All these elements make it possible to orient towards the benign or malignant nature of the lesion and to end up with a diagnostic range,
on which will depend the following explorations and the possible treatment.
Exposed bellow are Typical cases of the most common benign and malignant tumors selected with the objective of illustrating the main imaging features of the most relevant bone lesions in the pediatric population.
BENIGN TUMORS
Osteoid osteoma is a relatively common benign osteogenic tumor (8%) that has limited growth potential.
The most common clinical presentation is a triad made of nocturnal imflamatory bone pain that is acute and of sudden onset,
relieved by NSAIDs,
and disappearing after nidus removal.
Common sites are the femur and tibia.
Radiographs show a cortically based,
round or oval metaphyseal or diaphyseal radiolucent nidus surrounded by sclerotic bone.
Benign periosteal reaction or cortical thickening is frequently seen.
CT is the modality of choice to accurately identify the nidus for definitive diagnosis.
MRI is not preferred because surrounding bone marrow edema may obscure the nidus,
leading to a wrong diagnosis.
Enchondroma ( Fig. 6 ) is the second-most common benign bone tumor
(10%).
They frequently occur in the short tubular bones of the hands and feet.
On radiographs,
these cartilaginous tumors contain chondroid matrix with “ring-and-arc” or “popcorn” calcifications and are centrally located with endosteal scalloping.
They may assume more of a well-defined lytic (<5cm) and expansile appearance.
On MRI,
enchondromas tend to be lobular in contour and demonstrate high T2 signal.
They may have small foci of low signal,
which is related to the calcification in the chondroid matrix.
Although there is a possibility of malignant transformation in axial location,
this is very uncommon in the pediatric population.
Also referred to as exostosis,
are the most common benign bone tumors and account for 21-45% of such lesions.
Osteochondromas are most frequently found incidentally,
it develop during childhood but once formed remain for the rest of the individual's life.
Osteochondromas are of cartilaginous origin and are commonly located in the metaphysis of long bones especially around the knee.
They are described as either pedunculated or sessile lesions arising from the surface of the bone typically projecting away from the epiphysis,
and demonstrating continuity with the medullary cavity,
with a characteristical cartilage cap.
Ultrasound shows a hypoechoic region bounded by bone on its deep surface corresponding to the cartilage cap.
MRI is the best imaging modality to assess cartilage thickness ( suspicious for malignant degeneration if over 1.5 cm in thickness),
the presence of oedema in bone or adjacent soft tissues,
and visualising neurovascular structures in the vicinity.
- Nonossifying fibroma and cortical defect :(Fig. 8)
Also referred to as fibrous cortical defect if less than 2 cm in size.
Both encompassed by the term Fibroxanthoma,
are the second most common benign lesion in children( can be seen in up to 30% of the general population ) with a peak incidence at 10-15 years old.
The majority of NOFs are asymptomatic.
Larger lesions may be painful and potentially weaken the bone enough to predispose to pathological fracture.
NOFs are typically a multiloculated lucent lesion with a sclerotic rim. They are eccentrically located,
within the metaphysis of long bones,
adjacent to the physis,
particularly around the knee.
As the patient ages,
they seem to migrate away from the physis.
They have no associated periosteal reaction,
cortical breach or associated soft tissue mass
- Fibrous dysplasia (FD) : ( Fig. 9 )
It is rare (1/30.000 ),
benign,
slowly progressing bone disease ,
predominantly in children and young adults especially involving craniofacial skeleton,
long bones,
and costa .
It is common that FD could be a silent disease and is often an incidental finding,
but it also can cause significant bone pain,
deformity,
fracture and neurologic compressions
FD can present in monostotic form (70– 80% of FD) with one bone site or in polyostotic form with multiple bone sites.
Classically,
lesions have a ground-glass appearance on radiographs without periosteal reaction,
encircled by The classic "ring sign".
- Langerhans cell histiocytosis:(Fig. 10)
Also refered to as eosinophic granuloma,
represents less than 1% of biopsy-proven primary bone lesions.
