Part 6: Bone Tumours

BENIGN BONE TUMOURS

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

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)

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

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

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

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

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 distal tibia seen as eccentric expansile epiphyseal lucent lesion (arrows)

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

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 on xray (left) and low signal on MRI (right) due to osteoid formation

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)

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)

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