Fibrous Dysplasia

Question 1

Give a brief definition of fibrous dysplasia

Answer 1

A focal, slow expanding bone lesion in which bone is replaced by a mass of: Fibroblasts, randomly distributed collagen fibres and islands of woven bone trabeculae

Question 2

Distinguish between monostotic and polyostotic fibrous dysplasia

Answer 2

Mono
-	~70% of cases
-	Affects males and females equally
-	Usually occurs in childhood, but may affect any age
Features:
-	Only affects one bone
-	Usually asymptomatic
-	May observe: Bone enlargement, pain due to pathological fractures or pressure on nerves

Poly
-	25% of cases
-	Affects males and females equally
-	Usually appears at earlier age than monostotic disease
Features:
-	Affects multiple bones
-	May be uni or bilateral
-	Shoulder and pelvic girdles often severely affected
-	Multiple skeletal deformities observed
-	Pain due to pathological fractures

Question 3

Describe the typical bony lesion in fibrous dysplasia

Answer 3

• Tends to be unilateral
• Shoulder and pelvic girdles usually affected
• Histologically: Increased osteoclast and fibroblast numbers, scattered trabeculae of irregular woven bone

Question 4

Discuss the radiological diagnosis of fibrous dysplasia

Answer 4

• Well circumscribed, minimally expansive (“geographic”) lytic lesions – severity varies depending on ratio of fibrous/osseous tissue)
• Ground-glass/frosted appearance (uniformly opaque) – due to absence of trabeculae
• Diaphyseal or diametaphyseal location