Fig. 1.1
Bony anatomy of the lacrimal sac fossa and medial orbital wall. The anterior and posterior lacrimal crests are formed by the maxillary and lacrimal bones, respectively
The medial orbital wall is formed, from anterior to posterior, by the:
Frontal process of the maxilla
Lacrimal bone
Ethmoid bone
Lesser wing of the sphenoid bone
The thinnest portion of the medial wall is the lamina papyracea, which covers the ethmoid sinuses laterally. The many bullae of ethmoid pneumatization appear as a honeycomb pattern medial to the ethmoid bone (Fig. 1.2). The medial wall becomes thicker posteriorly at the body of the sphenoid, and again anteriorly at the posterior lacrimal crest of the lacrimal bone.
Fig. 1.2
The ethmoidal air cells are medial to the removed lacrimal bone, and may extend anteriorly to pneumatize the maxillary bone of the lacrimal sac fossa
The frontoethmoidal suture is important in orbital bony decompression or lacrimal surgery as it marks the roof of the ethmoid sinus, or the fovea ethmoidalis. Bony dissection superior to this suture may expose cerebrospinal fluid and the dura of the cranial cavity. The anterior and posterior ethmoidal foramina, conveying branches of the ophthalmic artery and the nasociliary nerve, are located at the frontoethmoidal suture, approximately 24- and 36-mm posterior to the anterior lacrimal crest, respectively (Fig. 1.3) [19]. Piagkou et al. found high anatomic variation, however, with anywhere from 1 to 6 ethmoidal foramina present in 249 human orbit specimens, with 61 % having 2 foramina [20].
Fig. 1.3
Anteroposterior distances of the foramina from the anterior lacrimal crest. The ostium of the maxillary sinus lies approximately in a vertical line to the anterior ethmoidal foramen
The anterior lacrimal crest is an important landmark during external dacryocystorhinostomy surgery, as it represents the anterior border of the lacrimal sac fossa. In addition, the anterior limb of the medial canthal tendon attaches to the superior aspect of the anterior lacrimal crest. This attachment of the medial canthal tendon is often detached from the underlying bone along with the periosteum in order to gain better exposure during surgery.
A vertical suture runs centrally between the anterior and posterior lacrimal crests, representing the anastomosis of the maxillary bone to the lacrimal bone (see Fig. 1.1). A suture located more posteriorly within the fossa would indicate predominance of the maxillary bone, whereas a more anteriorly placed suture would indicate predominance of the lacrimal bone. The lacrimal bone at the lacrimal sac fossa has a mean thickness of 106 μm, which allows it to be easily penetrated to enter the nasal cavity at surgery [21]. In a patient with a maxillary bone dominant fossa, the thicker bone makes it more difficult to create the osteotomy. Twenty-five percent of Caucasian orbits are estimated to have a fossa that is equal parts maxillary and lacrimal bones, but up to a third may have a predominant maxillary bone [22].
At the confluence of the medial and inferior orbital rims, at the base of the anterior lacrimal crest, a small lacrimal tubercle may be palpated externally to guide the surgeon to the lacrimal sac located posterior and superior to it. In 28–34 % of orbits, the tubercle may project posteriorly as an anterior lacrimal spur [16, 23].
The nasolacrimal canal originates at the base of the lacrimal sac fossa, and is formed by the maxillary bone laterally and the lacrimal and inferior turbinate bones medially. The width of the superior opening of the canal measures, on average, 4–6 mm [16]. The duct courses posteriorly and laterally in the bone shared by the medial wall of the maxillary sinus and the lateral nasal wall for 12 mm, on average, to drain into the inferior meatus of the nasal cavity [24].
Nasal and Paranasal Sinuses
Knowledge of sinus anatomy enhances the understanding of surgical relationships to the orbit, and is particularly important in endonasal approaches. The bones forming the orbital floor, roof, and medial wall are pneumatized by air sinuses arising from the primitive nasal cavities. They retain communication with the nasal cavity and are thus lined by the nasal mucous membrane. The sinuses appear in early childhood, increase actively during puberty, and may continue to grow until 30 years of age [16].
The maxillary sinus is the largest of the paranasal sinuses, measuring 15 cm3 [16]. The roof of the maxillary sinus forms the orbital floor that declines from the medial wall to the lateral wall at an angle of approximately 30°. The maxillary sinus drains into the hiatus semilunaris within the middle meatus through an ostium located near the level of the orbital floor, immediately inferior to the central portion of the maxilloethmoidal orbital strut. The ostium measures, on average, 24 mm from the orbital rim, which is approximately in a vertical line to the anterior ethmoidal foramen in the medial orbital wall (see Fig. 1.3) [25].
