The Nasolacrimal System and Dacryocystorhinostomy

In select cases, an endoscopic dacryocystorhinostomy may be indicated when epiphora is due to nasolacrimal duct obstruction.1–6 The nasolacrimal sac is found anterior to the most anterior attachment of the middle turbinate in the lateral nasal wall.7,8 The sac is bounded anteriorly by the frontal process of the maxilla and posteriorly by the lacrimal bone. A line drawn anteriorly from the anterior attachment of the middle turbinate bisects approximately the inferior one third of the lacrimal sac (Fig. 6.2A,B). The nasolacrimal duct courses slightly diagonal and parallel to the uncinate process in a posteroinferior direction toward the inferior meatus. The nasolacrimal duct may be divided into two parts: 1) a bony (or intraosseous) nasolacrimal duct (12 mm); 2) a membranous nasolacrimal duct (5 mm). The intraosseous portion has a bony wall circumferentially and is typically identified as a prominent convexity in the lateral wall of the nose running adjacent to the anterior middle meatal margin. The bony wall may be very thin posteriorly, adjacent to the uncinate process or maxillary natural ostium. Superiorly, the lacrimal sac receives the opening of the common canaliculus; the common outflow tract into the nose from the superior and inferior canaliculus (Fig. 6.3A,B).

The membranous nasolacrimal duct is located in the inferior meatus and consists of a membranous medial wall and a bony lateral wall. The membranous medial wall collapses into the lumen and functions as a one-way valve (Hasner’s valve) to minimize retrograde flow of secretions or air into the nasolacrimal duct and sac. Hasner’s valve may be seen traversing the anterior third of inferior meatal wall. With a small probe, a mucosal canal or trench can be followed superiorly to identify Hasner’s valve and the lacrimal ostium (Fig. 6.4). Occasionally, Hasner’s valve is absent. In these cases a patulous opening looking into the bony nasolacrimal duct may be seen in the superior recess of the inferior meatus adjacent to the inferior turbinate lamellar insertion into the lateral nasal wall (Fig. 6.5).

Anterior and Posterior Ethmoid Arteries

Endoscopic ligation or cauterization of the anterior ethmoid artery has been advocated in select cases with anterior epistaxis.9,10 The anterior and posterior ethmoid arteries are branches of the ophthalmic artery which arises from the internal carotid artery and enters the orbit via the optic foramen, together with the optic nerve. The ophthalmic artery then runs on the medial wall of the orbit beneath the lower border of the superior oblique muscle. The artery gives off both the anterior and posterior ethmoid arteries, which can be seen penetrating the periorbita into their respective bony canals, coursing through the roof of the ethmoid sinus.11 Occasionally, the anterior ethmoid artery courses within a mucosal fold up to several millimeters below the level of the bony ethmoid roof. Additionally, branching of these arteries may occur within the ethmoid roof. The ethmoid arteries then enter the cranial cavity medially, in the anterior and posterior to the cribriform plate area, respectively. Both arteries give off a meningeal branch to the dura as they enter intracranially (Fig. 6.6A,B).

Orbital Decompression

Orbital decompression may be indicated for a patient with an orbital abscess, periorbital or orbital hematoma, or severe Graves’ ophthalmopathy with exposure keratitis and threatened visual loss.12–22 When a subperiosteal abscess is present, only the lamina papyracea needs partial or complete removal to ensure adequate drainage of the abscess loculations into the nose. This may require exposing the periorbita over the superomedial or inferomedial orbital walls to ensure adequate drainage of all potential abscess loculations. Nasal packing is usually avoided. The periorbita is left intact without any incisions (Fig. 6.7A,B).

For patients with Graves’ ophthalmopathy, the lamina papyracea and MOF are removed medial to the infraorbital nerve through a wide antrostomy. Postoperative diplopia is possible, but may be minimized by preserving the horizontal ridge of the antrostomy, and placing the periorbital incisions parallel to the superior and inferior borders of the medial rectus muscle (see above), at its junction with the superior oblique and inferior rectus muscle, respectively.23 The periorbita is incised to allow herniation of orbital fat into the ethmoid and maxillary sinus cavities, while minimizing significant muscular herniation of the medial rectus especially (Fig. 6.8A,B). Medial and inferior orbital decompression allows for ~4–5 mm proptosis reduction. This may have to be combined with a lateral orbital decompression through an external approach. Care is taken not to occlude the maxillary, frontal, or sphenoid ostia with orbital fat, as this may result in secondary ostial obstruction and rhinosinusitis.24,25 In these situations an extended middle meatal, frontal, and/or sphenoid sinusotomy may be prudent.

Optic Nerve Decompression

In patients with worsening visual acuity due to traumatic neuropathy or neoplastic compression, an optic nerve decompression may be indicated.26–29 The orbital apex may be found by following a vertical line, parallel and at the coronal plane of the superior vertical ridge of the antrostomy and adjacent posterior wall of the maxillary sinus, toward the junction of the posterior ethmoid sinus roof with the superomedial orbital wall. The orbital apex is located ~7 cm from the columella. The canalicular portion of the optic nerve is identified as it takes an abrupt turn medially at this point, coursing toward the optic chiasm (Fig. 6.9). The thicker bone in this area is carefully thinned with a diamond bur and removed with a periosteal elevator. In the cadaver laboratory this can be carefully performed utilizing a bone curette. The length of the canalicular portion is ~8–12 mm. The optic nerve sheath is continuous with the dura mater in this area (Fig. 6.10). Incision of this thick sheath reveals the optic nerve. The space around the nerve is continuous with the subdural space and results in a CSF leak if left open to the nasal cavity. Therefore, if the optic nerve sheath is opened, one must be prepared to close the CSF leak (Fig. 6.11).

