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Benign Bone Tumours
Chondroid Origin
(En)Chondroma
Definition
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Chondroma: a benign intramedullary neoplasm consisting of mature hyaline cartilage ▸ it is commonly centrally located (and then referred to as an enchondroma)
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It is the 2 nd commonest benign chondral lesion (after an osteochondroma)
Clinical Presentation
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An incidental finding ▸ a pathological fracture (60%) ▸ pain in the absence of a fracture or a rapid size increase is potentially malignant
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Age: 10–80 years (M = F)
Location
The tubular bones of the hands (40–65%): proximal phalanges > metacarpals or middle phalanges ▸ femur, tibia and humerus (25%) ▸ small bones of the feet (7%)
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A metaphyseal or diaphyseal location (rarely located within the epiphysis) ▸ often eccentric
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It is not found within the skull (it is only found within bones that are formed by endochondral ossification)
Radiological Features
XR
A well-defined oval or lobulated eccentric lytic lesion ▸ cortical expansion and chondral (popcorn) type calcification ▸ the overlying cortex may be thin and scalloped ▸ a narrow or sclerotic zone of transition ▸ no periosteal reaction (unless fractured) ▸ a solitary lesion in 75%
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‘Reverse Madelung’ deformity: a short distal ulna
MRI
Lobular margin ▸ T1WI: intermediate SI ▸ T2WI: high SI (due to the water content of hyaline cartilage) ▸ punctate areas of signal void (matrix mineralization) ▸ there is a hypointense rim with septations ▸ T1WI + Gad: septal enhancement
Scintigraphy
No increased uptake
Pearls
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Differentiation between a large enchondroma + grade 1 chondrosarcoma can be difficult ▸ lesion size >5–6 cm and deep endosteal scalloping are suggestive of chondrosarcoma
Periosteal chondroma
Rare and occurs in children and young adults ▸ it affects the long bone metaphyses (proximal humerus ▸ femur, tibia and the tubular bones of the hands and feet) ▸ no malignant potential ▸ the differential includes a periosteal chondrosarcoma/periosteal osteosarcoma
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XR: a 1–3 cm well-defined area of cortical erosion ▸ a mature periosteal reaction ▸ chondral-type calcification (50%) ▸ rarely a thin external shell of bone is present
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MRI: T2WI: a lobulated high SI mass adjacent to but not infiltrating the underlying cortex
Ollier's disease
Characterized by multiple enchondromas ▸ sporadic (and not inherited) ▸ usually unilateral ▸ bone growth may be impeded (with bowing or angulation)
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Malignant change (5–30%) ▸ an associated risk of a glioma, pancreatic or ovarian carcinoma
Maffucci's syndrome
A rare condition characterized by multiple enchondromas and soft tissue haemangiomas (phleboliths) ▸ unilateral in 50%
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Malignant change (20%) ▸ usually > 40 years
Chondromyxoid Fibroma (CMF)
Definition
A benign tumour composed of immature myxoid mesenchymal tissue with early cartilagenous differentiation
Clinical Presentation
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Pain and swelling (it can be asymptomatic)
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75% of patients present between 10 and 30 years of age (75%) ▸ (M : F, 2 : 1)
Location
60% are found within the long bones (25% are within the upper 
of the tibia) ▸ 40% are found within the flat bones (10% within the ilium) ▸ 17% are found within the small tubular bones of the hands and feet ▸ metaphyseal and eccentric in the medulla
Radiological Features
XR
An eccentric lobulated metaphyseal lytic lesion arising within the medulla ▸ it can cross into the epiphysis ▸ an associated well-circumscribed sclerotic border with thinning and expansion of the cortex ▸ the lesion long axis parallels the bone long axis ▸ periosteal reaction or soft tissue extension is uncommon ▸ matrix calcification in seen in 12% of cases
MRI
There are no characteristic features
Scintigraphy
Increased uptake
Pearl
Differential: chondrosarcoma ▸ adamantinoma ▸ fibrous dysplasia ▸ ABC
Osteochondroma
Definition
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A cartilage-capped exostosis (representing a bony outgrowth) ▸ usually a developmental anomaly ▸ it possesses its own growth plate and will stop growing with skeletal maturity
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The most common benign bone lesion
