What causes the Sunburst sign in the skull on plain radiography and CT imaging?
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Answer:
The Sunburst sign represents a characteristic radiological appearance of benign intraosseous hemangiomas affecting the skull vault, particularly the frontal and parietal bones. These are slow-growing vascular lesions composed of abnormal disorganized proliferation of vascular channels interspersed with fat. The lesion appears as an expansile bone lesion with thin borders and a distinctive pattern of radiating trabecular thickening emanating from a common central point. On CT imaging, this trabecular pattern is more clearly delineated and shows radiating spicules of bony trabeculae. Plain radiographs typically demonstrate a lytic lesion with a sclerotic rim. While most calvarial hemangiomas remain asymptomatic and are incidental findings, some patients may present with cosmetic deformity, headache, or less commonly neurological symptoms. These benign lesions may erode both the inner and outer tables of the skull with potential for internal or external expansion.
Why is it called so?
The sign is named the Sunburst sign due to its visual resemblance to rays of sunlight radiating outward from the sun. The radiating pattern of trabecular thickening projecting from a central epicenter mimics this astronomical phenomenon, creating a distinctive radiating spiculated appearance on imaging.
Pathophysiology
Skull hemangiomas develop as hamartomatous vascular tissue proliferations within the diploic space of the calvarium. The radiating trabecular pattern results from reactive bone formation and remodeling around the expanding vascular lesion. As the hemangioma grows, it stimulates osteoblastic activity and trabecular hypertrophy, creating linear bony septa that radiate centrifugally from the lesion’s center. This organized bone response to the expanding vascular mass produces the characteristic radiating architecture visible on imaging.
Alternative names:
Sunray sign, Honeycomb appearance (when the pattern demonstrates central lucency with surrounding trabecular thickening).
Other associated named signs:
Dural tail sign may be present on contrast-enhanced MRI when the lesion grows along the inner surface of the skull, though dural invasion does not occur.
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