Fig. 5.1
(a) Anterior nasal space, lateral nasal space, and ethmoid and frontal sinuses. The middle turbinate is removed. (cadaver, 89-year-old male). (b) Web-like structure seen from the inferior aspect. (cadaver, 89-year-old male). (c) Pin piercing the base of the ala nasi. (cadaver, 89-year-old male). (d) Pin emerged at the superior border of the nasal vestibule. The nasolacrimal canal is directed posteriorly. (cadaver, 89-year-old male)
The choanae, the round, larger posterior nares, are the spaces representing the posterior limits of the nasal cavities and divide the nose from the superior epipharynx (Fig. 5.2a, b). The choanae are clearly visible from the front using nasal endoscopy (Fig. 5.2a). The floor of the nasal cavity is bordered by the hard and soft palates (Fig. 5.3) [1].
Fig. 5.2
(a) Appearance of the choanae seen from the front. (cadaver, 97-year-old female). (b) Appearance of the choanae seen from the back. (cadaver, 97-year-old female)
Fig. 5.3
Appearance of the facial half including the nasal septum. (cadaver, 89-year-old male)
The lateral wall of the nose is a complex structure [1]. There are three or four paired nasal turbinates with a corresponding meatus under each turbinate (Fig. 5.4) [1]. The most important paranasal structures are concentrated in the middle meatus, and the nasolacrimal duct empties into the inferior meatus [1–3].
Fig. 5.4
Appearance of the lateral nasal wall with surrounding structures. (cadaver, 89-year-old male)
The effect of the nasal conchae and meatuses on the inspired airstream sets the parameters for nasal breathing and treatment of air before it is directed down into the lungs [4]. The turbulent airflow caused by the conchae adds to the perceived resistance of nasal airflow and the sensation of adequate breathing [4]. Turbulent airflow allows for the wafting of molecules to the sensory cells of the olfactory system, aiding the senses of taste and smell [4].
The external proportions of the nose are expected to influence the internal anatomy, and thus cause differences in nasal physiology. Populations adapted to cold and dry environments tend to have large, protruding external noses, downwardly directed nostrils, and narrower skeletal nasal apertures [5]. These characteristics are thought to induce turbulence of nasal airflow, thereby maximizing filtration, heat, and humidification of air within the nasal passages [5–7]. Conversely, those with smaller, flatter external noses, more anteriorly directed nares, and shorter piriform apertures are better adapted to hot, humid environments. Because much of the energy required for breathing is expended in the nasal passages, a broader, flatter nasal structure favors less turbulent airflow, which is physiologically more economical because of the lower nasal airway resistance. In the platyrrhine nose, inspiratory airstreams passing through more horizontally placed nostrils are directed toward the inferior portion of the nasal chamber to condition very warm air, and the region anterior to the turbinates typically plays a lesser role in black than in white individuals [5, 8].
Nasal Septum
The nasal septum comprises cartilage anteriorly (quadrilateral/septal cartilage) and bone posteriorly (vertical plate of the ethmoid bone posterosuperiorly and vomer bone posteroinferiorly) (Fig. 5.5) [1]. A membranous columella that divides the nares is present in the anteroinferior area [9], and the vomerine cartilage occupies the posteroinferior area [10]. The nasal septum divides the nasal cavity into two portions and forms most of the nasal bridge [2].
Fig. 5.5
Appearance of the nasal septum and mucosa. The septal mucosa has been placed inside out. (cadaver, 89-year-old male)
Although the vertical plate of the ethmoid bone and the nasal septum comprise hyaline cartilage in neonates, the vomer is already a bone [10]. From 1 or 2 months after birth, the hyaline cartilage begins to ossify posteriorly and forms the vertical plate of the ethmoid bone [10]. The nasal septum begins to grow rapidly from puberty and raises the external nose [10]. With its growth, the cartilage occasionally bends, forming protuberances and spurs at the junction with the vomer [3, 10]. Approximately 90 % of adults show variable extents of septal bending that is directed both anteroposteriorly and transversely [3]. The nasal septum and bone continue to grow until the end of puberty [10]. The posterior edge of the cartilage grows posteriorly from puberty, resulting in formation of the sphenoid or vomerine processes [10].
