Chapter 7 Anterior and Posterior Ethmoidal Arteries

10.1055/b-0037-143513

Chapter 7 Anterior and Posterior Ethmoidal Arteries

Humbert Massegur-Solench, Juan Ramón Gras-Cabrerizo, Elena Garcia-Garrigós, Joan M. Ademá-Alcover

Introduction

Anterior and posterior ethmoidal arteries (AEA and PEA) are branches of the ophthalmic artery, which traverses within the orbit from the internal carotid artery ( Fig. 7.1 ). The ethmoidal arteries pass between the oblique and medial rectus muscles heading to the roof of the ethmoidal sinus through the ethmoidal foramina traversing the lamina papyracea ( Figs. 7.2–7.4 ). The arteries run along the ethmoidal roof from lateral to medial, giving branches to supply the turbinates, the septum, and terminal branches intracranially ( Fig. 7.5 ). The most superior part of the basal lamella of the bulla ethmoidalis is the landmark to find the AEA because in most cases it is located behind its anterior wall. The computed tomography (CT) landmarks to find the AEA are the corticated break in the anterior lamina papyracea between the oblique and medial rectus muscles just behind the globe. The PEA crosses the ethmoid roof through a canal located anteriorly to the superior attachment of the anterior wall of the sphenoid sinus. Depending on the pneumatization, the bulging of the bony canal at the ethmoid roof is more evident for the anterior than for the PEA. The CT landmarks to find the posterior artery are more difficult to define except for a corticated sulcus in the skull base where the artery leaves the orbit. The knowledge of these arteries is crucial for endonasal procedures, such as endoscopic sinus surgery, endoscopic skull base surgery, orbit decompression, and epistaxis, bearing always in mind that the damage to them can produce a catastrophic orbital retrobulbar hemorrhage.1–5

**Fig. 7.1** CT scan with contrast (cadaver). Anterior ethmoidal arteries. Intraorbital and ethmoidal course. On the left side, the septal (*) and anterior meningeal branches (**) can be seen. AEA, anterior ethmoidal artery.

**Fig. 7.2** Coronal CT scan: sulcus of the anterior ethmoidal arteries through the anterior ethmoidal foramen.

**Fig. 7.3** Axial CT scan: anterior ethmoidal arteries crossing the anterior ethmoidal complex taking an oblique route from posterolateral to anteromedial.

**Fig. 7.4** Left anterior ethmoidal artery dissected from the orbit. The orbital fat has been removed to appreciate the origin from ophthalmic artery and the course between the superior oblique and medial rectus muscle. AEA, anterior ethmoidal artery; FS, frontal sinus; MRM, medial rectus muscle; OA, ophthalmic artery; SOM, superior oblique muscle.

**Fig. 7.5** Left anterior ethmoidal artery entering from the orbit through the anterior ethmoid foramen and giving the anterior meningeal artery. AEA, anterior ethmoidal artery; AMA: anterior meningeal artery; O, orbit.

7.1 Indications to Expose the Ethmoidal Arteries

In severe epistaxis not controlled by the ligature of the sphenopalatine artery, the AEA can be an additional source of bleeding and has to be localized.
Trauma with fracture of the nasofrontal complex or the skull base can produce bleeding of the ethmoidal arteries that may need to be coagulated or ligated.
The first step to approach an anterior skull base meningioma is to dissect and to coagulate both arteries bilaterally by bipolar diathermy, to improve bleeding control.
The AEA can be useful as a landmark to find the frontal recess, but the variation in its location and bulging on the ethmoid roof is not always safe. Thus, the basal lamella of the ethmoidal bulla is a better landmark.
The PEA can be a good landmark to find the optic nerve knowing that the distance between both is approximately 6 mm.
The anterior meningeal artery, branch of the anterior ethmoid artery, and the first olfactory fiber can be useful as landmarks to know the posterior limit of skull base exposure to perform the Draf III procedure.
Both arteries need to be identified as anterior and posterior limits for endoscopic orbital decompression.
Visualization of the ethmoidal arteries is important to avoid retrobulbar hemorrhage in endoscopic transnasal approaches in the treatment of medial and inferior orbital lesions.

7.2 Surgical Steps

After a gentle medialization of the middle turbinate, the uncinate process is identified and removed from its superior insertion to its horizontal aspect. The basal lamella of the bulla ethmoidales is then opened and removed ( Fig. 7.6 ). The AEA will be found behind the insertion of the basal lamella ( Fig. 7.7 ), which corresponds to the anterior wall of the ethmoidal bulla and not behind the frontal recess. The artery crosses the ethmoidal roof, taking an oblique route from the posteromedial break in the lamina papyracea to the lateral lamella of the cribriform plate ( Fig. 7.8 ). Depending on the pneumatization of the ethmoidal roof, the artery can be more or less evident; it can even have a mesentery suspended from the skull base. There is the possibility of a dehiscence inferiorly ( Fig. 7.8 ). In very few cases, the artery may be found anterior to the basal lamella ( Fig. 7.9 ).

**Fig. 7.6** Left nasal fossae. Bulla ethmoidalis with the basal lamella partially removed as the first step to localize the anterior ethmoidal artery. EB, ethmoid bulla; MT, middle turbinate.

**Fig. 7.7** Left nasal fossae. Anterior ethmoid roof after removal of the ethmoid bulla. Relationship of the anterior ethmoidal artery with the basal lamella of the ethmoidal bulla and frontal recess. AEA, anterior ethmoidal artery; BLBE, basal lamella of the bulla ethmoidalis; FS, frontal sinus.

