Polka Dot sign | Radiology Signs

Answer:
The Polka Dot sign is caused by vertebral hemangiomas, benign vascular tumors within the vertebral body. These lesions feature vascular proliferation and fatty marrow replacement, alongside thickened vertical trabeculae that appear as multiple small, rounded sclerotic dots on axial imaging with CT or MRI. Clinically, typical vertebral hemangiomas are often asymptomatic, but aggressive variants can present with neurological symptoms due to spinal cord or nerve root compression.

Why is it called so?

The name “Polka Dot sign” describes the imaging appearance of thickened vertical trabeculae seen in cross-section on axial scans, which look like multiple small, discrete dots arranged in a pattern reminiscent of polka dots.

Pathophysiology

The sign develops as the normal cancellous bone within the vertebral body is replaced by a network of dilated venous channels (vascular proliferation) and fat. This process causes thickening and sclerosis of the vertical trabeculae. On axial imaging, the cross-sectional view of these thickened trabeculae appears as multiple small dots surrounded by lucent areas formed by the vascular spaces and fat, producing the characteristic polka dot pattern.

Alternative names: None. (“Salt and pepper sign” is sometimes loosely applied but is imprecise for this entity, as that term is more properly used for unrelated findings such as the skull in hyperparathyroidism or paraganglioma on MRI.)

Other associated named signs: Corduroy sign and jail bar sign (both describe the same vertically thickened trabeculae seen on sagittal/coronal imaging)

References

1. Persaud T. The polka-dot sign. Radiology. 2008.