The septal mucosa is thickest centrally in the superoinferior direction with a tendency to be thicker anteriorly in the anteroposterior direction (Fig. 5.5) [10]. The mucosa of the olfactory cleavage is comparatively thin [10]. Kiesselbach’s area, a common site of nasal bleeding, is situated in the anteroinferior part of the septal mucosa [10].
Clinical Correlations
1.
Nasal septal surgery should be performed after puberty because removal of the septal cartilage before puberty may prevent growth of the external nose [10]. For the same reason, it should be avoided or a minimal focal septoplasty should be done, if greatly needed in pediatric DCR.
2.
Excessive removal of the anteriorly located septal cartilage occasionally causes ptosis of the nasal tip [10]. A saddle nose may occur by overharvesting the septal cartilage in the dorsum nasi [10]. Therefore, a 5- to 10-mm width of the dorsum nasi tissue should not to be removed. Incision of the nasal septum is usually performed 10 mm from the anterior tip of the septal cartilage, which approximately corresponds to the mucocutaneous junction. Incision of the cartilage is started approximately 3-mm posterior from the mucosal incision [3].
3.
Endonasal dacryocystorhinostomy (DCR) occasionally requires a septoplasty, particularly if a Jones bypass tube is planned for insertion, because its aftercare requires easy endonasal access [2].
Lateral Nasal Wall
Lacrimal Passage
The anterior lacrimal crest, ridge, or maxillary line is formed by the underlying frontal process of the maxilla and corresponds to the anterior surface of the nasolacrimal duct [2].
The maxillary line is a curvilinear mucosal eminence projecting from the anterior middle turbinate attachment superiorly and extending inferiorly along the lateral nasal wall to the dorsum of the inferior turbinate (Fig. 5.6a, b) [11]. It corresponds intranasally to the junction of the maxilla and uncinate process and extranasally to the suture between the maxilla and lacrimal bone within the lacrimal fossa [11, 12]. A line drawn through the midpoint of the maxillary line is just inferior to the lacrimal sac–duct junction [11]. The thickness and proportion of the maxillary bone in the lacrimal sac fossa increases as the level increases from lower to upper [13]. When the height and length of the nasal bone are small, the frontal process of the maxilla is thick in the lacrimal fossa [13]. In this respect, Asians tend to have a thicker maxillary frontal process than that of Caucasians [13].
Fig. 5.6
(a) Maxillary line, agger nasi, and middle turbinate. (34-year-old female). (b). Appearance of the lateral nasal wall. The inferior turbinate and half of the middle and superior turbinates are removed. The bony opening of the nasolacrimal canal is seen. (cadaver, 89-year-old male). (c) The nasolacrimal canal courses almost parallel to the sagittal plane. (cadaver, 70-year-old male). (d) Certain length of mucosal duct, termed the valve of Hasner, extends from the bony opening of the nasolacrimal canal. (cadaver, 97-year-old female)
The lacrimal bone, which has a mean thickness of 0.057 [14] to 0.106 mm [15], is located posterior to the maxillary line. The lacrimal bone is also situated just anterior to the middle third of the uncinate process, which has an average length and width of 7.2 and 2.5 mm, respectively [14].
The nasolacrimal canal, which has an average length of 12 mm and drains into the inferior meatus (Figs. 5.1d and 5.6b) [9], originates at the base of the lacrimal fossa and is formed by the maxillary bone laterally and inferior turbinate bones medially [9]. The average width of the superior opening of the canal is 4.5–5.7 mm transversely [16–18] and 6.5–6.9 mm anteroposteriorly [17, 18]. The canal courses posteroinferiorly at an average of 12–27° (Fig. 5.1d) [17, 19–21] and almost parallel to the sagittal plane (Fig. 5.6c) [22]. However, in approximately half of individuals, the canal is directed inward against the sagittal line irrespective of the outward course of the lacrimal fossa [22, 23].
