What are the possible causes, recommended evaluation, and management for a palpable lump in the flexural crease of the arm?

Evaluation and Management of Lumps in Arm Creases

For a palpable lump in the flexural crease of the arm, start with plain radiographs as the initial imaging study, followed by ultrasound for superficial masses or MRI for deep/atypical lesions, with the primary goal of distinguishing benign from malignant pathology before proceeding to excision. 1

Initial Imaging Approach

The ACR Appropriateness Criteria establishes a clear algorithmic pathway 1:

First-Line: Plain Radiographs

• Always obtain radiographs first to identify mineralization, ossification patterns, and bone involvement
• Radiographs detect calcification that may suggest specific diagnoses (myositis ossificans, vascular malformations)
• They identify any underlying bone pathology or cortical changes

Second-Line: Ultrasound for Superficial Masses

If the lump is palpable in the subcutaneous tissue:

• Ultrasound has 94.1% sensitivity and 99.7% specificity for superficial masses 1
• Most accurate for: lipomas > vascular malformations > epidermoid cysts > nerve sheath tumors
• Confirms solid vs. cystic nature
• Identifies relationship to neurovascular structures

Critical caveat: 96% of superficial masses are benign, but atypical US features mandate further imaging 1

When to Escalate to MRI

Proceed to MRI if:

• Mass is deep to fascia (ultrasound accuracy drops precipitously for deep lesions) 1
• Clinical or ultrasound features are atypical
• Located in anatomically complex areas
• Size >5 cm (giant lipomas in the arm average 7 cm and require MRI evaluation) 2

Specific Considerations for Arm Crease Location

Deep-seated lipomas are the most common pathology in this location 2:

• Seven of 13 deep lipomas in one series occurred in the arm
• Can be intramuscular, intermuscular, or parosteal (attached to bone)
• Mean size 7 cm at presentation
• May cause nerve compression (radial paralysis reported)

Key differentiating features:

• Progressive, slow-growing mass = likely benign lipoma
• Associated neurologic symptoms = requires urgent evaluation for nerve compression
• Rapid growth or firm consistency = raises concern for malignancy

Management Algorithm

1. Clinical assessment: Document size, consistency, mobility, associated symptoms (pain, paresthesias, weakness)

2. Imaging sequence: Radiographs → Ultrasound (if superficial) OR MRI (if deep/atypical)

3. Excision indications:

   • All soft tissue masses should be excised with histopathologic examination because clinical determination of benign vs. malignant is unreliable 3
   • Marginal excision is treatment of choice for confirmed lipomas 2
   • Excise with safety margin given difficulty distinguishing benign from malignant clinically

4. Prognosis: Deep-seated lipomas of the upper extremity have excellent prognosis regardless of size, unlike lower extremity or retroperitoneal lipomas 2

Common Pitfalls to Avoid

• Do not skip radiographs: CT and MRI cannot adequately identify mineralization patterns that radiographs detect 1
• Do not rely solely on ultrasound for deep masses: Accuracy drops significantly below the fascia 1
• Do not use MRI as initial study: Not supported by literature and misses mineralization 1
• Do not assume giant size indicates malignancy in upper extremity lipomas—prognosis remains good 2