Introduction

There are many diseases and abnormalities of bone. Some are localized to the jaws while others can affect the whole skeleton. It is beyond the scope of this book to consider them all. This chapter summarizes a somewhat diverse, but important group of bone conditions which can affect the facial skeleton and which are of radiological importance.

Unfortunately, several of the bone diseases described, although totally different in nature, can present very similar appearances radiographically. To differentiate them, clinicians need to consider all relevant factors including: the age of the patient, the distribution of the disease (whether it is generalized or localized) and which bones are involved, as well as noting the specific radiographic features.

Using the atlas approach adopted in Chapter 24, an example of each of the conditions is shown together with a summary of the main radiographic features seen in the skull and facial skeleton. It is worth remembering that bone is a constantly changing, dynamic tissue. Thus diseases of bone can present a spectrum of radiographic appearances depending on the behaviour and maturity or stage of the disease and/or lesion(s). The examples shown represent only a small part of that spectrum.

The diseases of bone described include:

This is a rare developmental disturbance affecting the skull and clavicles. The abnormalities of dentition can be gross but usually affect only the permanent teeth. Examples are delayed eruption and multiple supernumeraries (see Fig. 28.1).

Osteopetrosis (Albers–Schönberg disease)

This hereditary disease is characterized by sclerosis of the skeleton (so called marble bones), fragile bones and secondary anaemia. Bone formation is normal but bone resorption is reduced, resulting in the presence of excessive calcified tissue and lack of marrow space (see Fig. 28.2). Cranial base changes may produce compression of the cranial nerves.

Main radiographic features

These can include:

• Evidence in the skull of:

– A uniformly dense and radiopaque skull vault

– Loss of the normal skull markings and structure

– Gross thickening and increased opacity of the cranial base with narrowing of the foramina

• Occasional involvement of the jaws. This involvement is always bilateral and includes:

– Thickening of the lamina dura around the teeth in the early stages (an almost pathognomonic finding in adults)

– Gradual thickening of the trabeculae and a reduction in the size of the marrow spaces producing an overall increase in bone density

– Usually normal teeth, but they may be deformed.

This spreading, progressive inflammation of bone and bone marrow, more frequently affects the mandible than the maxilla. It is caused usually by local factors such as periapical infection, pericoronitis, acute periodontal lesions, extractions or trauma. The inflammatory response may be acute or chronic depending on the virulence of the infecting organism and the resistance of the patient. It results ultimately in the destruction of the infected bone (see Figs 28.3 and 28.4). The reaction of the surrounding bone and periosteum is very variable and often age-related. There may be surrounding sclerosis of the bone forming poorly defined patchy opacity. Sequestra (small pieces of necrotic bone) can be exfoliated over a period of several weeks. The periosteum around the affected area can lay down new bone (the so-called periosteal reaction). In children this can be pronounced and is described as proliferative periostitis. This typically affects the mandible in young girls, following apical or pericoronal infection associated with the lower first molar producing a non-tender, bony hard swelling of the lower border. Radiographically the proliferative periostitis results in a laminated, so called onion-skin, appearance (see Fig. 28.5).

Osteoradionecrosis

The high doses of radiation used in radiotherapy reduce drastically the vascularity and reparative powers of bone. The mandible is particularly susceptible. Subsequent trauma (e.g. tooth extraction) or infection may produce osteomyelitis with rapid destruction of the irradiated bone, sequestra formation and poor healing. Radiographically, osteoradionecrosis resembles other types of osteomyelitis, although the border between necrotic and normal bone may be more sharply defined and subperiosteal new bone formation is not usually evident (see Fig. 28.6). A history of radiotherapy enables the differential diagnosis to be made.

Main radiographic features

These can include:

• Ragged, patchy or moth-eaten radiolucent areas of bone destruction

• Occasional evidence of radiopaque sequestra of dead bone

• Little evidence of healing.

Bisphosphonate-related osteonecrosis (Fig. 28.7)

Bisphosphonate-related osteonecrosis (BRONJ) is an avascular necrosis of the jaw in patients who are currently being, or have previously been, treated with a bisphosphonate drug. Clinically it is diagnosed when there is exposed or necrotic bone in the jaws that has persisted for more than eight weeks in a patient who has not received radiotherapy to the jaws.

Main radiographic features

These can include:

• Diffuse sclerosis of the bone

• Thickening of the lamina dura

• Poor or no healing at extraction sites

• Irregularity of the cortical bone

• Ill-defined radiolucency of the jaw with sequestra of bone

• Pathological fracture in late stages.

Primary hyperparathyroidism, caused by either hyperplasia or an adenoma of the parathyroids, or secondary hyperparathyroidism caused by kidney disease, results in increased secretion of parathormone. This causes generalized skeletal bone resorption leading to osteopenia (generalized decrease in bone density), bone pain or even pathological fracture and raises the plasma calcium levels (see Fig. 28.8). Localized cyst-like central giant cell lesions (brown tumours) can also develop in the jaws and long bones. The term osteitis fibrosa cystica is used to describe severe chronic skeletal hyperparathyroidism following brown tumour degeneration and fibrosis.

