Week 1 - E - Benign bone tumours - Osteo/enchondroma, simple/aneurysmal cyst, giant cell, fibrous dysplasia, osteoid osteoma

Question 1

Are malginant primary bone tumours rare or common? Are metastatic bone tumours rare or common?

Answer 1

Malignant primary bone tumours are considered very rare when alongside other forms of primary malignancy

Metastatic bone tumours on the other hand are common

Question 2

What is the commonest benign bone tumour?

Answer 2

The commonest benign bone tumour is an osteochondroma - this is an overgrowth of cartilage and bone

Question 3

Where in the bone do osteochondromas typically occur? What forms over the osteochondroma?

Answer 3

Osteochondromas typically occur on the external surface of the bone near the growth plate and they have a cartilaginous cap

Question 4

How do osteochondromas present? What is the risk of malignant trasnformation?

Answer 4

Osteochondromas typically present as a painful mass

The risk of malignant transformation is small at 1%

Question 5

What do osteochondromas look like on xray?

Answer 5

On Xray the osteochondromas appear as a bony spur arising from the cortex and usually pointing away from the joint

Question 6

How are osteochondromas managed?

Answer 6

In most cases of osteochondroma, no treatment is required other than regular monitoring of the tumor to identify any changes or complications.

Surgical excision is usually only required if the lesion is growing or producing symptom eg pain or pressing on adjacent structure

Question 7

What is an enchondroma? What does it originate from?

Answer 7

An enchondroma is an intramedullary and usually metaphyseal bone tumour that originates from cartilage

Question 8

What causes the enchrondroma to form from the cartilage?

Answer 8

The enchondroma forms due to failure of normal endochondral ossification of the cartilaginous growth plate

Question 9

How are enchrondromas usually picked up?

Answer 9

Most enchondromas are incidental findings and the lesions are asymptomatic however they can weaken the bone resulting in a pathological fracture

Question 10

How do enchrondomas appear on xray?

Answer 10

The lesion is usually lucent however can undergo mineralisation with a patchy sclerotic appearance - appear as an intramedullary lesion

Question 11

What is the treatment of an enchondroma?

Answer 11

Treatment of enchondroma may involve surgery - once a fracture has healed or if there is risk of impending fracture, the enchondroma may be scraped out (curettage) and filled with bone graft to strengthen the bone

Question 12

What are simple bone cysts also known as? What is a simple bone cyst?

Answer 12

Simple bone cysts are also known as unicameral bone cysts

They are a single cavity benign fluid filled cyst in bone

Question 13

Where do simple bone cysts typically occur? How do simple bone cysts look on xray?

Answer 13

It usually occurs in the long bones near a joint and growth plate - at the metaphyses such as proximal humerus or proximal femur

On xray they appear less dense than bone as fluid filled in the metaphyseal region

Question 14

What age group do simple bone cysts tend to affect and how do they present?

Answer 14

They typically occur in children or young adults Simple bone cysts may be asymptomatic and an incidental finding on xray however they can cause weakness leading to pathological fracture

Question 15

How are simple bone cysts treated?

Answer 15

Simple bone cysts are treated again with curettage and bone grafting to strengthen the bone

Question 16

What is an aneursymal bone cyst? Why is its name a misnomer?

Answer 16

An aneurysmal bone cyst is a benign, blood-filled lesion in the bone that tends to expand or grow.

While it is referred to as a cyst, it is a misnomer as it is a true benign bone tumor surrounded by a thin wall of bone

Question 17

What is thought to cause the aneursymal bone cyst?

Answer 17

Aneurysmal bone cyst is thought to be due to a small arteriovenous malformation

Question 18

Which bones are typically affected by aneursymal bone cyst? Why is this type of bone tumour potentially worrying?

Answer 18

Aneurysmal bone cysts occur in the metaphyses of many different long bones, as well as flat bones (ribs and skull) and vertebral bodies

They are worrying as they are locally aggressive causing cortical expansion and destruction and are usually painful

Question 19

What is the treatment of aneurysmal bone cysts?

Answer 19

Treatment like enchondromas, and unicameral bone cysts is with curettage and filling with bone graft to strengthen the bone

Question 20

What is a giant cell tumour of the bone?

