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Osteoradionecrosis

Osteoradionecrosis (ORN) refers to a severe delayed radiation-induced injury and is characterised by bone tissue necrosis and failure in healing. There is some overlap with the term radiation osteitis.

Pathology

One of the key factors is thought to alteration in blood supply to the bone from microvascular damage. limit the ability of tissues to adjust to normal wear and turnover, resulting in tissue breakdown

Usually large radiation doses are required for osteoradionecrosis to occur (e.g. < 3000-5000 cGy) 2.

Location

While it can involve any bone which is in an irradiation field, there are specific sites in which osteoradionecrosis is more commonly seen. These include:

  • mandible: mandibular osteoradionecrosis : this site is particularly prone due to its superifical location and high doses of radiation required to radically treat naso-oro-pharyngeal tumours. 
  • chest wall-shoulder-humerus-scapula
  • spine
  • bony pelvis

Radiographic features

While there are general features, radiographic features can somewhat vary with the site of involvement.

Plain film

With mandibular osteoradionecrosis, there can be ill-defined cortical destruction without sequestration. In osteoradionecrosis of the ribs, clavicle, scapula, and humerus, radiography may demonstrate 2 :

  • osteopaenia : typically occurs after ~1 year after irradiation 4
  • disorganization and coarsening of trabecular architecture
  • cortical irregularity
  • heterogenous bone density.
CT

With mandibular osteoradionecrosis, CT may additionally show cortical interruptions and loss of spongiosa trabeculation 6. In other sites CT may show the presence of subtle fractures, alterations in bone architecture and dystrophic soft-tissue calcification.

MRI

On MRI, they can be development of new heterogeneous signal within the marrow of an irradiated area (intermediate or low T1 signal, intermediate or high T2 signal). Osteoradionecrosis with or without osteomyelitis can be extremely difficult to differentiate from recurrent tumour. Adjacent muscles may appear oedematous and show intense enhancement, which can be difficult to differentiate from recurrent tumor if bone changes are not visible on CT 10

In osteoradionecrosis of the spine, haematopoietic cellular elements of the spinal marrow can also be replaced with fat, which then has 2

  • T1: high signal intensity
  • T2:  intermediate signal intensity 

Prognosis

It either stabilizes or gradually worsens which then becomes notoriously difficult to manage.

Differential diagnosis

To give a meaningful differentiation, location and imaging modality needs to be taken into account. General differential consideration include:

  • original tumour recurrence
  • radiation-induced secondary tumour e.g. sarcoma
  • complicating infection: osteomyelitis (can also be an association) 10

See also

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