Cockade Sign | Radiology Signs

Answer:

The Cockade sign represents the characteristic radiological appearance of a benign intraosseous lipoma, most classically seen in the calcaneus (heel bone). This rare, slow-growing benign tumor of the bone is composed primarily of mature adipose (fat) tissue. On plain radiographs, it appears as a well-circumscribed, radiolucent (lytic) lesion with a distinct central area of calcification or ossification. On CT imaging or MRI, the peripheral portion of the lesion will demonstrate fat attenuation or signal intensity, confirming the diagnosis, while the central focus appears as dense calcification. Most intraosseous lipomas are asymptomatic and discovered incidentally.

Why is it called so?

The sign is named the Cockade sign because the lesion’s appearance—a distinct dense center surrounded by a radiolucent halo—strikingly resembles a “cockade” (a circular rosette or knot of ribbons historically worn on a hat as a badge) or a bullseye target.

Pathophysiology

Intraosseous lipomas arise from the proliferation of mature adipocytes within the medullary cavity of the bone. Over time, the lesion undergoes central involution and ischemic necrosis due to poor blood supply. The infarcted central fat saponifies and subsequently undergoes dystrophic calcification or ossification. It is this central necrotic calcification, surrounded by the remaining radiolucent viable fat in the bone marrow cavity, that creates the classic target-like or cockade appearance on imaging.

Alternative names:
Target sign (of intraosseous lipoma)

Other associated signs:
Cockade sign (ultrasound) is a completely different sign used in abdominal imaging to describe the target-like appearance of thickened bowel or gastric walls (seen in conditions like appendicitis, pyloric stenosis, or GI tumors).