The nasolacrimal duct opening is present on the lateral nasal wall in the inferior meatus (Fig. 5.6b) [2]. The bony opening is most commonly located high up in the inferior meatus [2]. A duct orifice is present at this site in only about 10 % of individuals [24]. In most cases, a certain length of the mucosal duct extends anteroinferiorly from there [24] and reaches approximately 1 cm posterior to the anterior tip of the inferior turbinate (Fig. 5.6d) [2]. This mucosal duct is often called the valve of Hasner [2]. The shape of the opening varies considerably from round to slit like or may simply be a pit or fold [2, 24].
The relationship between the lacrimal sac and lateral nasal wall is variable; the sac may be relatively high, normal, or low compared with the adjacent anterior nasal space (Fig. 5.7a, b) [2]. This may simply reflect differently sized nasal spaces and mid-face bony development [2]. Anterior ethmoid air cells are usually found between the lacrimal fossa and lateral nasal wall in most subjects [2]. These air cells are more common in the posterior superior lacrimal fossa [2].
Fig. 5.7
(a, b) Relationship between the lacrimal sac and the middle turbinate is variable. These figures show high sac positions. (61-year-old female)
The anterior end of the middle turbinate has been thought to be a constant anatomical landmark of the lacrimal sac [2, 25, 26]. However, whether this structure can serve as a useful landmark of the lacrimal sac fossa in the vertical or anteroposterior position is unclear [27]. Up to 20 % of the lacrimal sac was reported to be situated above the axilla of the middle turbinate [28, 29]. However, another study suggested that a large part of the lacrimal sac fossa was above the axilla of the middle turbinate [30–32]. In an Asian study, the axilla of the middle turbinate was attached to the lacrimal sac fossa in more than 90 % of cases and located above the lacrimal sac fossa in 4 % [13]. A wide positional variation was shown in relation to the lacrimal sac fossa.
The horizontal position of the axilla of the middle turbinate in Asians differs from that of Caucasians. A Caucasian study [33] demonstrated that in 53.2 % of cases, the axilla of the middle turbinate was located within the lacrimal sac fossa in contrast to the conventional notion that the axilla of the middle turbinate is posterior to the lacrimal sac fossa. In an Asian study [13], the axilla of the middle turbinate was located posterior to the posterior lacrimal crest in only 2 % of cases.
More than 90 % of Caucasian specimens demonstrate the uncinate process extending beyond the posterior lacrimal crest [34]. However, in Asians, 100 % of the uncinate process reportedly attaches to the lacrimal fossa [13]. The ethmoid air cells are positioned more anteriorly in Asians than in Caucasians [13]. The anterior insertion of the uncinate process is oblique; the uncinate process generally attaches to the lacrimal bone at the lower level, becomes anterior to the maxillary bone–lacrimal bone at the middle level, and then joins the middle turbinate at the upper level [13]. The uncinate process is also helpful when approaching the lower portion of the lacrimal sac fossa [13].
Clinical Correlations
(a)
The lacrimal bone is very thin [14, 15] and easily penetrated for entrance into the nasal cavity during endonasal DCR [2]. In patients with a maxillary bone dominant fossa, the thicker bone makes it more difficult to create the osteotomy [2]. Special surgical techniques and instruments, such as a surgical drills or ultrasound aspirators, must be equipped for patients with a thick maxillary frontal process to expose the upper portion of the lacrimal sac fossa [13, 26]. In this respect, DCR for Caucasian patients with a thinner maxillary frontal process [13] may not require the use of such instruments.
(b)
Osteotomy can be easily started at the lower portion of the lacrimal sac fossa, in which the lacrimal bone constitutes the lacrimal fossa in the highest proportion and the frontal process of the maxilla is thinnest (Fig. 5.8) [13].