The ethmoid sinuses are the first to develop, reaching adult configuration at as early as 12 years of age [26]. Ethmoid bullae are particularly exuberant in their expansion, and frequently extend past the suture of the ethmoid bone and even into the lacrimal and maxillary bones of the lacrimal sac fossa (see Fig. 1.2) [27, 28]. The ethmoid sinuses are shaped like a rectangular box, slightly wider posteriorly where they articulate with the sphenoid sinus. The ethmoid sinuses comprise three main groups of air cells:
Anterior—drain into the middle meatus
Middle—drain into the middle meatus
Posterior—drain into the superior meatus
The roof of the orbit slopes down as it travels medially, and this slope continues at the frontoethmoidal suture to become the roof of the ethmoid sinus, or fovea ethmoidalis. The ethmoid roof continues to slope inferiorly and medially to overlie the nasal cavity as the cribriform plate. The crista galli bisects the cribriform plate on its superior aspect, and continues inferiorly as the vertical nasal plate, or vomer. Because of this sloping, which is most prominent over the anterior ethmoid air cells, it is important to know the individual anatomy before surgery to avoid inadvertent cerebrospinal fluid leak or more severe intracranial injury [29].
The anatomic relationship of the anterior ethmoid air cells to the lacrimal sac fossa is important to understand before performing dacryocystorhinostomy in order to avoid confusion between the ethmoid and nasal cavities during creation of the ostium. A close anatomic relationship between the anterior ethmoid air cells, termed the agger nasi cells, to the lacrimal sac fossa has been demonstrated in several past studies [26–28, 30–33]. These agger nasi bullae may pneumatize the lacrimal bone, and rarely extend into the frontal process of the maxillary bone. A study by Whitnall in 1911 described the location of the anterior ethmoid air cells being:
directly medial to the lacrimal sac fossa in 86 % of skulls [27]
extending anteriorly to the vertical maxillary-lacrimal suture in 32 % of skulls
and extending farther to the anterior lacrimal crest in an additional 54 %
The ethmoid cells were located consistently in the superior half of the fossa, with the inferior half of the fossa directly adjacent to the middle meatus of the nasal cavity.
Similarly, Blaylock et al. reviewed computed tomography (CT) scans of 190 orbits and found that in 93 % of the orbits, the anterior ethmoid cells extended anterior to the posterior lacrimal crest, with 40 % extending anterior to the maxillary-lacrimal bone suture and entering the frontal process of the maxilla [28]. In only 7 % of orbits was the nasal cavity directly adjacent to the entire lacrimal sac fossa. As described by Whitnall, the anterior extension of the air cells was most prominent adjacent to the superior half of the lacrimal sac fossa [26–28, 30, 32, 34]. The ethmoid air cells and sinus mucosa should thus be removed to create a proper osteotomy.
Understanding the anatomic relationship of the lacrimal sac fossa to the ethmoid sinus also helps avoid complications such as inadvertent dacryocystorhinostomy fistulization into the ethmoid sinus, cerebrospinal fluid leakage, orbital hemorrhage, and trauma to subsequent scarring of the nasal mucosa and nasal septum [35].
Laterally, the nasal wall has three or more horizontal ridges termed turbinates, with a corresponding meatus below each (Fig. 1.4). The inferior turbinate is the largest, arising from the medial wall of the maxillary sinus. The smaller and more posterior middle, superior, and supreme (if present) turbinates are outcroppings of the ethmoid bone. The supreme turbinate may be found in up to 65 % of patients. The inferior turbinate is visualized by directing a nasal speculum parallel to the floor of the nasal cavity. The nasal vestibule is the large cartilaginous anterior dilatation of the nose above the nares, covered by squamous epithelium with hair follicles, to which the silicone tubes may be secured during surgery.
Fig. 1.4
Endonasal sagittal view. Each nasal turbinate has a corresponding meatal space located immediately below (FS frontal sinus, IT inferior turbinate, MT middle turbinate, NV nasal vestibule, S supreme turbinate, SS sphenoid sinus, ST superior turbinate)
The middle turbinate originates posteriorly from the roof of the nose at the cribriform plate, and arises anteriorly from the medial wall of the maxillary sinus. The lacrimal sac fossa lies anterior and lateral to the anterior tip of the middle turbinate, thus the entry in an external dacryocystorhinostomy is at the anterior tip of the middle turbinate (Fig. 1.5). An ostium achieved by the endoscopic approach is usually more inferior to the routine external site.
Fig. 1.5
Endonasal site of a dacryocystorhinostomy ostium. Transillumination through the lacrimal sac fossa demonstrates its location at the anterior tip of the middle turbinate (FS frontal sinus, IT inferior turbinate, MT middle turbinate, SS sphenoid sinus, ST superior turbinate)
Within the middle meatus lies a curvilinear gutter, the hiatus semilunaris, into which the ostium of the maxillary sinus drains. It is bordered inferiorly by a bony ridge termed the uncinate process, and superiorly by the bulla ethmoidalis prominence which represents the most anterior ethmoid air cells (Fig. 1.6) [36]. The ethmoid (anterior and middle), frontal, and maxillary sinuses empty into the middle meatus. The frontonasal duct drains the frontal sinus into the anterosuperior portion of the hiatus semilunaris.
