CT scan-generated frontal sinus templates in osteoplastic

flap surgery

Mat Daniel, Jason Watson *, Anshul Sama

Otorhinolaryngology and *Maxillofacial Surgery

Nottingham University Hospital

British Rhinological Society

May 2008

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)

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

Aim

Develop a 3D template of the frontal sinus

that can be used intra-operatively as an

onlay guide to FS mapping

Model & Template productionImport CT images,

identify required region

Drill FS on light-cure sheetto form custom template

“Print” 3D sinus modellayer by layer

Onlay malleable light-cureresin sheet and process

Sterilise for directuse in theatre

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

Computerised 3D reconstruction

Model

Model + template

Template in theatre

FS outlined

FS opened

Our experience

8 patients to date

Consistently accurate to within <1mm 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

Advantages

Cost<IGS: model £100/£20, template £25Maxfac lab at most regional hospitals

Better anchoring than X ray

3D onlay template3D model

Disadvantages

Pre op planningNeed specialist facility

Construction time (1 week)

More expensive than Caldwell X ray

?Accuracy comparison with IGS: further research

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.

Thank you