Lump Under Clavicle Appearing Only with Chest Protrusion
This is most likely a normal anatomical prominence of the sternoclavicular joint (SCJ) or medial clavicle that becomes visible with postural changes, though benign conditions like SCJ subluxation, osteoarthritis, or condensing osteitis should be considered if there is actual enlargement.
Understanding the Clinical Presentation
The key feature here is that the lump appears only when protruding the chest, which strongly suggests a positional or anatomical variant rather than a true pathological mass. When you stick your chest out, the sternoclavicular joint and medial clavicle naturally become more prominent due to:
- Normal anatomical variation - The medial clavicle and SCJ can be more prominent in some individuals, particularly those who are thin or have less overlying soft tissue 1
- Positional subluxation - The SCJ can subluxate anteriorly with certain chest positions, creating a visible prominence that reduces when relaxed 2
Differential Diagnosis for True Medial Clavicular Enlargement
If there is actual enlargement (not just positional prominence), the most common benign causes include 2:
- Osteoarthritis of the sternoclavicular joint - Common in older adults, typically asymptomatic 2
- Condensing osteitis - Benign sclerotic condition of the medial clavicle 2
- Spontaneous SCJ dislocation - Can occur atraumatically and may be positional 2
- Sternocostoclavicular hyperostosis - Inflammatory condition causing medial clavicle enlargement 2
Critical Red Flags Requiring Further Evaluation
Ultrasound should be the first-line imaging modality for any superficial chest wall mass that persists or raises concern 3. Proceed with imaging if:
- The lump is persistently present (not just positional) 3
- There is associated pain, tenderness, or functional limitation 1
- Rapid growth or change in characteristics 3
- History of trauma without resolution 4
- Systemic symptoms (fever, weight loss, night sweats) suggesting infection or malignancy 3
- Age >35 years with smoking history - increases concern for malignancy 3
Recommended Diagnostic Approach
Initial Assessment
- Observe the lump in both relaxed and chest-protruded positions - if it completely disappears when relaxed, this strongly favors normal anatomy 1
- Palpate for true bony enlargement versus soft tissue prominence 2
- Assess for tenderness, warmth, or overlying skin changes 1
- Document any history of trauma, repetitive overhead activities, or weight training 4, 5
When to Image
If the lump persists when relaxed or there are concerning features:
- Ultrasound first - excellent for visualizing SCJ anatomy, soft tissue masses, and distinguishing bony from soft tissue pathology 3, 1
- Plain radiographs - can identify clavicle fractures, osteoarthritis, or bony lesions if trauma history exists 4, 2
- CT chest - reserved for suspected deeper involvement, chest wall invasion, or when ultrasound is inconclusive 3
Biopsy Considerations
Image-guided biopsy is only indicated if:
- Imaging reveals a true mass with concerning features (irregular margins, rapid growth, invasion) 3
- Malignancy risk factors are present and diagnosis remains uncertain 3
Common Pitfalls to Avoid
- Don't assume all positional prominences are pathological - many are normal anatomical variants that become visible with postural changes 1
- Don't overlook trauma history - even minor falls can cause clavicle fractures that present as lumps, especially in young adults 4
- Don't forget that in patients <35 years without trauma or systemic symptoms, malignancy is extremely rare 3, 6
- Don't order advanced imaging for clearly positional, asymptomatic prominences - clinical observation is sufficient 2
Management for Benign Positional Findings
If examination confirms the lump is purely positional (disappears completely when relaxed) and there are no red flags: