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Paranasal sinus osteoma

Osteoma of the paranasal sinuses is a common benign tumour, usually found incidentally.

Epidemiology

Osteomas are commonly found in patients undergoing imaging of the sinuses, appearing in up to 3% of CT examinations of the paranasal sinuses 1. The are most frequently diagnosed in middle age (20-50 years of age) and there is a male predilection (M:F = 1.5-2.6:1) 1.

Clinical presentation

Most osteomas are asymptomatic and are found incidentally when imaging the sinuses either for sinonasal symptoms or for unrelated complaints.

Osteomas may become symptomatic in one of two ways:

  1. direct mass effect
  2. obstruction of normal sinus drainage

Three possible mechanisms for pain are suggested: local effect, referred pain via the trigeminal nerve and a prostagladin E-2 mediated mechanism5  There can be a significant inversely proportional  discrepancy between the size of the lesion and the symptoms; do not simply assume because the lesion is small it does not account for the patient's symptoms.

Some osteomas are large and exophytic. They may be palpable (as is the case with skull vault osteomas) or compress structures, such as content of the orbit 1-3. Rarely an osteoma may encroach upon the brain, and may even result in erosion of the dura with resultant CSF leak, pneumocephalus or intracranial infection (meningitis, cerebral abscess) 1-2,4.

More frequently they may impair normal drainage of one or more paranasal sinuses thereby resulting in acute or chronic sinusitis or even mucocoele formation 1,3.

Pathology

Distribution

Osteomas are frequently seen elsewhere in the head and neck, particularly the mandible and outer table of the skull vault. There is a particular frequency distribution within the paranasal sinuses 1-3:

  • frontal sinuses: 80%
  • ethmoid air cells: ~15%
  • maxillary sinuses: ~5%
  • sphenoid sinus: rare 2
Associations

There is a well recognised association with the Gardner syndrome 1. Approximately 30% of patients have a history of rhinosinusitis, although a causal link has not been established 1.

Sub types

Osteomas are, as the name suggests, osteogenic tumours composed of mature bone. Three histological patterns are recognised 1:

  1. ivory osteoma
    • also known as eburnated osteoma
    • most common 2
    • dense bone lacking haversian system
  2. mature osteoma
    • also known as osteoma spongiosum
    • resembles 'normal' bone, including trabecular bone often with marrow
  3. mixed osteoma
    • mixture of ivory and mature histology

Radiographic features

The radiographic appearance is that of a dense well circumscribed mass. Ivory osteomas are uniformly very dense, whereas mature osteomas may resemble 'normal' bone with marrow space sometimes visible.

CT

CT demonstrates a well circumscribed mass of variable density, varying from very dense (similar in density to normal cortical bone) to less dense with a ground-glass appearance. They are seen either with a sinus or less commonly exophytically growing out of a sinus.

MRI

On MRI, ivory osteomas are low on all sequence. Mature osteomas may demonstrate some marrow signal, but are also predominantly low on all sequence.

Treatment and prognosis

In asymptomatic cases excision is not necessarily indicated, and management varies from surgeon to surgeon. If sinonasal symptoms are present, then they can initially be managed medically (as if the osteoma is not present). In cases where the osteoma is thought to be responsible for symptoms (e.g. mucocoele) then resection is required. Some surgeons prefer to excise all osteomas.

Excision may be performed either endoscopically of externally.

Differential diagnosis

General imaging differential considerations include:

  • fibrous dysplasia: especially in less dense ground-glass osteomas
  • other osteogenic tumours

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