Fig. 5.8
Osteotomy during an endonasal dacryocystorhinostomy can be easily started at the lower portion of the lacrimal sac fossa, in which the lacrimal bone constitutes the lacrimal sac fossa in the highest proportion and the frontal process of the maxilla is thinnest. For ease of understanding, the rongeur is inserted into the nasolacrimal canal. (cadaver, 89-year-old male)
(c)
The uncinate process, which mostly extends beyond the posterior lacrimal crest, is an important factor to consider when creating an osteotomy during DCR [25, 34]. However, the sac and duct usually lie immediately anteriorly and laterally to the uncinate process, which does not need to be disturbed during surgery [2]. This notion is mostly applied to Caucasians, but not to Asians. Because the anterior ethmoid air cells always extend to the posterior lacrimal crest in Asians [2], an uncinectomy is recommended to clearly expose the lacrimal sac fossa to create a sufficient ostium.
(d)
The nasolacrimal canal opening (bony opening) is located in the ceiling of the inferior meatus [2]. However, the nasolacrimal mucosal orifice empties fairly anteriorly [24]. Therefore, a specific technique is needed to clearly observe this mucosal orifice, such as preexamination fluorescein staining or putting the inferior turbinate aside.
(e)
Because of variability in the relationship between the lacrimal sac and lateral nasal wall [2], and because of the thick maxillary frontal process in patients with a low nasal bridge [13], the precise position of the lacrimal sac is best to be confirmed by a transcanalicular illumination device during endonasal DCR [13]. The structures intervening between the lacrimal sac fossa and nasal cavity must be defined by moving the light device up and down and back and forth [13]. Diffuse light is expected in cases with an anteriorly displaced uncinate process or large agger nasi cell [13].
(f)
Most Asians may sometimes need a partial middle turbinectomy for creation of a sufficient ostium because most of the posterior lacrimal crest is covered by the axilla of the middle turbinate [13].
(g)
As described in the “Ethmoid Infundibulum” section, bone exposure after mucosal resection induces granulation [3]. Although anterior and posterior mucosal flaps are created during external DCR, bone in the upper and lower portions of the osteotomy is still exposed. These parts are at risk of granulation formation. Although the use of mitomycin C [35] or a stent [36] may prevent granulation to some extent, covering the whole osteotomy margin with the mucosal flap without bone exposure leads to a decreased risk of granulation.
Inferior Turbinate and Meatus
The inferior turbinate is the largest turbinate and occupies the lower third of the lateral nasal wall (Fig. 5.4) [2]. It arises from the medial wall of the maxillary sinus; the other turbinates arise from the ethmoid bone [9]. Its anterior tip is located 1.5–2.0 cm inside the nasal space in adults [2]. Its medial surface is usually concave, and its lateral surface is usually convex [2]. The inferior turbinate is covered by thick vascular mucosa, which often results in hypertrophy [2]. The nasolacrimal canal opening is located on the lateral nasal wall in the inferior meatus (Fig. 5.6b) [2].
The size of the meatus under each turbinate may be large or small, corresponding to the size of the bone making up the turbinate and varying with the state of mucosal and vascular engorgement of the overlying epithelium [1]. These anatomic and mucosal factors can dramatically influence the structures draining into each meatus [1].
Middle Turbinate and Meatus
The middle turbinate is part of the ethmoid bone (Fig. 5.4) [2]. When this turbinate is enlarged by air cells, it is called the “concha bullosa” (Fig. 5.9) [2] or sometimes the “interlamellar cell” [3]. The concha bullosa is classified into three types: pneumatization of the vertical lamella (lamellar type), pneumatization of the inferior bulbous portion (bulbous type), and pneumatization of the entire turbinate (extensive type) [37, 38]. These air cells usually originate from the agger nasi [2]. Normally, its lateral wall is convex and its medial wall is concave. It protects the middle meatus and its important physiological structures [2].
