Surgical Technique

The surgeon must have a good reason for operating in this area. The landmarks that will help you are the remains of the uncinate process, the remainder of the anterior wall of the ethmoid bulla, and a knowledge of the air cells from the CT scan.

Follow the superior remnant of the uncinate process upward with a 45° through-cutting forceps. Now is the time to change to a 45° endoscope to examine the area and obtain an overview. Uncapped agger nasi cells, the terminal recess, and the ethmoid bulla form domes that are joined together. It often appears that this is all there is and they might fool you into thinking that one of them is a small frontal sinus. Careful palpation, not prodding, with a ball probe next to the middle turbinate will reveal a crevice between the middle turbinate and the uncapped cells (Fig. 5.58a-o). The aim is to open this crevice, which will turn out to be the pathway to

Sagittal Skull Disection
Fig. 5.58 a A sagittal section showing multiple air cells along the skull base; their variety is endless. b-o Sequential dissection of an agger nasi air cell using submucosal dissection with a

the frontal recess and the frontal sinus, by "deflating" the cells. This is best done by passing the ball probe well above their domes and gently lateralizing them. The shaft of a Kuhn curette also works well. If visibility is good, it may be possible to do this by submucosal dissection. Fragments of bone should then be removed, taking care not to grab the mucosa as you want to leave the whole circumference of mucosa in order to avoid stenosis. If the bone is thick, then the end of a Kuhn curette is ideal for this maneuver. These domes are sequentially uncapped to reveal the next tier (Figs. 5.59a-j, 5.60a, b).

Kuhn Curette
ball probe. This strategy "deflates" these air cells to help open up access to the frontal recess. Fig.5.58f-o >
Anterior Wall The Ethmoid Bulla

The deflated mucosa is then draped over the lateral nasal wall. You can tell whether you have removed the most anterior cells by feeling the beak of the frontal bone with the Kuhn curette, as it is extremely thick. By uncapping of the remnant of the ethmoid bulla, the su-prabullar recess is exposed and this often contains the

Frontal Recess Cells

anterior ethmoidal artery and in front of it a supraorbital cell if one is present. The suprabullar cell lies behind the frontal recess and can easily be mistaken for it. Once this is completed, you have done a type II frontal sinusotomy. You should now ask yourself whether you have opened the frontal recess. You can confirm that you have by:

• A ball probe, a Kuhn curette, or a curved sucker passing freely high up into the frontal sinus.

• Registering the angle and length of this ball probe on the maxillary spine and repositioning it external to the nose.

• Transillumination, with the endoscope high up in the frontal recess.

• Seeing the convex posterior wall of the frontal sinus along with the spacious cavern of the sinus.

In order to make sure that you have entered the frontal recess and are into the frontal sinus, grip the shaft of the ball probe between the thumb and the index finger next to the nasal spine, noting the angle of the instrument at the same time. The instrument is then withdrawn and placed alongside the outside of the nose, placing it at the same angle with the pinch grip placed alongside the nasal spine. If the end of the ball probe is then higher than the eyebrow line, it is likely that the instrument is in the frontal sinus. If it is around or just above the medial canthus, then it is likely that the ball probe is not within the frontal recess but is within an agger nasi air cell. If the handle of the ball probe is noted to have been turned laterally when the instrument is passed up what is thought to be the frontal recess, then it may have been channeled in this direction by a bulla frontalis or a supraorbital cell (Fig. 5.61 a-c).

The partition between the bulla frontalis and the frontal recess is best resected with through-cutting forceps as high as the instruments will allow. The same applies to supraorbital cells that encroach and extend up the posterior wall of the frontal sinus.

Probing Surgical Procedure For Sinus

Fig. 5.59a, b Is the cell with a question mark the frontal has been pushed medially by the air cells, e-j A Khun-Bolger sinus? c, d A close-up view shows a sound locating a fine chan- curette is used to remove the roof of the second tier of cells, nel adjacent to the middle turbinate. It is as though the channel which then creates wide drainage for the frontal sinus.

Fig. 5.59a, b Is the cell with a question mark the frontal has been pushed medially by the air cells, e-j A Khun-Bolger sinus? c, d A close-up view shows a sound locating a fine chan- curette is used to remove the roof of the second tier of cells, nel adjacent to the middle turbinate. It is as though the channel which then creates wide drainage for the frontal sinus.

Suprabullar Cells

If there is poor visibility because of bleeding or polyps, this is an area in which not to go blindly prodding around. Rather, it is best to use local vasoconstrictors and to return once visibility has improved.

When operating in the frontal recess, the following guidelines may be helpful:

• Work out the anatomy before you operate. Reconstruct a three-dimensional image in your mind of the anatomy and insertion of the uncinate process, the position of agger nasi air cells, whether there is a bulla frontalis or supraorbital cell, and the position and shape of air cells in and around the frontal recess. This is your map and you do not want to be lost in the wilderness! (Fig. 5.62a-f).

• It is vital not to prod medially as you pass any instrument into the frontal recess, as the lateral lamella is usually the thinnest part of the skull base and it is easy to cause a CSF leak in this area.

• It is important not to palpate laterally in the frontal recess if there are small or no agger nasi air cells, as you can enter the orbit here. Check carefully on the CT image and ask the assistant to ballotte the eye while you are examining this area to make sure that you are not going to enter the orbit. Where there is doubt about where you are, it is safer to stay anterior, just behind the "beak" of the frontal bone. The bone is very thick anteriorly and if you approach the frontal recess staying just lateral to a sagittal plane, in line with the attachment of the middle turbinate to the skull base, you are less likely to traverse dura.

• The anterior wall of the ethmoid bulla is a good landmark in finding the frontal recess as its anterior wall will lead you up to the frontal recess. It also "guards" the anterior ethmoid artery if it is attached to the skull base, and when this happens the artery is often in the next undulation in the roof of the ethmoid bulla. 6, 7, 8

You should not go searching for the anterior ethmoid artery as it is not a useful landmark and to do so is dangerous. It is important to be aware that it is partially dehiscent in 20% of patients. If the skull base is very well pneumatized, the artery can even be free like a tightrope, especially if there is a large supraorbital cell. (See Fig. 5.63 a-g.)

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Responses

  • leone
    What is the difference between a double ended ball probe and a kuhn probe?
    8 years ago

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