Answer 20

Giant cell tumour of the bone is a relatively uncommon tumor of the bone characterised by multinucleated giant (Osteoclast like) cells (hence also called osteoclastoma)

Question 21

Which region of the bones do giant cell tumours typically affect? and which bones?

Answer 21

Giant cell tumours typucally have a predilection for the metaphyseal region but tend to involve the epiphysis and can extend to the subchondral bone adjacent to the joint

GCTs most commonly occur around the knee and in the distal radius - can occur in other long bones

Question 22

How does giant cell tumours of the bone present and what is found histologically?

Answer 22

Giant cell tumours present painfully and may cause pathologically fracture

The aetiology is unknown but as the name suggests histologically they consist of muli‐nucleate giant cells.

Question 23

What is the appearance seen on ray of giant cell tumours?

Answer 23

Giant cell tumours have the characteristic soap bubble appearance on xray

Question 24

Describe the difference in where simple bone cysts, aneursymal bone cysts and giant cell tumours expand

Answer 24

Simple bone cysts occur at the metaphyses of long bones and fills the medullary cavity

Aneursymal bone cysts occur in the metaphyses as well and expand the cortical bone

Giant cell tumours involve the metaphyseal region but tend to involve the epiphyses & subchodnral bone at the joints

Question 25

What percentage of giant cell tumours metastasise and do they become benign or malignant?

Answer 25

Although they are considered benign, 5% can metastasize to the lung with benign pulmonary GCT

Question 26

What is the treatment of giant cell tumours?

Answer 26

Treatment is intralesional excision with use of phenol, bone cmeent or liquid nitrogen to destroy remaining tumour material and reduce the risk of recurrence

Question 27

What happens in fibrous dysplasia of the bone?

Answer 27

Fibrous dyspasia of a bone is a disorder where a genetic mutation results in normal bone and marrow being replaced by lesions of fibrous tissue resulting in formation of bone that is weak and prone to expansion

Question 28

What is it known as when fibrous dysplasia of bone affects * One bone * More than one bone What age group does it tend to present at?

Answer 28

Affecting one bone - monostotic

Affecting more than one bone - polystotic

Question 29

What does the defective mineralisation of the bone in fibrous dysplasia result in?

Answer 29

Defective minerlisation results in angular deformities and the affected bone is wider with thinner cortices

Question 30

What is the presentation of fibrous dysplasia of the bone?

Answer 30

Typically presents with pain and increased risk of fracture

Question 31

What can extensive involvement of the proximal femur in fibrous dysplasia produce?

Answer 31

Shepherd’s crook deformity of the bone

Question 32

What is the treatment of fibrous dysplasia of the bone?

Answer 32

Biphosphonates may reduce pain

Pathological fractures should be stabilised with internal fixation and cortical bone grafts used to improve strength

Question 33

What is an osteoid osteoma?

Answer 33

An osteoid osteoma is a benign bone tumor that arises from osteoblasts

Question 34

Which age group is affected typically by osteoid osteomas and which bones?

Answer 34

Typically occurs in adolescence and affects the long bones esp the proximal femur

Question 35

What are the presenting features of an osteoid osteoma?

Answer 35

Predominant clinical feature is intense constant pain, worse at night due to the inflammatory response

Question 36

What do osteoid osteomas look like on radiographs? What confirms diagnosis?

Answer 36

On radiographs, ostoeid osteomas appaer as a small nidus of immature bone (osteoblasts) surrounded by a intense sclerotic halo

Diagnosis is confimed by bone scan (intense local uptake) and CT scan

Question 37

How are osteoid osteomas treated?

Answer 37

Pain is greatly reliaved by NSAIDs

CT radiofreqnecy abalation is the treatment of choice

Question 38

Brodie’s abscess and Brown tumours can present with a lytic lesion of bone. What are these conditions?

Answer 38

Brodie’s abscess is a rare form of osteomyelitis. (subacute osteomyeleitis) It involves a subacute infection of the bone with development of a localized abscess, usually within the metaphysis of long bones

Brown tumours form in hyperparathyroidism due to excessive osteoclast activity