Benign Lytic Lesions and Bone Tumours

Bone Tumours and Benign Lytic Lesions

Factors aiding diagnosis| Benign lesions | Malignant tumours | Osteomyelitis

Non-ossifying fibroma | Solitary bone cyst | Aneurysmal bone cyst
Enchondroma | Haemangioma | Fibrous dysplasia | Giant cell tumour

Osteosarcoma | Ewing's sarcoma | Chondrosarcoma | Metastases | Multiple myeloma

(click on images to enlarge)

When interpreting whether an image is normal or abnormal, it is common to come across incidental lytic lesions, which, depending on their appearance, must be classified as either a normal variant, or something which warrants further investigation.

It is difficult to determine radiologically with plain film imaging if a lytic lesion is benign or malignant. It is more accurate to describe whether the process looks aggressive or non-aggressive. Some factors, as outlined below, help to determine whether a lesion looks aggressive or non-aggressive, and therefore the differential diagnosis.

It is important to remember, however, that some benign processes such as osteomyelitis, can mimic malignant tumours, and some malignant lesions, such as metastases or myeloma, can look benign.

Factors aiding in the diagnosis of bone tumours and benign lytic lesions:

Age of patient

Specific lesions tend to occur in specific age ranges. Solitary bone cysts, non-ossifying fibromas, aneurysmal bone cysts and Ewings tumours occur in patients under the age of 30 years. Metastases and myeloma will usually occur in patients over the age of 40

Location within the bone

Epiphyseal, metaphyseal or diaphyseal
Central within the bone, eccentric or cortical
Lesions often arise within specific bones, and within specific areas of that bone. Giant cell tumours for example, usually arise within the distal femur or proximal tibia, and will always abut (push against) the articular surface

Size of lesion

Size of lesion is not necessarily an indication of how aggressive the process is, but recognition that specific lesions have a tendency to grow larger can help lead to the correct diagnosis. Solitary bone cysts within the proximal humerus, for example, often become large. A large lytic lesion is at risk of fracturing and it is therefore often prophylactically packed to prevent fracture and subsequent deformity

Monostotic (one lesion) or polyostotic (multiple lesions)

Multiple lesions are also not necessarily indicative of an aggressive process. Although metastases and myeloma are usually multiple, most aggressive processes demonstrate a single lesion. Similarly, benign enchondromas often become multiple within the phalanges

Zone of transition from normal to abnormal bone

This is often the best indicator as to whether a lesion is aggressive or non-aggressive. A very definite, sharp, and therefore narrow area (zone) between the normal and abnormal bone indicates a non-aggressive lesion. A wide, hazy, and undefined zone of transition suggests a more aggressive process. However, be aware that some benign processes (osteomyelitis) have a wide zone of transition as they are fast acting

Reactive sclerosis

If there is a sclerotic margin to the lesion, it is most likely non-aggressive

Pattern of bone destruction

Geographic = Well defined margin; non-aggressive lesion
Moth-eaten = Less defined margin
Permeative = Poorly demarcated with multiple small irregular holes. Suggests aggressive process

Presence of visible tumour matrix

Cartilage = Stippled (CJ) matrix
Osteoid = Sclerotic

Host (bone) response

Cortical thinning, expansion and penetration. Cortical destruction suggests an aggressive process. Be aware, however, that what may appear to be cortical destruction may actually be cortical bone replacement by a fibrous or chondroid matrix, which is non-calcified and may be located within a benign lesion. This gives the false impression of cortical destruction when it is actually cortical replacement. Aneurysmal bone cysts, for example, often cause such thinning of the cortex as to make it undetectable radiographically.

Periosteal reaction

Periosteal reaction will occur whenever the periosteum is irritated. This may be due to a malignant process, a benign lytic lesion, osteomyelitis, or trauma. The appearance of the periostitis will give an indication as to cause:
Benign periostitis looks thick, wavy, dense and uniform, as it is slow growing and therefore gives the periosteum time to lay down new bone.
Aggressive periostitis is often described as lamellated (onion-skinned), amorphous and sunburst as the periosteum does not have time to consolidate.

