delay imaging with empiric antibiotics 1

• Only prescribe antibiotics if clear signs of bacterial infection exist (warmth, erythema, fever, tenderness) 1
• Empiric antibiotics without infection delay cancer diagnosis and worsen outcomes 6

Do not assume cystic masses are benign 6

• Up to 80% of cystic neck masses in patients over 40 are malignant 6
• Continue evaluation until definitive diagnosis is obtained 2

When to Consider Additional Imaging

If the scalp mass is deemed at increased risk for malignancy after initial imaging:

• Consider chest CT to evaluate for distant metastases or primary lung cancer in heavy smokers 6
• FDG-PET/CT is reserved for staging after malignancy is diagnosed, not for initial evaluation 2