Distinguishing
between benign and malignant tumours
This can be very difficult in the growing child, and is best handled
with a team approach among the surgeon, radiologist and pathologist.
History
Malignant tumours are usually painful. Benign tumours are not. The pain
of malignant tumours is very characteristic. Its most noticeable at rest,
particularly at night. The site and the age of the patient will also give clues
to the likely pathology.
Examination
A lump which has been present for a long time is unlikely to be
malignant. Unfortunately, some benign tumours can turn malignant, so a sudden
change in size or increase in tenderness in what was previously thought to be
a benign tumour should raise suspicions.
Investigations
X-rays
Benign tumours have well-circumscribed margins and may even have a thin
rim of sclerosis around a lyric lesion. Malignant lesions do not have clear
margins. A subtle, but important, sign is periosteal lifting over the site of
the lesion (Fig. 25.2). This indicates inflammation and can be a clear sign of
malignancy.
Periosteal
lifting can also occur over a stress fracture and if there is underlying
infection, so both these possibilities must be borne in mind when making a
differential diagnosis.
Osteochondroma
These benign tumours are common and frequently multiple. The commonest
site is in the femur or the tibia around the knee. There are commonly on a bony
pedicle which grows away from the epiphyseal plate and which is covered in a
large cartilage cap (Fig. 25.3). If they are large they can interfere with the
function of the knee. Occasionally they become malignant and if they become
painful the possibility of malignant change should be considered.
Osteoid
osteoma
These benign tumours occur in children, adolescents and young adults.
They are commonest in the femur and tibia but can occur elsewhere, even in the
spine. They are unusual as benign tumours in that they produce a constant aching
pain,
Chondromas
As their name suggests, these tumours are made up mainly of cartilage
and are common in the hands and the feet. The medulla of the bone may be
scalloped out (enchondroma) and there may be cortical thinning which may produce
a
Fibroma
These appear as well-circumscribed lyric lesions in the cortex of bone.
They can be difficult to distinguish from fibrous dysplasia, which usually has
new bone within the lyric lesion. Another dysplasia, which can cause confusion
with a tumour, is the aneurysmal bone cyst. This is an expanding lyric lesion
most commonly found in the ends of growing long bones.
Osteoclastoma
or giant cell tumour
These benign tumours are filled with undifferentiated spindle cells and
multinucleate giant cells (Fig. 25.5). They are commonly found in the
epiphysis of a bone, lying close to the epiphyseal plate. The cortex over the
tumour may be destroyed and there may be periosteal elevation. They can be
treated by block excision but, unfortunately, they are commonly closely
associated with a joint. If they are rapidly growing or recur after excision
they may be malignant and require more aggressive treatment.