Sunburst

The rays of the sun are seen spreading around its bright center,

an appearance described as a sunburst 

A similar appearance can be described in bone radiographs of individuals with

Periosteal Osteosarcoma, a type of bone cancer.

          Periosteal Osteosarcoma is a subtype of Osteosarcoma, a malignant tumor of the bones. It commonly occurs in the long bones of the extremities near the metaphyseal growth plates. The most common sites are the femur (max%), the tibia (mostly proximal tibia), and the humerus.

The tumor arises from the inner layer of the periosteum. It elevates the periosteum and produces a periosteal reaction.

Periosteal reaction means reactive bone formation i.e., the periosteum produces new bone in response to certain stressful stimuli such as breaks, tears, stretches, inflammation or irritants. The pattern of periosteal reaction varies depending on the stimulus. The visualisation of this pattern in radiographic images aids the identification and differentiation of malignant and benign tumors.

In Osteosarcoma, the tumor grows rapidly but steadily due to which the periosteum does not have enough time to lay down even a thin layer of bone. Instead, the tiny fibers that connect the periosteum to the bone (Sharpey’s fibers) become stretched out perpendicular to the bone. When these fibers ossify, they produce a pattern visible on radiographic images as “sunburst” or “hair-on-end” periosteal reaction.

 Thus, in Osteosarcoma, the periosteal reaction which is a spiculated pattern of calcification that is oriented perpendicular to the bone, gives it the hair on end or sunburst appearance.

Links to radiographic images of Sunburst appearance in Osteosarcoma:

X-ray image of Osteosarcoma

Osteosarcoma of the Fibula 

Sunburst appearance & Codman triangle seen in Osteosarcoma

      Links to some basic facts:

      Parts of the bone 

       Layers of the bone

       Layers of the periosteum

       Periosteal reactions in other bone conditions

       What is Codman triangle?

Radiographic findings in Periosteal Osteosarcoma:

·       *Broad based surface soft tissue mass(tumor)

·   *Extrinsic erosion of thickened diaphyseal cortex by the tumor

·   *Concaving (or) endosteal scalloping of the diaphyseal cortex due to invasion by the tumor

·   *Periosteal reaction which invades into the soft tissue component.

·   *Periosteal reaction predominantly perpendicular to the diaphyseal cortex.

     *Maturity and extent of mineralization in to soft tissue mass (mild, moderate, marked).     

  

References:

Periosteal Osteosarcoma_tumorsurgery.org 

Periosteal reaction_rad.washington.edu 

Periosteal Osteosarcoma_A review of clinical evidence

Periosteal reaction_radiopaedia.org

All about Periosteal reaction_pdf_ajronline.org