Osteosarcomas are malignant bone-forming tumors that typically occur in the metaphysis of long bones in young patients. They can be primary tumors or develop secondary to conditions like Paget's disease. Patients usually present with bone pain and swelling. Treatment requires aggressive surgical resection and chemotherapy, with the goal of cure. Imaging plays an important role in evaluating tumor extent, involvement of surrounding tissues, and distant staging.

3.  Osteosarcomas are malignant bone forming
tumours and the second most common
primary bone tumour after multiple
myeloma . They account for ~20% of all
primary bone tumours.

4.  Osteosarcomas can be either primary or secondary,
and these have differing demographics.
 Primary osteosarcoma - typically occurs in young
patients (10-20 years) with 75% occurring before
the age of 20; which is logical because the growth
centers of the bone are more active during the
puberty to adolescence time period. Therefore the
epidemiology can be easily understood. For less
clear reasons, there is a slight male predominance.
 Secondary osteosarcoma - occurs in the elderly,
usually secondary to malignant degeneration
of Paget's disease, extensive bone infarcts or post
radiotherapy for other conditions.

5.  Patients usually present with bone pain, occasionally
accompanied by a soft-tissue mass or swelling. At
times, the first symptoms are related to pathologic
fracture.
 The distribution of primary and secondary
osteosarcomas is also different.
 Primary tumours typically occur in the metaphyseal
regions of long bones, and have a striking
predilection for the knee, with up to 60% occurring
there
 Secondary tumours on the other hand, have a much
wider distribution largely mirroring the combined
incidence of their underlying condition, and thus
much have a higher incidence in flat bones, especially
the pelvis (a favourite site of Paget's disease).

6.  Osteosarcomas can be divided into a number of sub
types according to degree of differentiation, location
within the bone, and histological variants 3.
 These sub types vary in imaging findings,
demographics and biological behaviour, and include :
 Intramedullary ~ 80%
◦ conventional high-grade - most common and discussed in
this article
◦ telangiectatic osteosarcoma
◦ low-grade osteosarcoma
 Surface or juxtacortical ~ 10-15%
◦ intracortical osteosarcoma
◦ parosteal osteosarcoma
◦ periosteal osteosarcoma
 Extra skeletal ~ 5%
◦ extra skeletal osteosarcoma

7.  Macroscopically
osteosarcomas are bulky
tumours where a
heterogeneous cut
surface demonstrates
areas of haemorrhage,
fibrosis and cystic
degeneration. Their
extension within the
medullary cavity is often
much more extensive
than the bulky part of the
tumour would suggest.
Areas of bone formation
are characteristic of
osteosarcomas, with the
degree of bone formation
varying widely.

8.  Microscopically
poorly formed
trabecular bone is
seen with (in the
typical high grade
conventional sub
type) cellular
pleomorphism and
mitoses. Variable
amounts fibrocytic
and chondroblastic
appearing cells may
also be encountered.

9.  They typically occur at the metadiaphysis of
tubular bones in the appendicular skeleton.
Common sites include
 femur: ~ 40% (especially distal femur)
 tibia: ~ 16% (especially proximal tibia)
 humerus: ~ 15%
 Other less common sites include
 fibula
 innominate bone
 mandible (gnathic osteosarcoma)
 maxilla
 vertebrae

10.  Plain Film:
 Conventional radiography continues to play an
important role in diagnosis. Typical appearances of
conventional high grade osteosarcoma include:
 medullary and cortical bone destruction
 wide zone of transition, permeative or moth-eaten
appearance
 aggressive periosteal reaction
◦ sunburst type
◦ Codman triangle
◦ lamellated (onionskin) reaction - less frequently seen
 soft-tissue mass
 tumour matrix ossification / calcification
◦ variable: reflects a combination of the amount of tumour
bone production, calcified matrix, and osteoid

11.  The role of CT is predominantly in assisting
biopsy and staging, but adds little to plain
radiography and MRI in direct assessment of
the tumour. The exception to this rule is
predominantly lytic lesions in which small
amounts of mineralized material may be
inapparent on both plain film and MRI

12.  MRI is proving essential in accurate local staging and
assessment for limb sparing resection, particularly for
evaluation of intraosseous tumour extension and soft-tissue
involvement. Assessment of the growth plate is also essential
as up to 75 - 88% of metaphyseal tumours do cross the
growth plate into the epiphysis .
 T1
◦ soft tissue non-mineralized component : intermediate signal
intensity
◦ mineralised / ossified components : low signal intensity
◦ peri-tumoural oedema : intermediate signal intensity
◦ scattered regions of haemorrhage will have variable signal
(see ageing blood on MRI)
◦ enhancement : solid components enhance
 T2
◦ soft tissue non-mineralized component : high signal intensity
◦ mineralised / ossified components : low signal intensity
◦ peri-tumoural oedema : high signal intensity.

13.  Work-up: local staging by MRI prior to biopsy
and distant staging with bone scan and chest CT.
 Cure, if achievable requires aggressive surgical
resection often with amputation followed by
chemotherapy. If a limb-salvage procedure is
feasible, a course of multi-drug chemotherapy
precedes surgery to downstage the tumour,
followed by wide resection of the bone and
insertion of an endoprosthesis. Currently, the 5-
year survival rate after adequate therapy is
approximately 60-80% 4.
 The most frequent complications of conventional
osteosarcoma are pathologic fracture and the
development of metastatic disease, particularly
to bone, lung and regional lymph nodes.

14.  General differential considerations
include
 osteomyelitis
 Other tumours
◦ metastatic lesion to bone
◦ Ewing sarcoma
◦ aneurysmal bone cyst

15.  Haemophilic pseudotumour is a rare
complication that occurs in 1-2%
ofhaemophiliacs.
 Pathology
 Most develop in the muscles of the pelvis and
lower extremity, where the large
muscles have a rich blood supply, or in bone
following intraosseous bleeding.

16.  Plain film
 X ray is useful in diagnosing intraosseous
pseudotumours. Pseudotumours appear as well
defined,unilobular or multiloculated, lytic,
expensile lesions of variable size. It can involve
metadiaphysis and epiphysis of long bones.
 Other findings include endosteal scalloping,
perilesional sclerosis, cortical thinning or
thickening, trabeculations and septations.
Pathological fractures can also be present.
 Ultrasonography, CT, and MR imaging have
important roles in detecting pseudotumours,
especially when they are in the pelvis.

17.  CT is useful in detecting both the extent of
soft-tissue masses and the involvement of
bone. Pseudotumours contain
coagulated blood and are surrounded by a
thick wall. Contrast-enhanced CT is useful in
determining the thickness of the wall. In the
acute stage, the center of the pseudotumour
is hypodense on CT, but the
periphery is isodense and indistinguishable
from surrounding muscle.

18.  In the acute and subacute stages, sonography
shows a central anechoic area with increased
echoes behind the lesion, caused by fluid in
the pseudotumour. A distinct plane separates
the mass from the surrounding muscles.
 CT shows the thick wall more consistently
than does ultrasonography. Multiple irregular
echoes represent solid material that cannot
be documented on CT. Differential diagnosis
from abscess may be difficult.

19.  The hypointense rim of a pseudotumor on
both T1 and T2-weighted images consists of
fibrous tissue that contains haemosiderin .