CT scangenerated frontal sinus templates in osteoplastic flap surgery

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CT scan-generated frontal sinus templates in
osteoplastic flap surgery
British Rhinological Society May 2008

• Mat Daniel, Jason Watson , Anshul Sama
• Otorhinolaryngology and Maxillofacial Surgery
• Nottingham University Hospital

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Frontal sinus mapping inosteoplastic flap surgery

• Crucially important in FS osteoplastic flap
  surgery
• Caldwell radiograph from 6ft, positioned over FS
• Composite CT image of frontal sinus (Fewins 04)
• Controlled burr holes along proposed osteotomy
  line (or within FS area), connected with
  oscillating drill (Maniglia 91)
• Sinus probing
• Transillumination
• Image Guidance Systems (IGS)

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Frontal sinus mapping

• IGS more accurate than Caldwell, sinus probing,
  or transillumination (Ansari 03, Melroy 06)
• IGS reduces complications (Sindwani 04)
• IGS may not be available, and does not give
  actual 3D representation
• In contrast, most ENT units will have links with
  a maxillofacial laboratory

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Aim

• Develop a 3D template of the frontal sinus
• that can be used intra-operatively as an
• onlay guide to FS mapping

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Model Template production

• Import CT images,
• identify required region

Print 3D sinus model layer by layer
Onlay malleable light-cure resin sheet and process
Drill FS on light-cure sheet to form custom
template
Sterilise for direct use in theatre
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Clinical use

• Close collaboration with prosthetics /
  maxillofacial laboratory
• Original model available in theatre
• Onlay template sterilised
• Template placed onto FS after skin flap
• Glabella/ nasion/ supraorbital ridge
  configuration used to anchor template for correct
  placement
• Outline of FS marked with a drill

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Computerised 3D reconstruction
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Model
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Model template
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Template in theatre
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FS outlined
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FS opened
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Our experience

• 8 patients to date
• Consistently accurate to within lt1mm of actual
  frontal sinus size
• Problem in chronic infection and with multiple
  previous procedures, bone may be difficult to
  differentiate from FS contents on CT, impacting
  on quality of model and thus template

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• Advantages
• CostltIGS model 100/20, template 25
• Maxfac lab at most regional hospitals
• Better anchoring than X ray
• 3D onlay template
• 3D model

Disadvantages Pre op planning Need specialist
facility Construction time (1 week) More
expensive than Caldwell X ray ?Accuracy
comparison with IGS further research
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Conclusion

• 3D models of frontal area generated from CT scans
  can be utilised to create 3D templates of the
  frontal sinus, which are then used intra-op as an
  onlay guide to frontal sinus mapping.
• Early experience shows them to be consistently
  accurate to within 1mm, suggesting they would be
  a useful adjunct to current techniques, esp if
  IGS not available.
• Comparison with existing techniques is needed.

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Thank you