What is the cause of a hard mass on the medial clavicle in a patient with normal X-ray, Computed Tomography (CT) scan of the head, neck, and chest, and ultrasound results?

Differential Diagnosis of Hard Medial Clavicular Mass with Normal Imaging

The most likely diagnosis is condensing osteitis of the clavicle, a benign idiopathic condition that typically presents as a palpable hard mass over the medial clavicle in women of late child-bearing age, with characteristic radiographic sclerosis that may be subtle or missed on initial imaging. 1

Primary Diagnostic Considerations

Condensing Osteitis (Most Likely)

• This benign degenerative or mechanical condition characteristically presents as a variably painful and tender swelling over the medial end of the clavicle 1
• Radiographs show sclerosis and slight expansion of the medial one-third of the clavicle, though these findings can be subtle 1
• Predominantly affects women of late child-bearing age 1
• The discrepancy between palpable findings and "normal" imaging may reflect subtle sclerotic changes that were not appreciated on initial review 1

Other Differential Diagnoses to Consider

Malignant lesions must be excluded despite normal imaging:

• Primary bone tumors (chondrosarcoma, giant cell tumor) can present as palpable masses and require tissue diagnosis 2, 3
• Chondrosarcoma of the clavicle presents as a palpable mass in 69% of cases 3
• Metastatic disease to the clavicle (particularly from thyroid cancer) can cause osteolysis and present as a hard mass 4

Fracture-related pathology:

• Periarticular medial clavicle fractures can present with displaced fragments creating a palpable mass 5
• CT is superior to plain radiography for detecting these fractures 5

Recommended Diagnostic Algorithm

Immediate Next Steps

1. Re-review existing imaging with specific attention to:

   • Subtle sclerosis or expansion of the medial clavicle on X-ray and CT 1
   • Bone density changes that may have been initially overlooked 1
   • Any cortical disruption or periosteal reaction 5

2. Obtain MRI of the clavicle if not already performed:

   • MRI provides superior soft tissue contrast and can detect marrow abnormalities not visible on CT 6
   • Can assess for invasion across tissue planes and involvement of neurovascular structures 6

3. Perform biopsy for definitive diagnosis:

   • Incisional or excisional biopsy is recommended unless pain is insignificant and clinical presentation strongly supports condensing osteitis 1
   • Fine-needle aspiration with cytology can achieve correct diagnosis in 94% of cases at dedicated centers 3
   • Biopsy is essential to exclude malignancy, as numerous expensive screening tests are not recommended without tissue diagnosis 1

Management Based on Diagnosis

If Condensing Osteitis Confirmed:

• Patients with slight pain often need no treatment 1
• Anti-inflammatory medications are variably effective 1
• Excision of the medial one-third of the clavicle is indicated for refractory cases 1

If Malignancy Identified:

• Surgical resection is the treatment of choice for primary chondrosarcoma and other clavicular tumors 3
• Wide local excision with reconstruction (autogenous fibula graft) for giant cell tumors 2
• Composite resection including segmental osteotomy for metastatic disease 4

Critical Pitfalls to Avoid

• Do not dismiss a palpable hard mass simply because initial imaging appears "normal"—subtle sclerotic changes in condensing osteitis can be easily missed 1
• Do not order extensive screening tests for presumed metastatic disease before obtaining tissue diagnosis 1
• Do not delay biopsy when malignancy cannot be confidently excluded clinically and radiographically 1, 3
• Re-review imaging with a musculoskeletal radiologist if there is clinical-radiological discordance 1