1 Introduction top
Severe injuries to the anterior and/or posterior table of the frontal sinus may render the sinus non functional. In this situation, frontal sinus obliteration may be required. This involves exposure of the entire sinus, fastidious removal of all sinus mucosa and obliteration of the sinus cavity with autologous tissue.
2 Choice of tissue top
Many different autologous materials have been used for sinus obliteration. These include:
- Abdominal fat
- Spontaneous osteoneogenesis
Regardless of what other material will be used to fill the sinus, fascia will generally be the graft of choice for plugging the recess. Some surgeons add additional fascia to fill the sinus.
Abdominal fat is readily available and the graft harvest results in low morbidity. This material has a long and successful track record in the otolaryngology literature.
Nonvascularized muscle can also be used successfully to obliterate the sinus cavity. The morbidity of harvesting muscle is often greater than abdominal fat.
A pericranial flap can be used to obliterate small to medium size sinuses.
It has the advantage of being a vascularized flap. When using an osteoplastic bone flap, the bone flap may compress the blood supply to the pericranial flap thereby devascularizing it.
The pericranial flap must be inserted over the orbital rims and into the sinus. The reduced anterior table bone fragments must not strangulate the flap as it enters the sinus. A small bone defect (2-3 mm) must be generated to allow passage of the flap into the sinus.
The mucosa is stripped, the recess is plugged, and the sinus is left empty.
Cortical and cancellous bone can be harvested from the previously exposed skull (coronal approach) with minimal morbidity.
Large sinuses can be more challenging to fill with bone.
3 Exposure topenlarge
While elevating the coronal flap, it is important to maintain the integrity of the pericranial flap whenever possible. This flap may be used for obliteration of the sinus when the posterior table is intact. It is however most critical to maintain the pericranial flap integrity when posterior table fractures are present and there is greater probability of a dural tear. In these cases the pericranial flap will be used to repair the dura and reline the anterior cranial fossa.
Pearl: identification of explanted bone fragments
Final orientation of any removed bone fragments can be challenging. Placing the explanted segments on a rough sketch of the skull made with a sterile pen will maintain orientation until re-implantation. Outline each segment and the overall shape of the defect.
The bone fragments should be kept moist until they are re-placed.
4 Defining the sinus margin topenlarge
The margins of the frontal sinus are irregular and may not be visible through the fracture.
It is however critical to determine the precise margins of the sinus to allow for an accurate osteotomy and complete exposure of the sinus. There are several ways to accomplish this:
- Bayonet forceps
- 6-foot (1.83 m) Caldwell x-ray with coin reference
- Intraoperative navigation
One tine of the bayonet forceps (or bipolar cautery) can be inserted into the defect. The other tine spans the anterior table. The internal tine is then “walked” around the periphery of the sinus. The external tine is then used to guide markings which will outline the periphery of the sinus on the outer table bone. The outline can be marked with ink or electrocautery (the electrocautery should be placed at a low setting to coagulate overlying blood and avoid excessive bone injury).
Alternatively, a light source (such as an endoscope) can be inserted through the anterior table bone defect. The light will transilluminate the sinus and delineate its margins.
Beware of pitfalls such as soft-tissue and blood present in the sinus.
6-foot (1.83 m) Caldwell x-ray with coin reference
A 6-foot (1.83 m) Caldwell x-ray with (anterior-posterior Caldwell x-ray with the patient placed 6 feet from the x-ray tube) can be used to delineate the margins of the sinus. The 6-foot penny Caldwell generates a “life-size” representation of the sinus cavity. It is imperative that the orientation (ie, right and left) is clearly documented on the x-ray.
Scissors are then used to cut along the margins of the sinus. Lateral “wings” that project along the orbital rims are also cut out to help with orientation. A second copy of the sinus template is generated from the first in case one is contaminated during the procedure. An “R” is scratched into the right side of both templates to record orientation. Both copies are sterilized and brought onto the surgical field.
The template is then placed over the sinus using the orbital rim “wings” to help with orientation. The template is held in place. The sinus periphery can then be outlined using ink or electrocautery as previously described.
Intraoperative navigation can be used to outline the periphery of the sinuses using the preoperative CT scan. A reference array must be fixed to the skull (or Mayfield head holder) to allow for accurate navigation.