**Fig. 7.8** Pneumatized left anterior ethmoidal roof with the oblique route of the anterior ethmoidal artery (partially dehiscent) from the posteromedial break in the lamina papyracea to the lateral lamella of the cribriform plate. The basal lamella of the ethmoidal bulla anterior to the artery and posterior to the frontal recess. AEA, anterior ethmoidal artery; BLBE, basal lamella of the bulla ethmoidalis; FR, frontal recess; LP, lamina papyracea.

**Fig. 7.9** Left anterior ethmoidal artery exposed just anterior to the basal lamella of ethmoidal bulla. AEA, anterior ethmoidal artery; BLBE, basal lamella of the bulla ethmoidalis.

The PEA enters the ethmoid roof from the orbit through the posterior ethmoidal canal embedded in the skull base and is thus less identifiable in the CT scan or during the dissection ( Figs. 7.10–7.12 ).

**Fig. 7.10** Coronal CT scan with contrast (cadaver). Posterior ethmoidal arteries. Intraorbital and ethmoid roof courses. PEA, posterior ethmoidal artery.

**Fig. 7.11** Coronal CT scan. Cortical sulcus of the posterior ethmoidal artery crossing the ethmoidal roof. PEA, posterior ethmoidal artery.

**Fig. 7.12** Left anterior and posterior ethmoidal arteries dissected from the orbit passing through the superior oblique muscle and medial rectus muscle. The orbital fat has been removed. AEA, anterior ethmoidal artery; MRM, middle rectus muscle; OA, ophthalmic artery; PEA, posterior ethmoidal artery; SOM, superior oblique muscle.

The next step is to open and remove the basal lamella of the middle turbinate and, following the slope of the skull base, to identify the anterior wall of the sphenoid sinus. The PEA crosses the ethmoidal roof in front of this wall ( Figs. 7.13–7.15 ). The identification of the sulcus of the artery may be used as a landmark to localize the optic canal. The distance between the artery and the nerve is about 6 mm ( Figs. 7.16 and 7.17 ). In case the pneumatization has originated a sphenoethmoidal cell (formerly known as Onodi cell), there is no wall between the PEA and the optic canal, but it can be also useful as landmark in this anatomic variation.

**Fig. 7.13** Left posterior ethmoidal artery and nerve crossing the ethmoidal roof just in front of the superior part of the anterior wall of the sphenoid sinus. AWSS, anterior wall of the sphenoid sinus; LP, lamina papyracea; PEA, posterior ethmoidal artery.

**Fig. 7.14** Left posterior ethmoidal artery and nerve. Relationship between the artery and the optical nerve after the removal of the anterior wall of sphenoid sinus. LP, lamina papyracea; OCR, opticocarotid recess; ON, optic nerve; PEA, posterior ethmoidal artery.

**Fig. 7.15** Course of the left posterior ethmoidal artery and nerve crossing the ethmoid roof from the sulcus in the posterior lamina papyracea to the cribriform plate. LP, lamina papyracea; PEA, posterior ethmoidal artery; PEN, posterior ethmoidal nerve.

**Fig. 7.16** Left posterior ethmoidal artery. Relationship between the artery, anterior wall of the sphenoid sinus, optic nerve, and carotid artery. AWSS, anterior wall of the sphenoid sinus (partially removed); ICA, internal carotid artery; OCR, opticocarotid recess; ON, optic nerve; PEA, posterior ethmoid artery.

**Fig. 7.17** Left ethmoidal roof after removal of the basal lamellas with anterior and posterior ethmoidal arteries crossing from the orbit to the cribriform plate. AEA, anterior ethmoidal artery; LP, lamina papyracea; PEA, posterior ethmoidal artery.

After the identification of both arteries, they can be dissected following their intraorbital course to the ophthalmic artery. The orbital fat must be removed to clearly distinguish the relationship between the arteries and the superior oblique muscle and medial rectus muscle ( Figs. 7.18–7.21 ). There are variations in the number and situation of the arteries: they can be absent in one or both sides, or a middle ethmoidal artery (a so-called “tertia”) can be found in around 30% ( Fig. 7.22 ).6

**Fig. 7.18** Global view of the anterior skull base bilaterally with anterior and posterior ethmoidal arteries crossing the ethmoidal roof and their relationship with the optic nerve, lamina papyracea, and cribriform plate. AEA, anterior ethmoidal artery; CP, cribriform plate; LP, lamina papyracea; ON, optic nerve; PEA, posterior ethmoidal artery.

**Fig. 7.19** Course of the anterior and posterior ethmoidal arteries from the ophthalmic artery to the cribriform plate crossing the ethmoidal roof. (The orbital fat has been removed and the medial rectus muscle rejected laterally.) AEA, anterior ethmoidal artery; ICA, internal carotid artery; MRM, medial rectus muscle; OA, ophthalmic artery; ON, optic nerve; PEA, posterior ethmoidal artery; SOM, superior oblique muscle.

**Fig. 7.20** Scheme of the anterior and posterior ethmoidal arteries showing the branches for the septum and lateral nasal wall.

**Fig. 7.21** Sagittal CT scan with contrast (cadaver) with anterior and posterior ethmoidal arteries in the nasal septum. AEA, anterior ethmoidal artery; PEA, posterior ethmoidal artery.

**Fig. 7.22** Multiple ethmoidal arteries in a left ethmoidal roof, as an anatomic variation. AEA, anterior ethmoidal artery; MEA, middle ethmoidal artery; PEA, posterior ethmoidal artery.

Through-cutting forceps, Kuhn-Bolger probes, and curved curettes are recommended as the best instruments for this approach. In special cases, it can be useful to employ a diamond burr to thin the skull base when a PEA is embedded in thick bone.