Clinical presentation
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It presents between 2 and 60 years (M : F, 2 : 1)
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It can present with mechanical problems: an enlarging mass ▸ pressure on any adjoining structures (e.g. nerves or blood vessels) ▸ bursa formation (due to irritation of local soft tissues)
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Rarely the stem can fracture
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Location
The long bones – especially around the knee (35%) ▸ the proximal humerus or femur ▸ the flat bones (e.g. the ilium or scapula)
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Lesions are initially metaphyseal but migration to the diaphysis occurs over time (classically pointing away from the joint)
Radiological features
XR
A continuous bony outgrowth from a normal cortex ▸ it can have a long slim neck (pedunculated) or be broad based (sessile) ▸ the marrow cavity extends into the exostosis (essential feature for diagnosis) ▸ the cartilage cap develops punctuate calcification with age
US/CT/MRI
These allow assessment of the cartilage cap – it should be < 5 mm (T2WI: high SI)
Scintigraphy
There will be variable activity
Pearls
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Differential: periosteal chondroma ▸ parosteal osteosarcoma
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Chondrosarcomatous change within the cartilage cap (occurring in <1% of cases) should be suspected if:
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There is an increase in pain or size (particularly after skeletal maturation)
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If the cartilage cap measures >1 cm (CT) or >2 cm (MRI)
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The development of ill-defined margins
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Diaphyseal aclasia (multiple hereditary exostosis)
A rare autosomal disorder with multiple osteochondromas occurring particularly at the ends of the long bones, ribs, scapulae and iliac bones (they may be larger than in the solitary form) ▸ this may lead to shortened or deformed limbs (e.g. a reverse Madelung deformity with a short distal ulna) ▸ the metaphyses can be widened and dysplastic
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Vertebral involvement is rare ▸ the cranial vault is spared ▸ malignant degeneration in 3–5%
Bizarre parosteal osteochondromatous proliferation (BPOP)
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A rare, tumour-like disorder
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Calcified masses arise adjacent to the cortex of the small bones of the hands and feet – there is no continuity between the lesion and the underlying bone ▸ there is no cartilaginous cap but it can resemble an osteochondroma
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Differential: soft tissue chondroma ▸ florid reactive periostitis
Dysplasia epiphysealis hemimelica (Trevor's disease)
Irregular overgrowth of part of an epiphysis which lies on one side of a single limb (resembling an osteochondroma) ▸ the leg is commonly affected
Chondroblastoma
Definition
A benign cartilage tumour with proliferation of immature cartilage cells (1% of all bone tumours)
Clinical presentation
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80–90% occur between 5 and 25 years (M : F, 3 : 1)
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It presents with joint pain (± a synovial reaction) ▸ commonly presents as a monoarthropathy (typically located in the epiphyses and provoking a synovial reaction)
Location
It is usually seen in skeletally immature patients, affecting the long bone epiphyses (40% are seen around the knee, and 33% within the proximal femur)
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Also found within apophyses and sesamoid bones (epiphyseal equivalents) such as the femoral greater trochanter and patella (the commonest patella tumour)
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It usually affects the calcaneus or talus in the foot
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The flat bones are mostly affected if >30 years old
Radiological features
XR
An eccentric spherical or lobular lytic lesion with a fine sclerotic margin centred within the epiphysis (40%) ▸ it extends into the metaphysis (55%) with partial closure of the growth plate
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Matrix mineralization (30%) ▸ linear periosteal reaction (30–50%)
MRI
T1WI: intermediate SI ▸ T2WI: variable SI including fluid levels due to secondary aneurysmal bone cyst change (15%) ▸ there is associated marrow and soft tissue oedema ▸ there may be a reactive joint effusion
Pearl
An ‘aggressive’ (atypical) chondroblastoma