The navigation system is used to guide the probe along the periphery of the sinus.
Ink or electrocautery can be used to mark the outline.
5 Osteotomy topenlarge
After the proposed osteotomy has been marked at the periphery of the sinus, thin plates are applied spanning the sinus margin. An adequate number of plates should be applied to provide stability when the anterior table segment is osteotomized. The plates should be pre-applied prior to the osteotomy. This allows for accurate repositioning of the anterior table bone.
Each plate should be rotated away from the proposed osteotomy line. This can be accomplished by removal all but one screw located on stable bone outside the sinus. The plate can then be rotated away from the sinus.
Perforating the anterior table
A sagittal saw can be used to perform the osteotomy. However, a side-cutting burr (as illustrated) is more controlled and accurate. The bit is used to drill sequential holes along the superior border of the sinus. Individual holes are separated by several millimeters.
The handpiece should be angled approximately 45° towards the sinus and away from the cranial vault to avoid violation of the posterior table.
Completion of superior osteotomy
The holes are then connected to create a single osteotomy on the superior margin of the sinus.
Osteotomizing the orbital rims/glabella
Next, the drill is used to osteotomize the orbital rims and glabella in a similar fashion. Care should be taken to protect the orbital contents and supratrochlear/supraorbital neurovascular pedicles.
Intersinus septum osteotomy
If the intersinus septum is intact, it may be necessary to insert a curved osteotome through the superior osteotomy site and fracture the intersinus septum just deep to the anterior table bone. Care must be used to avoid injuring the posterior table.
A curved osteotome is then inserted through the superior osteotomy to cantilever the anterior table and generate a controlled fracture of any remaining attached bone. A clamp should be used to control the anterior bone fragment as the osteotomy fracture is completed.
6 Mucosa removal topenlarge
The sinus cavity is then suctioned free of any blood or mucous. An elevator and/or forceps are used to remove the sinus mucosa.
Diamond burrs of various sizes (1-6 mm) are then used to meticulously remove the sinus mucosa and a thin layer of bone from the entire sinus surface. All septations are drilled down to generate a single smooth sinus cavity.
Particular attention must be paid to the scalloped areas at the periphery of the sinus. In the supraorbital region this can be challenging. Extra time should be spent to assure that mucosa is removed from this area.
Rarely, a small amount of bone from the orbital roof may be removed to gain access to the deepest portions of the sinus.
A clamp is used to stabilize the free anterior bone segment(s) that were previously removed. A large diamond burr is then used to remove the mucosa from the inner surface.
When posterior table fractures are present, caution must be used when the sinus mucosa is removed. Aggressive manipulation of the dura can result in an iatrogenic CSF leak.
If defects in the posterior table approach 25% of the entire surface area, cranialization of the sinus should be performed. Click here for a description of cranialization.
Special attention should be given to mucosal removal along the posterior table fracture. A larger burr will reduce the risk of inadvertent intercranium penetration. The surgeon must assure that there is no mucosa entrapped along the fracture line.
7 Closure of the outflow tract topenlarge
An elevator is then used to circumferentially elevate the mucosa in the frontal recess bilaterally. The mucosa is then inverted and pushed inferiorly to obstruct the outflow tract. Free fascia is used for obliteration of the outflow tract.
Alternatively, a sharp 1-2 cm straight osteotome can be used to harvest a thin layer of outer layer calvarial bone. If the graft can be harvested from a region with Intact periosteum, this will help maintain the integrity of the graft.
Each bone graft is trimmed to fit into the frontal sinus infundibulum using a fine bone rongeur. The graft is then wedged into place to obstruct the sinus outflow tract.
8 Sinus obliteration topenlarge
Fat can be readily harvested from the abdomen. An incision can be placed around the umbilicus (better cosmesis) or in the left lower quadrant.
To maintain maximum graft viability, one adequately sized piece should be obtained without the use of electrocautery.
The fat graft is then placed in the sinus cavity and ...
... distributed to fill the entire defect.
The anterior surface should be trimmed so that the fat does not extrude from the osteotomy gap.
The anterior table bone fragments are then repositioned and the pre-applied plates are rotated back into position to fixate the fragments. Replace any remaining fragments and fix them with small plates.
This clinical photograph shows the fixation.