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, which is most noticeable at night and is sometimes relieved by aspirin. They can be very difficult to see on plain X-ray where they may look like an area of slight sclerosis (Fig. 25.4). However, on tomography it may be possible to see the characteristic radiolucent centre. Osteoid osteomas also show up very hot on radioisotope scans. Surgical excision relieves the pain but they can be difficult to find at surgery so careful preparation is needed.

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 pathological fracture. The condition of multiple enchondroma is called Oilier’s disease. Malignant change is not common but when many chondromata are present this risk is increased.

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.