Sphenoid Sinus Lateral Wall, Internal Carotid Artery, and Adjacent Neurovascular Structures

The course of the internal carotid artery (ICA) within the lateral sphenoid sinus wall has been endoscopically highlighted.30 Appropriate understanding of this course is important when considering extended endoscopic access to the petrous apex, retroclival region or to the cavernous sinus (Fig. 6.12).

The sphenoid ICA is dividable into six segments: anterior clinoid, intracavernous, parasellar, paraclival, 2nd genu, and petrous segments. The paraclival ICA starts at the supralacerum or 2nd genu segment. The 2nd genu of the ICA can be located by drilling along the vidian canal; the latter pointing to the anterolateral aspect of the genu. From here, the ICA ascends along the side of the clivus, in front of the petrous apex, and then enters the cavernous sinus, medial to the branching of the trigeminal ganglion. The parasellar, intracavernous, and anterior clinoid segments of the ICA, form a C-shaped curve, with its convexity directed ante-riorly. The inferior horizontal segment of this curve starts as the paraseller ICA bends anteriorly at a variable angle to run horizontally forward and slightly upwards. The ICA then bends superiorly as the anterior vertical limb of the “C” as the intra-cavernous segment. The artery then bends posteriorly again exiting the cavernous sinus and forming the superior horizontal segment that runs medial to the anterior clinoid process (anterior clinoid segment), and then enters the subarachnoid space intracranially. The anterior clinoid segment of the ICA runs immediately inferior to the canalicular portion of the optic nerve as it courses intracranially, creating a small triangular recess (opticocarotid recess) (Fig. 6.13).

In some patients with a well-pneumatized sphenoid, the carotid projects into the lumen of the sphenoid and is prone to inadvertent injury if one enters too far laterally through the posterior wall of the posterior ethmoid sinus. For this reason the sphenoid is generally entered medially adjacent to the septum, as previously described in Chapter 5 (sphenoid sinosotomy section).

Sphenopalatine Foramen, Pterygomaxillary Fossa, and Vidian Canal

Identification of the sphenopalatine foramen and pterygomaxillary fossa may be indicated in cases when posterior epistaxis requires endoscopic cauterization, or ligation, of the sphenopalatine or internal maxillary vessels.31–33 Exposure and control of these vessels may also be necessary during an endoscopic resection of a juvenile angiofibroma or other nasopharyngeal/pterygomaxillary space neoplasm.34–37

The sphenopalatine foramen is circular or oval, and is usually found in the posterior part of the superior meatus, a few millimeters above the tail of the middle turbinate. The foramen is formed when the sphenopalatine notch is closed superiorly against the lower surface of the body of the sphenoid. The notch itself is formed anteriorly by the orbital process of the palatine bone, inferiorly by the upper edge of the vertical plate of the palatine bone, and posteriorly by the sphenoid process of the same bone. A small bony ridge, the ethmoid crest, usually points to the sphenopalatine foramen, with the latter laying either completely or partially above the crest (class I and II respectively). Occasionally, the sphenopalatine foramen consists of two separate openings, a larger superior opening and a small inferior one (class III) (Fig. 6.15).38 Generally, the sphenopalatine artery divides into two or more branches before exiting through the sphenopalatine foramen. These branches are the posterior lateral nasal artery, usually emerging at the anteroinferior compartment of the sphenopalatine foramen, and the posterior nasal septal artery which courses medially toward the posterior nasal septum just inferior to the ostium of the sphenoid sinus and the tail of the superior turbinate. This branch is often transected in the course of a sphenoid sinusotomy and requires cauterization (Fig. 6.16).

The vidian nerve carries parasympathetic fibers to the nose and paranasal sinuses. The vidian nerve is found coursing along the floor of the lateral sphenoid sinus in a posteroanterior direction. The easiest way to visualize the nerve is to expose the spheno-palatine foramen first. A wide sphenoid sinusotomy is then performed to determine the level of the sphenoid floor. The vidian foramen may be found along the inferior bony face of the sphenoid immediately posterior and perpendicular to the sphenopalatine foramen. A small canal holding the pharyngeal or palatovaginal artery may also be tracked just medial to the vidian canal. The latter artery usually arises from the sphenopalatine artery within the pterygomaxillary fossa. The palatine bone and posterior maxillary sinus bony wall is removed to expose these pterygopalatine fossa structures (Fig. 6.17).

The pterygopalatine fossa can be exposed by removing the vertical ridge of the antrostomy and adjacent thin posterior bony wall of the maxillary sinus through the middle meatal antrostomy. For more extensive exposure, the inferior turbinate can be removed and the middle meatal antrostomy extended into the inferior meatus (extended maxillary antrostomy). This is discussed in the next section. The internal maxillary artery and its branches, the sympathetic and parasympathetic nerve plexus, veins, and buccal fat can be seen within the pterygopalatine fossa. Superiorly, the infraorbital nerve may be seen coursing toward the foramen rotundum superolateral to the vidian foramen (Fig. 6.18).39 Further dissection posterolateral to the base of the pterygoid process or plate exposes the infratemporal fossa with the foramen ovale (V₃ branch of the trigeminal nerve) and the foramen spinosum (middle meningeal artery) (Fig. 6.19).