70.如圖所示顎骨病變中黑色箭頭及白色箭頭所指之放射線不透過性（radiopaque）影像，最有可能分別為下列 何者？
(A)fractured alveolar crest and fractured cortical bone
(B)sequestra and periosteal reaction
(C)tumor mass and cortical invasion
(D)fractured alveolar crest and hyoid bone

These are two classic radiographic signs seen in osteomyelitis and other bone diseases.

1. Sequestrum (plural: Sequestra)

What is it?

A piece of dead bone that has lost its blood supply and becomes separated from the surrounding living bone.

How does it form?

Infection → inflammation → blood vessels compressed/thrombosed → bone necrosis → dead bone fragment remains.

X-ray appearance

• Radiopaque (white) fragment

• Surrounded by a radiolucent (dark) area of bone destruction

Think:

Sequestrum = dead bone trapped inside infected bone

Mnemonic:
Sequestrum = "Separated dead bone"

2. Periosteal Reaction

What is it?

The periosteum (the membrane covering bone) responds to irritation by producing new bone.

Causes

• Infection (osteomyelitis)

• Trauma

• Tumors

• Inflammation

X-ray appearance

New layers of bone deposited on the bone surface.

Patterns include:

Think:

Periosteal reaction = living bone trying to protect itself by laying down new bone

Easy Comparison

Exam Pearl

In chronic osteomyelitis you may see both:

• Sequestrum → dead bone fragment

• Periosteal reaction → new bone laid down around infection

So the bone is simultaneously:

dying on the inside (sequestrum) and trying to heal on the outside (periosteal reaction).