Acromegaly

This is a disturbance of bone growth caused by hypersecretion of growth hormone (GH) usually as the result of a pituitary adenoma developing after puberty. Characteristic features include renewed growth of certain bones, particularly the jaws, hands and feet, and overgrowth of some soft tissues (see Fig. 28.9).

Main radiographic features

These can include:

• Evidence in the skull of:

– Thickening of the bones of the skull vault which become enlarged and deformed

– Enlargement and distortion of the pituitary fossa

• Evidence in the jaws of:

– Enlargement of the mandible; the length of the horizontal and ascending rami are both increased causing it to become prognathic with an increased obliquity of the angle and with loss of the antegonial notch

– The body of the mandible may also be bent or bowed downwards anterior to the angle

– Enlargement of the inferior dental canal

– Thickening and enlargement of the alveolar bone with spacing and fanning out of the teeth, particularly anteriorly, resulting in an open bite.

This hereditary, chronic, haemolytic blood disorder affects principally black populations. It is characterized by abnormal haemoglobin which results in fragile erythrocytes that become sickle-shaped under conditions of hypoxia. These abnormal red blood cells have a decreased capacity to carry oxygen and are destroyed rapidly, producing anaemia.

In homozygotes, the radiographic changes reflect the haemopoietic system’s response to the anaemia including:

• Increased production of red blood cells and hyperplasia of the bone marrow at the expense of the cancellous bone

• Bone infarcts (see Fig. 28.10).

Thalassaemia (Cooley’s anaemia)

This hereditary haemoglobinopathy is characterized by chronic haemolytic anaemia and mainly affects people from the Mediterranean area. The defect lies in an inability to make enough normal globin chains, thus creating abnormal red blood cells which have a shortened life expectancy. Again the radiographic features result from the bone marrow proliferation required to produce more red blood cells with subsequent remodelling of all affected bones (see Fig. 28.11).

Main radiographic features

These can include:

• Evidence in the skull vault of:

– Widening of the diploic space

– Thinning of the inner and outer tables

– Remodelling of the trabeculae to give sparse lines which may radiate outwards from the inner table producing the hair-on-end appearance

• Evidence in the jaws of:

– Generalized coarse trabecular pattern with very large marrow spaces

– Expansion, which may lead to encroachment on, and subsequent obliteration of the maxillary antra

– Thinning of all cortical structures, most noticeably the lower border of the mandible

– Apparent spike-shaped or shortened tooth roots

– No evidence of bone infarcts.

As mentioned in Chapter 27, fibrous dysplasia is categorized as a bone-related lesion in the WHO 2005 Classification. It is described by the WHO as a genetically based sporadic disease of bone affecting single or multiple bones. It usually develops in childhood and is manifest before the age of ten. It is characterized by the proliferation of fibrous tissue and resorption of normal bone in one or more localized areas, and subsequent replacement with poorly formed, haphazardly arranged, new bony trabeculae. Clinical varieties include:

• Monostotic fibrous dysplasia, characterized by a lesion affecting a single bone, including the jaws, particularly the posterior part of the maxilla (see Figs 28.12 and 28.13).

• Polystotic fibrous dysplasia, characterized by multiple bone lesions and subdivided into:

– Jaffe type, without endocrine disturbances

– McCune–Albright syndrome, with endocrine disturbances and skin pigmentation.

Paget’s disease of bone (osteitis deformans)

In this disease of the elderly, the normal processes of bone deposition and resorption are disturbed severely, but only in certain bones and usually symmetrically. The main features are an enlarged head and thickening of the affected long bones, which bend under stress. Typically the early stages of the disease are characterized by bone resorption and the later stages by bone deposition, although there is no clear-cut distinction between the two stages (see Figs 28.14 and 28.15).

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Main radiographic features of early-stage Paget’s disease of bone

• In the skull vault, scalloped, circumscribed zones of osteoporosis spreading gradually across the calvarium, described as osteoporosis circumscripta

• Involvement of the maxilla and/or the mandible. If either is involved, the whole of the bone concerned shows radiographic changes which include:

– Generalized osteoporosis of the affected bones producing a fine trabecular pattern, described as ground glass

– Enlargement of the affected bone

– Loss of the lamina dura surrounding all the teeth.

Main radiographic features of late-stage Paget’s disease of bone

• Evidence in the skull vault of:

– Haphazard deposition of sclerotic bone in the earlier zones of osteoporosis producing an appearance resembling cottonwool patches

– Enlargement and distortion of the shape of the skull including basilar invagination

• Evidence in the jaws of:

– Haphazard deposition of sclerotic bone also resembling cottonwool patches

– Enlargement and distortion of the shape of the affected jaw, particularly the alveolus

– Encroachment of bone on the sinuses

– Separation and displacement of the teeth, often with extensive hypercementosis

– Loss of the lamina dura and periodontal ligament shadows.

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