Usually the anterior ethmoid artery can be located one cell behind the frontal recess. The size of this cell varies: it can be small, it can be large. This cell is called a supraorbital cell (it is often an extension of the su-prabullar recess) (Bolger and Mawn, 2001). The anterior ethmoid artery can often be seen on CT, particularly as it enters the orbit where it produces a fluted defect in the lamina papyracea. The more pneuma-tized the supraorbital recess is, the more vulnerable it is to damage (Fig. 12.16). Occasionally the ethmoid bulla attaches directly onto the skull base. In these patients, the anterior ethmoid artery lies within its roof and is one "undulation" behind the attachment of the anterior wall of the ethmoid bulla to the skull base. The anterior ethmoid artery lies above the level of the attachment of the anterior end of the middle turbinate to the skull base and it can be avoided by staying below this level. This is yet another reason for not instrumenting the frontal recess unless there are good reasons for doing so. However, if the frontal recess does require opening, it is best approached anteriorly, away from the anterior ethmoid artery if the landmarks are poor owing to previous surgery or bleeding. As the anterior ethmoid artery is sometimes dehiscent, it is wise not to grasp polyps in this area if you are unable to identify the anatomy clearly. If visibility is good and the ethmoid bulla has not previously been opened, then, after inspecting the CT scan to check for the presence and position of agger nasi/bulla frontalis cells, the frontal recess can be found by following the anterior wall of the ethmoid bulla superiorly.
The anterior ethmoid artery is dehiscent at some point in the majority of patients (Lang, 1989). It is important to avoid damaging it; while tearing it can cause marked bleeding, the main concern is that if it is transected and it retracts back into the orbit, this can cause a marked increase in the pressure in the posterior compartment of the eye and place the retinal artery and its supply to the retina at risk. If it is torn, gentle bipolar diathermy will arrest the bleeding, but do this with great care in order to avoid transecting it by burning the remaining segment of the artery.
If there is significant bleeding into the posterior compartment of the eye, the eye will proptose, the orbit will become very firm, and after a few minutes the swinging flashlight test will reveal an afferent defect. A patient who is awake will mention discomfort and a loss of vision. If this is recognized immediately, an orbital tourniquet should be tried. This involves placing cotton wool over the closed eyelid and applying an orbital tourniquet (the ophthalmological equivalent of a sphygmomanometer) over the cotton wool and around the head, and then inflating it to systolic pressure. This should be done for one minute and then
it should be removed and the pupil reflexes and/or the vision checked. If the vision or pupil reflex has improved, the optical tourniquet should be reapplied and the process repeated every minute for up to 5 minutes. If this is done soon after the injury, it may be sufficient to stop bleeding into the orbit and it can arrest the process.
It is wise to monitor the vision for 6 hours afterwards to ensure that no further bleeding into the posterior compartment occurs. If this maneuver is not possible or does not work, the orbit must be decompressed. It is the authors' preference to do a lateral canthotomy and inferior cantholysis as this is both quick and efficient and is associated with minimum morbidity (Fig. 12.17). While some evidence suggests that the optic nerve can withstand ischemia for up to one hour, it is best to decompress the orbit as early as possible (Jones, 1997). You should not wait for an oph-thalmological colleague to arrive unless they will do so well within one hour. Assessing the vascular supply of the retinal vessels with an ophthalmoscope is inadequate and should not be relied upon.
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