Part 6: Bone Tumours

 

BENIGN BONE TUMOURS

  • Well defined, often sclerotic, margin
  • Expansile lesion may result in cortical thinning but no cortical destruction
  • A periosteal reaction may be present which appears uniform and solid

 

Enchondroma

Benign cartilaginous tumour

Typically found in the diaphyses of the metatarsals and phalanges

Well defined, radiolucent and mildly expansile with cortical thinning

May have internal calcification

Multiple enchondromas (as seen in Ollier’s disease) may have malignant potential

Multiple enchondromas (arrows) in Ollier’s disease

 

Osteochondroma

Cartilage-capped exostosis seen as a bony outgrowth

Cartilaginous component invisible on plain radiographs unless calcified

Rarely, the cartilage cap may undergo transformation to malignant chondrosarcoma; cartilage cap thickness > 2cm is suspicious and usually assessed on MRI

Pedunculated, subungual exostoses on the distal phalanx of the hallux are common and usually have a cartilaginous cap, classifying them as osteochondromata

Osteochondroma of first proximal phalanx (arrow)

 

Intraosseous lipoma

Typically occurs in the calcaneum

Well-defined lucent lesion; may contain central calcification

MRI diagnostic to confirm fatty matrix, seen as high T1 and T2 signal which supresses with fat saturation

Intraosseous lipoma calcaneum

 

Fibrous cortical defect

Common, up to 20 % of immature skeletons

Caused by fibrous tissue from the periosteum invading the underlying cortex; may be related to a subclinical injury

Usually an incidental finding

Seen as a cortically-based, radiolucent lesion with well-defined sclerotic border in the tibial metaphyses

Larger lesions (>2cm) that expand into the medullary cavity are referred to as non-ossifying fibromas

Fibrous cortical defect with well-defined sclerotic margin

 

Solitary (simple) bone cyst

Cyst of unknown origin containing clear or serosanguinous fluid

Occurs in the immature skeleton

May occur in distal tibia / fibula, calcaneum and long bones of the foot

Seen as a well-demarcated, radiolucent intramedullary lesion with cortical thinning

May present with a pathological fracture

Simple bone cyst distal fibula seen as well-defined, slightly expansile lucent lesion

 

Aneurysmal bone cyst

Usually in patients <30 years

Sponge-like cyst with blood-filled spaces and fibrous septae; may arise as the result of a vascular anomaly

Seen as radiolucent, often rapidly expansile lesion with a thin cortical shell

Matrix fluid-fluid levels on MRI are typical

Aneurysmal bone cyst with fluid-fluid levels on MRI

 

Osteoid osteoma

Typically in young patients who complain of severe rest and night pain

Dramatic relief with aspirin

Seen as ovoid radiolucent nidus up to 1cm in diameter surrounded by sclerosis and periosteal thickening

Sclerosis may mask the radiolucent nidus on plain radiographs; best seen on thin CT sections

Osteoid osteoma with radiolucent nidus (arrows) and surrounding sclerosis best seen on CT

 

Giant cell tumour of bone

Occur primarily in the mature skeleton

Typical eccentric epiphyseal location, extending to subarticular surface

Seen as radiolucent lesion with well-defined, but non-sclerotic, margin

May be expansile with cortical thinning

Approximately 15% of giant cell tumours are malignant

Giant cell tumour of distal tibia seen as eccentric expansile epiphyseal lucent lesion (arrows)

 

MALIGNANT BONE TUMOURS

  • Ill-defined margin
  • Permeative, ‘moth-eaten’ appearance
  • Cortical destruction
  • Periosteal reaction has lamellated (‘onion-skinned’) or spiculated (‘hair on end’ or ‘sunray’) appearance
  • Soft tissue mass: distortion of adjacent soft tissue contour with increased density; may have calcification

Osteosarcoma

Uncommon in the foot

Typically occurs in immature skeleton; may occur in older age group usually secondary to Paget’s

Seen as ill-defined, often mixed lytic and sclerotic lesion

As tumour osteoid becomes mineralized, there is increasing sclerosis and new bone formation with a ‘cloud-like’ density

Aggressive periosteal reaction with wedge of ossified tissue under the periosteum called a Codman’s triangle.

Osteosarcoma calcaneus with sclerosis due to osteoid formation

 

Ewing’s sarcoma

Occur in immature skeleton

Seen as an ill-defined, permeative lesion in diaphysis of a long bone or within a flat bone

Often has cortical destruction and spiculated periosteal reaction

Osteomyelitis has a similar radiographic appearance

Ewing’s sarcoma with ill-defined, permeative infiltration of fibula (arrows) and cortical destruction (arrowheads)

 

Chondrosarcoma

Cartilaginous tumours are rare in the foot but have been noted in the calcaneum

Occur in the mature skeleton ~50-70y

Usually contain calcification which has a ‘popcorn’ or ‘snowflake’ appearance indicative of their cartilaginous origin

Chondrosarcoma posterior distal tibia with ‘popcorn-like’ chondroid calcification (arrows)

 

Metastases

Needs to be considered in the differential diagnosis of any lytic lesion in a patient >40 years

Metastases to the foot are most commonly from primary lung carcinoma

Usually lytic, destructive lesions

Sclerotic lesions most commonly prostate and breast metastases

Thyroid and renal metastases produce expansile lesions

Metastasis base 5th metatarsal seen as lytic destructive lesion (arrow) in patient with known lung carcinoma