Fibrous Dysplasia

Question 1

Fibrous Dysplasia Definition

Answer 1

• A benign focal slowly expanding lesion in which bone is slowly replaced by a mass of fibroblasts, collagen and irregular bony trebeculae of woven bone.
• Is a focus of disordered maturation of bone with arrest at the immature stage of woven bone.

Question 2

Fibrous Dysplasia Definition 2

Answer 2

FD is a focal, slowly expanding bone lesion in which bone is replaced by a mass of:
•Fibroblasts
•Randomly distributed collagen fibres
•Islands of woven bone trabeculae

Question 3

Fibrous Dysplasia Definition 3

Answer 3

• Disturbance of spongy bone maintenance in which bone undergoing physiologic lysis (ie mineral release/remodelling) is replaced by an abnormal proliferation of fibrous tissue
• This results in asymmetric distortion and expansion of bone

Question 4

Fibrous dysplasia Classifications:

Answer 4

• Monostotic
• Polyostotic
• McCune-Albright syndrome

Question 5

Monostotic FD:

Answer 5

• 70% of cases
• Affects both ♂& ♀
• Usually occurs in childhood
• May occur at any age (but usually begins in childhood with progression often stopping its progress at puberty)

Question 6

Monostotic FD Bones:

Answer 6

NOTE: Monostotic FD is the most common benign lesion of the rib cage
•Femur
•Tibia
•Maxilla
•Mandbile

Question 7

Monostotic FD Etiology:

Answer 7

•Somatic mutation in the Glutamine Synthetase gene.
•The mutation is believed to occur post fertilization, which accounts for the mosaic distribution of abnormal cells
The effects of the mutation include:
•↑ed osteoclast numbers (bone resorption)
•↑ed fibroblast numbers

•DOES NOT PROGRESS TO POLYSTOTIC FORM

Question 8

Pathological picture of ALL FD:

Answer 8

Affected bone is replaced by:
•Proliferating fibroblasts
•Scattered trabeculae of irregular woven bone
•The usual rim of osteoblasts around the bony trabeculae is absent
Note: this pathological picture is the same for all forms of FD

Question 9

Monostotic FD lesion may cause:

Answer 9

May observe:
•Tumorous distortion of bone
•Disfigurement of face/skull
•Pain

Question 10

Polystotic FD:

Answer 10

• 25% of cases
• Affects ♂& ♀ equally
• Usually appears at an earlier age than monostotic disease and may progress until middle age

Question 11

Polystotic FD Bone Involvement:

Answer 11

Can be:
•unilateral
•bilateral

Question 12

Polystotic FD Bone Involvement:

Answer 12

Bones: 
 •Femur (most common)
 •Skull 
 •Tibia 
 •Humerus 
 •Ribs etc
 •Craniofacial bones 

•The shoulder and pelvic girdles are often severely affected

• Multiple skeletal deformities seen
• Pain due to fractures: there is a marked predisposition to pathological fractures

Question 13

Polystotic FD Craniofascial bones affected:

Answer 13

• 50% of patients with moderate dissemination

* 100% of patients with extensive disease

Question 14

McCune – Albright Syndrome

Answer 14

• 5% of FD cases
• Polystotic FD with:
  
  • Multiple unilateral bone lesions
  • Unilateral pigmented skin lesions
  • Skin lesion on the same side as bone lesions
  • Autonomous endocrine hyperfunction

Question 15

Autonomous endocrine hyperfunction in McCune-Albright syndrome:

Answer 15

• precocious sexual development
• Hyperthyroidism
• Cushing’s Syndrome
• Acromegaly
• Most COMMON endocrine abnormality is precocious sexual development F>M

Question 16

McCune-Albright Syndrome Clinical manifestations:

Answer 16

Skin lesion description:
   •Large macules
   •Cafe-au-lait to dark brown
   •Irregular serpigenous border
   •Found manly on:
       –Neck, chest, back shoulder, and pelvic region

Question 17

McCune-Albright Clinical Course

Answer 17

• Unpredicatable course

* Early the onset the more progressive

Question 18

Clinical Course of Monostotic FD:

Answer 18

Monostotic FD
•Lesion progression usually stops at puberty
•Patients are usually asymptomatic for life
•Does not progress to polyostotic FD

Question 19

Clinical Course of Polystotic FD:

Answer 19

Polyostotic FD
•May progress into middle age
•Increased tendency for fractures & severe bone distortion

Question 20

Fibrous dysplasia: Radiological signs

Answer 20

The typical lesion will present as a medullary region that is:
•Lytic (severity varies depending on the ratio of fibrous : osseous tissue)
•Ground-glass/ frosted in appearance (i.e. uniformly opaque)
•Well circumscribed
•Diaphyseal or diametaphyseal location
•Minimally expansile

Question 21

Fibrous dysplasia, Complications:

Answer 21

• Pathological fracture

* Sarcoma (rarely)