Characteristic Skull X-ray Findings in Multiple Myeloma
The classic skull X-ray finding in multiple myeloma shows multiple "punched-out" osteolytic lesions—well-defined, round radiolucent defects without sclerotic borders, often described as having a "raindrop" or "Swiss cheese" appearance. 1
Radiographic Appearance
The hallmark skull findings include:
- Discrete, round, sharply demarcated areas of bone destruction without surrounding reactive bone formation or sclerotic margins 1
- Multiple osteolytic lesions that appear as radiolucent (dark) defects scattered throughout the calvarium 1, 2
- The "punched-out" appearance reflects the underlying pathophysiology of increased osteoclastic activity with suppressed osteoblastic function 3
Important Diagnostic Limitations
Conventional skull X-rays have significant sensitivity limitations:
- Lytic lesions only become visible on X-ray after more than 50% of trabecular bone has been lost, meaning early disease may be missed 1
- Despite this limitation, skeletal survey including skull films remains part of the standard CRAB criteria (hypercalcemia, renal insufficiency, anemia, bone lesions) used to diagnose symptomatic multiple myeloma requiring treatment 3
Role in Diagnostic Workup
A complete skeletal bone survey including skull, spine, pelvis, humeri and femurs is necessary for initial evaluation 3:
- Skull X-rays are specifically included as part of the comprehensive radiological assessment 3
- The presence of lytic bone lesions on skeletal survey contributes to meeting diagnostic criteria for symptomatic multiple myeloma 1, 4, 5
Modern Imaging Considerations
While skull X-rays show the classic findings, whole-body low-dose CT (WBLD-CT) is now the recommended standard procedure for detecting lytic disease 3, 1:
- WBLD-CT detects up to 60% more relevant findings compared to conventional skeletal surveys 1, 6
- However, 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 may still be valuable when these areas are of clinical concern 1, 6
Clinical Context
When skull lesions are identified:
- They represent part of the "B" (bone lesions) component of CRAB criteria defining symptomatic disease 3, 4, 7
- Multiple osteolytic skull lesions in conjunction with ≥10% clonal bone marrow plasma cells confirm the diagnosis of symptomatic multiple myeloma requiring treatment 3, 4, 7
- Systemic bone scanning typically reveals additional osteolytic lesions in other skeletal sites 2