Skull X-ray Findings in Multiple Myeloma
The characteristic skull X-ray finding in multiple myeloma is multiple "punched-out" osteolytic lesions—well-defined, round radiolucent defects without sclerotic borders, often described as having a "raindrop" or "Swiss cheese" appearance. 1
Classic Radiographic Features
The hallmark skull findings include:
- Discrete, round, sharply demarcated areas of bone destruction without any surrounding reactive bone formation or sclerotic rim 1
- Multiple well-circumscribed lytic lesions with diffuse osteopenia throughout the calvarium 2
- These lesions only become visible on X-ray after more than 50% of trabecular bone has been lost, meaning early disease may appear normal 1
Diagnostic Role and Limitations
A complete skeletal survey including skull X-rays remains part of the standard diagnostic workup and is incorporated into the CRAB criteria (hypercalcemia, renal insufficiency, anemia, bone lesions) used to define symptomatic myeloma requiring treatment 3, 1
However, important limitations exist:
- Conventional X-rays miss significant bone disease due to the 50% bone loss threshold required for visualization 1
- Whole-body low-dose CT (WBLD-CT) detects up to 60% more relevant findings compared to conventional skeletal surveys and is now recommended as the novel standard procedure 1, 4
- Despite CT superiority overall, skull and rib lesions are actually not as well detected by WBLD-CT or MRI compared to conventional skeletal surveys, so focused skull X-rays retain value when these areas are of clinical concern 1, 4
Detection Rates Across Imaging Modalities
Research demonstrates high detection rates for skull involvement:
- Lateral skull radiographs detected punched-out lesions in 93% of patients, frontal skull views in 91%, and panoramic jaw radiographs in 87% 5
- Skull and jawbone lesions occur synchronously in 83% of cases 5
- FDG-PET/CT achieves 90% sensitivity for detecting focal lesions greater than 5 mm 1
Management Approach
When skull lesions are identified on X-ray, this confirms symptomatic multiple myeloma requiring systemic treatment per diagnostic criteria 3:
- Diagnosis requires ≥10% clonal plasma cells on bone marrow examination AND evidence of end-organ damage (CRAB criteria) 3
- The presence of lytic bone lesions fulfills the "B" component of CRAB criteria 3
For ongoing monitoring during treatment, WBLD-CT should be performed as the primary imaging modality at minimum every 3 months during active treatment 4
Clinical Pitfalls to Avoid
- Do not rely solely on normal skull X-rays to exclude myeloma bone disease—early lesions are radiographically occult 1
- While sclerotic lesions are rare (only 3% of cases), they can occur and should not exclude the diagnosis 6
- When solitary osteolytic skull lesions are present, always consider plasmacytoma or multiple myeloma in the differential diagnosis and perform bone marrow studies 7
- Combine imaging with laboratory monitoring including serum/urine M-protein and serum free light chains for comprehensive disease assessment 4