Skull Findings on X-ray in Multiple Myeloma
The characteristic skull finding on X-ray in multiple myeloma is the presence of multiple "punched-out" osteolytic lesions, which appear as well-defined, round radiolucent defects without sclerotic borders, often described as having a "raindrop" or "Swiss cheese" appearance. 1
Classic Radiographic Appearance
- Osteolytic lesions are the hallmark finding, appearing as discrete, round, sharply demarcated areas of bone destruction without surrounding reactive bone formation 1
- These lesions result from increased osteoclastic activity that is not accompanied by compensatory osteoblastic bone formation 2, 3
- The skull is a common site for these lesions, though they can be present throughout the skeletal system 4
Imaging Characteristics and Limitations
- Conventional skeletal survey (including skull X-rays) remains the standard technique for detecting lytic lesions and is used in the CRAB criteria (hypercalcemia, renal insufficiency, anemia, bone lesions) for defining myeloma-requiring treatment 1
- However, radiographic detection has significant limitations—lytic lesions only become visible on X-ray after more than 50% of trabecular bone has been lost 1
- Skull lesions may be asymptomatic or can grow externally, and rarely there is intracranial expansion 4
Advanced Imaging Considerations
While conventional X-rays remain standard, newer modalities offer superior detection:
- 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 for diagnosis of lytic disease 1, 5
- FDG-PET/CT has 90% sensitivity for detecting various myeloma lesions including focal lesions greater than 5 mm 1
- However, skull and rib lesions are 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 5
Clinical Implications
- The presence of lytic bone lesions on skeletal survey is part of the diagnostic criteria for symptomatic multiple myeloma requiring treatment 1
- Skull myeloma involvement can affect cranial nerves, with cranial nerves II, V, VI, VII, and VIII being most commonly affected 4
- Multiple vertebral and skull involvement with osteolytic changes is typical, though solitary lesions can occur 4