Fig. 1.6
Endonasal view of lateral nasal wall with turbinates removed (BE bulla ethmoidalis, FS frontal sinus, HS hiatus semilunaris, IT inferior turbinate, MT middle turbinate, O-MS ostium of maxillary sinus, SS sphenoid sinus, UP uncinate process, * ethmoid ostia)
Secretory System
Lacrimal Gland and Accessory Glands
The primary lacrimal gland is located in the superotemporal orbit in a shallow lacrimal fossa of the frontal bone. The gland is composed of numerous acini (lobular clusters of secretory cells) that drain into progressively larger tubules and ducts. The acini are made up of a basal myoepithelial cell layer with inner columnar secretory cells. Contraction of the myoepithelial cells helps force secretions into the tubules and drainage ducts [37].
The gland measures 20 × 12 × 5 mm and is divided by the lateral horn of the levator aponeurosis into a larger orbital lobe, and a lesser palpebral lobe below [38, 39]. The size of the lacrimal gland decreases with age but does not vary by gender [40]. The orbital lobe is the larger of the two lobes and lies posterior to the orbital septum and preaponeurotic fat and anterior to the levator aponeurosis [38]. Two to six secretory ducts from the orbital lobe of the lacrimal gland pass through the palpebral lobe or along its fibrous capsule, joining with ducts from the palpebral lobe to form 6–12 tubules that empty into the superolateral conjunctival fornix 4–5 mm above the tarsus [37, 41].
Accessory lacrimal glands, located in the conjunctival fornices and along the superior tarsal border, are comprised of:
The lacrimal gland receives innervation from cranial nerves V and VII, as well as from the sympathetics of the superior cervical ganglion [43]. The lacrimal branch of the ophthalmic division of the trigeminal nerve carries sensory stimuli from the lacrimal gland. The lacrimal gland receives arterial supply from the lacrimal artery, with contributions from the recurrent meningeal artery and a branch of the infraorbital artery. The intraorbital venous drainage travels adjacent to the artery and drains into the superior ophthalmic vein.
Parasympathetic secretomotor innervation to the lacrimal gland is more complex. Parasympathetic secretomotor fibers originate in the lacrimal nucleus of the pons, and travel a long course within the nervus intermedius, the greater superficial petrosal nerve, deep petrosal nerve, and the vidian nerve to finally synapse in the pterygopalatine ganglion [34]. Postganglionic parasympathetic fibers leave the pterygopalatine ganglion via the pterygopalatine nerves to innervate the lacrimal gland [44, 45]. In addition, some fibers may join the zygomatic nerve as it branches from the maxillary division of the trigeminal nerve and enters the orbit through the inferior orbital fissure. Branches of the zygomatic nerve may ascend and enter the posterior surface of the lacrimal gland either alone or in combination with the lacrimal nerve [38]. However, an anatomic study by Ruskell in 2004 found that parasympathetic fibers traveled along a branch of the middle meningeal artery through the superior orbital fissure before joining the ophthalmic or lacrimal artery to supply the lacrimal gland [46]. This was in contrast to the traditional assumption that secretomotor nerves pass to the gland via the zygomatic and lacrimal nerves.
Sympathetic nerves enter with the lacrimal artery and along with parasympathetics in the zygomatic nerve. The zygomatic branch of the maxillary trigeminal nerve gives off the lacrimal branch before dividing into zygomaticotemporal and zygomaticofacial branches. This lacrimal branch anastomoses with the lacrimal nerve of the ophthalmic trigeminal nerve or travels along the periorbita to independently enter the gland at its posterolateral aspect.
Excretory System
Lacrimal Drainage System
The lacrimal excretory pathway begins at a 0.3-mm opening on each medial eyelid termed the punctum [16, 41]. Because of more rapid growth of the maxilla compared with the frontal bone during embryologic development, the lateral migration pulls the inferior canaliculus laterally, resulting in the lower eyelid punctum being located slightly lateral to the upper eyelid punctum [8]. The punctal opening widens into the ampulla, which is 2 mm in height and oriented perpendicular to the eyelid margin, before making a sharp turn into the canaliculi which run parallel to the eyelid margins. The canaliculi, measuring 8–10 mm in length and 0.5–1.0 mm in diameter, are lined with stratified squamous epithelium and surrounded by orbicularis muscle (Fig. 1.7).
Fig. 1.7
Approximate dimensions of the lacrimal excretory system (BE bulla ethmoidalis, IT inferior turbinate, MS maxillary sinus, MT middle turbinate)
The superior and inferior canaliculi merge into a common canaliculus before entering the nasolacrimal sac in more than 90 % of individuals [41, 47]. In a large study using digital subtraction dacryocystograms, the common canaliculus was present in 94 % of lacrimal drainage systems. The upper and lower canaliculi joined at the wall of the lacrimal sac without a common canaliculus in an additional 4 %, with only 2 % of systems having completely separate drainage of the upper and lower canaliculi into the lacrimal sac [48]. More recent studies of human cadaver lacrimal systems have found distinct orifices in anywhere from <1 % to as high as 10 % of specimens [49, 50]. The common internal punctum visualized within the lacrimal sac during dacryocystorhinostomy surgery should be free of any mucosal membrane or fibrous stricture for long-term surgical success.
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