A rare variant associated with cortical destruction and soft tissue involvement ▸ rarely associated with lung metastases
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Differential of a lytic epiphyseal lesion:
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Children: Brodie's abscess
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Adults: subchondral cyst ▸ clear cell chondrosarcoma
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Osteoid Origin
Osteoblastoma
Definition
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A benign bone tumour producing osteoid and woven bone ▸ it is histologically similar to an osteoid osteoma, but is differentiated by its size (> 1.5–2 cm) ▸ tends to show a more aggressive growth pattern ▸ does not resolve spontaneously
Clinical Presentation
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Any pain is usually more chronic and less severe than with an osteoid osteoma (and is rarely relieved by aspirin) ▸ there can be a painful scoliosis (with tumour at the concavity apex)
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80% of cases present at < 30 years of age (M : F, 2–3 : 1)
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Location
40–50% are within the spine and sacrum – 90% are eccentrically located within the neural arch with a painful scoliosis (± expansion or absence of the pedicle) ▸ potential extraosseous extension
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Other major sites: the diaphyses or metaphyses of the long bones (commonly the humerus)
Radiological Features
XR
A predominantly lytic lesion (>2 cm) ▸ larger lesions have greater matrix mineralization and may expand the bone with surrounding reactive sclerosis
CT
This often reveals occult calcification (punctate/nodular/generalized)
MRI
Reactive marrow and soft tissue changes (which may extend across several vertebrae) dominate ▸ there may also be secondary ABC changes ▸ T1WI: low or intermediate SI ▸ T2WI: intermediate or high SI ▸ T1WI + Gad: enhancement
Scintigraphy
This is always positive
Pearls
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An osteoblastoma may produce an extracortical mass causing spinal cord compression with a soft tissue component
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‘Aggressive osteoblastoma’: a locally aggressive lesion which is commonly within the sacrum and capable of producing metastases
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Differential (long bones): Brodie's abscess ▸ chondromyxoid fibroma ▸ Langerhans' cell histiocytosis
Bone Island (Enostosis)
Definition
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A congenital developmental focus of medullary cortical bone
Clinical Presentation
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An asymptomatic incidental finding
Location
It is commonly seen within the pelvis, femur and other long bones
Radiological Features
XR
A dense sclerotic focus with a spiculated margin blending with the trabeculae of adjacent bone
MRI
It is hypointense on all sequences (equivalent to cortical bone)
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Unlike a sclerotic metastasis, it will tend to have straight edges and the very dense bone can cause adjacent susceptibility artefacts
Scintigraphy
There is usually no uptake (25% of giant bone islands show increased uptake)
Osteopoikilosis and osteopathia striata
An autosomal dominant condition with multiple bone islands located in a periarticular distribution ▸ they can appear either round (osteopoikilosis) or elongated (osteopathia striata) in shape
Osteoid Origin/Tumours of Neural Tissue
Osteoma
Definition
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A slow-growing tumour consisting of predominantly cortical or, less often, cancellous bone ▸ it represents a dysplastic developmental anomaly
Clinical Presentation
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It is usually asymptomatic, although it can affect sinus drainage (leading to mucocoele formation) ▸ it can also cause CSF rhinorrhoea, pneumocephalus or meningitis
Location
Cortical (ivory) osteomas commonly affect the paranasal sinuses (frontal and ethmoid > sphenoid sinuses) ▸ it is less often found within the mandible, long bones or spine (causing backache)
Radiological Features
XR/CT
A homogeneous smooth dense lesion with a well-defined spherical margin ▸ it is attached to underlying bone ▸ it rarely exceeds 2–3 cm diameter
Pearl
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Multiple osteomas occur in Gardner's syndrome
Osteoid Osteoma
Definition
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A benign hamartoma affecting the cortex (80%), medullary cavity or subperiosteum ▸ it produces osteoid and woven bone
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