They can be seen in the first few months of life through the 8th decade,
but the mean age is 5-10 years.
The lesions may be asymptomatic and discovered as an incidental radiographic finding as it can cause bone pain,
swelling and systemic symptome.
There is a propensity for location in the calvarium,
pelvis,
ribs,
and long bones such as the femur.
Within the skull the radiographs schows solitary or multiple punched out lytic lesions without sclerotic rim,
with button sequestrum representing residual bone and geographic skull.
Within long bones,
LCH is typically metaphyseal or diaphyseal and may be associated with periosteal reaction.
GCTs make up 14-22 % of all benign bone tumors and.
They almost invariably occur when the growth plate has closed and are therefore typically seen in early adulthood .
Radiographically,
GCTs are eccentrically located radiolucent lesions,
with abuts articular surface and well-defined with non-sclerotic margin(type 1B)
On MRI,
GCTs exhibit inhomogeneous increased T2 signal and inhomogeneous enhancement on postcont.
also referred to as Codman tumors, is a rare benign cartilaginous neoplasms. Despite being rare,
it is one of the most frequently encountered benign epiphyseal neoplasm in skeletally immature patients,
occurring in 70% of the cases in the humerus.
Clinical presentation is non-specific and may include joint pain,
muscle wasting and swelling.
Radiographs show a well defined lucent lesions,
with either lobulated margins and a thin sclerotic rim,
arising eccentrically in the epiphysis of long tubular bone.
Internal calcifications can be seen in 40-60% of cases.
CT demonstrates a better delineation of the relationship to the growth plate and articular surface,
solid periosteal reaction and internal calcification.
The cortical breach are also more easily appreciated.
MALIGNANT TUMORS :
It is the most common primary malignant bone tumor,
representing 20% of all primary malignant bone tumors.
Osteosarcomas can be divided into a number of subtypes according to the degree of differentiation,
location within the bone,
and histological variants.
The most common subtype is an intramedullary osteoid producing tumor,
which occurs at the metadiaphysis of long bones,
frequently around the knee.
Radiographically,
osteosarcomas are destructive,
eccentrically located lesions with poorly defined IIIb margins and an associated soft-tissue mass.
They frequently have osteoid or “cloud-like” bone formation and aggressive periosteal reaction,
classically a sun-burst or Codman triangle pattern.
Osteosarcomas may have skip lesions,
which are osseous or marrow metastasis within the same bone or adjacent bones in relation to the dominant lesion.
CT is predominantly utilised in assisting biopsy and staging.
MRI is helpful in determining extent of both the bone tumor and the associated soft-tissue mass.
It also can help identify skip lesions.
It is the second-most common highly malignant primary bone tumor in the pediatric population,
representing 8% of such tumors.Typically occurs in adolescents between 10 and 20 years of age with a slight male predilection.
Presentation is non-specific with local pain being by far the most common symptom.
They can have a variable radiographic appearance.
They typically occurs in the diaphysis of the long bones with moth-eaten or permeative bone destruction (76%) and an aggressive periosteal reaction,
classically known as the “onion-skin” pattern (57%).
It does not produce an osteoid matrix,
which is a key differentiation from osteosarcoma.
They occasionally demonstrate other appearances,
including Codman triangle,
spiculated,
or thick periosteal reaction.
MRI is important in evaluating Ewing sarcoma because it classically has a large soft tissue component,
more pronounced than the osseous destruction.
Post-gadolinium images demonstrate more pronounced tumoral enhancement,
which aids in distinguishing tumor from the surrounding marrow edema.
Bone metastases are relatively rare among children.
There is a wide range of primary malignancies that results in pediatric skeletal metastases.
The most common type is neuroblastoma,
rhabdomyosarcoma,
clear cell sarcoma of the kidney.
Primary bone tumors can also develop multiple bone metastases.
On radiographs,
these metastases,
located most commonly in the metaphyses of the extremities and in the spine,
display a destructive or diffusely permeative pattern without sclerotic margins and agressive periosteal reaction.