Soft tissue involvement

Aggressive lesions often lead to cortical breakthrough to create soft tissue mass

BENIGN LYTIC LESIONS

Non-Ossifying Fibroma / Fibrous Cortical Defect

One of the most common benign lytic lesions seen
Asymptomatic and usually an incidental finding
Most often seen around the knee and distal tibia
Non-Ossifying fibroma generally bigger than 2cm
Fibrous Cortical Defect generally smaller than 2cm
Arises in under 30 year age group
Develops from cortex of metaphysis; is eccentric within the bone
Bubbly
Usually has thin, sclerotic border that is often scalloped and slightly expansile
Become sclerotic as healing occurs and “disappears” as it ossifies
Therefore not seen in over 30 age group

Simple / Solitary Bone Cyst

Arises in under 30 year age group
Begins within the physeal growth plate and extends into diaphysis
Centrally located within a long bone
Most commonly occurs in the proximal humerus
In the calcaneum it is triangular, and located antero-inferiorly as this is an area that does not receive stress, and therefore develops atrophy of the bony trabeculae
Also called unicameral bone cyst, however there is not always just one compartment
Asymptomatic, unless it is fractured, which often occurs
"Falling fragment sign": cortical fragments produced from pathological fracture, that have sunk to the bottom of the fluid filled lesion

$solitary bone cyst - proximal humerus with pathological fracture$

Aneurysmal Bone Cyst

Arises in under 30 year age group
Presents with pain
Expansile
Differential diagnosis: osteoblastoma, as very similar in appearance

Enchondroma

Most commonly seen in the phalanges
Asymptomatic but commonly fractures
Well-defined with narrow zone of transition
Lobulated
Can become slightly expansile
Causes endosteal scalloping and cortical thinning
Ollier’s Disease = Multiple enchondromas
Maffucci’s Syndrome = Multiple enchondromas with soft tissue haemangiomas
Contain calcified chondroid matrix (irregular, speckled) when located away from phalanges

$enchondroma - proximal phalanx with pathological fracture$ $Ollier's disease with pathological fracture$
Differential diagnosis: bone infarct. This often occurs within femur or tibia and typically demonstrates patchy sclerosis with demineralisation

Haemangioma

Benign vascular tumour
Vertebral haemangioma; solitary lesion within vertebral body typically demonstrates coarse vertical trabecular pattern
Usually asymptomatic and incidental finding
However, within vertebral body occasionally causes symptoms of spinal cord compression

Fibrous Dysplasia

Long lesion in a long bone (often occurs in proximal femur)
Expansion and bone deformity
Lytic but becomes ground-glass in appearance as the matrix calcifies, and then becomes sclerotic
Asymptomatic, but can fracture
No periosteal reaction
May be single or multiple lesion in different locations

$fibrous dysplasia - tibia, with pathological fracture$

Giant Cell Tumour

Epiphyses must be closed
Must be epiphyseal and abut the articular surface
Well-defined with narrow zone of transition
Must have a non-sclerotic margin
Eccentric within the bone
Usually occurs within the distal femur or proximal tibia
15per cent become malignant based on recurrence rate or subsequent metastases

MALIGNANT BONE TUMOURS

Osteosarcoma

Most common malignant primary bone tumour
Arises in under 30 year age group, but also has a second peak at 60 years
Presents with pain
Usually occurs towards end of long bone
Aggressive with a wide zone of transition
Often demonstrates cortical destruction
Sclerosis present from either tumour new bone or reactive sclerosis

Ewing's sarcoma

Arises in under 30 year age group
Permeative lesion usually in diaphysis of long bone
Often have “onion-skinned” or “sunburst” type of periostitis

Chondrosarcoma

Looks similar to enchondroma, but is painful
Seen in over 40 year age group
Lytic, destructive lesion with calcified chondroid matrix that looks amorphous and irregular with “snowflake”-like calcification

Metastatic Disease

May demonstrate single or multiple, lytic or sclerotic lesions
Can look benign or aggressive
When aggressive, often is described as having moth-eaten or permeative appearance
Difficult to ascertain origin of primary
Metastases from a primary renal tumour will always demonstrate lytic lesions
Breast primary often develops lytic metastases
Multiple sclerotic lesions, particularly in the pelvis (in an elderly man) will usually have prostate primary
Painful, and often develops pathological fracture with little trauma

Multiple Myeloma

May be solitary or multiple lytic lesions (plasmacytomas)
Radiologically, often precedes clinical or haematological presentation of myeloma
Not always “hot” on radionuclide imaging; skeletal survey more useful for diagnosis
Diffuse and permeative lytic lesions
Usually age range over 35 years