What is the diagnostic approach for a fatty mass at the elbow?

Diagnostic Approach for a Fatty Mass at the Elbow

For a suspected fatty mass at the elbow, begin with plain radiographs as the initial imaging study, followed by MRI without contrast if the mass characteristics remain unclear or if deeper tissue characterization is needed. 1

Initial Imaging: Radiographs

Radiographs should be obtained first for any elbow soft tissue mass, as they provide critical baseline information and may be diagnostic in many cases 1:

• Radiographs identify intrinsic fat within masses in 11% of cases and can be diagnostic for lipomas when characteristic lucency is present 1
• They exclude underlying bone involvement (present in 22% of soft tissue masses) and detect calcifications (found in 27% of cases) 1
• Radiographs may reveal unsuspected skeletal abnormalities manifesting as soft tissue masses 1

Key limitation: Radiographs may be unrewarding when masses are small, deep-seated, non-mineralized, or in areas with complex anatomy 1

Advanced Imaging: When Radiographs Are Nondiagnostic

For Superficial Masses (Above Deep Fascia)

Ultrasound is the preferred next step for superficial or subcutaneous suspected lipomas 1:

• US demonstrates 94.1% sensitivity and 99.7% specificity for superficial soft tissue masses, with highest accuracy for lipomas 1
• Characteristic lipoma features include minimal acoustic shadowing, minimal vascularity, and simple curved echogenic lines within an encapsulated mass 1
• Critical caveat: When US or clinical features are atypical, MRI is mandatory for further characterization 1

For Deep or Nonspecific Masses

MRI without contrast is the definitive imaging modality for deep elbow masses or when superficial mass characteristics are atypical 1:

• MRI provides comprehensive soft tissue characterization and relationship to neurovascular structures 1
• Important limitation: MRI has inherent limitations in identifying mineralization and should not be used in isolation without initial radiographs 1

Imaging Modalities NOT Recommended

• CT: Not typically ordered for initial soft tissue mass evaluation 1
• FDG-PET/CT: Not appropriate for initial soft tissue mass assessment 1
• MRI as first-line: Literature does not support MRI as the initial examination without preceding radiographs 1

Clinical Algorithm

1. Always start with radiographs (anteroposterior and lateral views) 1
2. If superficial and clinically consistent with lipoma → Ultrasound for confirmation 1
3. If deep, atypical features, or US inconclusive → MRI without contrast 1
4. If mineralization or bone involvement suspected → CT may be added after radiographs 1

Common Pitfalls to Avoid

• Never skip radiographs: Despite being considered "unrewarding" by some, radiographs show positive findings in 62% of soft tissue masses 1
• Don't rely solely on physical examination: Only 85% of lipomas are correctly identified by physical examination alone 1
• Recognize US limitations: US cannot adequately assess deep masses or those in anatomically complex regions like the elbow 1