Fig. 5.9
Concha bullosa. (43-year-old male)
The middle meatus contains the uncinate process, hiatus semilunaris with the infundibulum, and ethmoid bulla [2] and receives drainage from the frontal, anterior ethmoid, and maxillary sinuses (Fig. 5.10) [9]. This area is important pathophysiologically because it forms part of the ostiomeatal complex [2]. The detailed anatomy of this structure is described later [2].
Fig. 5.10
Appearance of the middle meatus. This contains the uncinate process, hiatus semilunaris with the infundibulum, and ethmoid bulla and receives drainage from the frontal, anterior ethmoid, and maxillary sinuses. The posterior portion of the uncinate process divides the fontanelle into anterior and posterior parts. (cadaver, 89-year-old male)
The middle meatus divides the paranasal sinuses into anterior and posterior portions [3]. The anterior paranasal sinuses are the general term for the paranasal sinuses emptying into the middle meatus and comprise the frontal, anterior ethmoid, and maxillary sinuses [3]. The posterior paranasal sinuses are located posterior to the middle turbinate, the opening of which is around the ceiling of the posterior nasal cavity [3]. The posterior paranasal sinuses are constituted by the posterior ethmoid cells emptying into the superior meatus and the sphenoid sinus with its orifice opening to the sphenoethmoidal recess (Fig. 5.11) [3]. Conditions such as sinusitis are usually sectioned such as anterior or posterior types [3].
Fig. 5.11
Sphenoid sinus orifices. (38-year-old female)
Superior and Supreme Turbinates and Meatuses
These structures and spaces are usually small and insignificant in size compared with the other two turbinates (Fig. 5.4) [1]. These turbinates originate from the ethmoid bone. The superior turbinate has the common attachment of the middle turbinate to the skull base [39]. The supreme turbinate may be found in up to 65 % of specimens [9]. The air cells forming the posterior ethmoid sinus drain into the superior meatus with two or three ducts and occasionally into the supreme meatus [1, 40]. The olfactory neuroepithelium, which is centered principally on the area of the cribriform plate, extends to the superior turbinate and superior part of the middle turbinate to varying degrees [41].
Anatomy of Ethmoid Sinus
Overview of the Ethmoid Sinus
The ethmoid air cells are cavities comprising various sizes of honeycomb-like air cells (Fig. 5.1a) [3, 42]. The superior border is the comparatively flat roof of the ethmoid, the lateral border is the lamina papyracea, and the medial border is the lateral wall of the middle and superior meatuses and middle turbinate [3, 42]. The space is narrower anteriorly and becomes larger posteriorly, finally reaching the anterior wall of the sphenoid sinus (Fig. 5.11) [3, 42].
The cribriform plate is not a part of the ethmoid sinus, but is located medial to the attachment of the middle turbinate, separating the nose from the anterior cranial fossa (Fig. 5.12a) [1]. The two cribriform plates are separated from each other by the crista galli, and both plates lie posterior to the posterior table of the frontal sinus [1]. Each cribriform plate measures approximately 2 cm from anterior to posterior and 0.5 cm from medial to lateral [1]. The olfactory nerve endings traverse small openings in each cribriform plate to reach the olfactory bulb [1]. The narrow nasal cavity inferior to the cribriform plate is the olfactory cleavage [42]. The cribriform plates are often located lower than the roof of the ethmoid sinus, called the fovea ethmoidalis (Fig. 5.12b) [42].
Fig. 5.12
(a) Appearance of the skull base with special features of the cribriform plate, crista galli, and optic nerve. (cadaver, 81-year-old male). (b) Cribriform plate separates the nose from the anterior cranial fossa. The cribriform plates are often located lower than the fovea ethmoidalis. (42-year-old male)
Although the inside of the ethmoid sinus is complexly divided into many cells, there are several partitions dividing the sinus from anterior to posterior [3]. These are called the “basal lamellae” or “ground lamellae” [3]. When this is used in a singular form, it represents the “third basal lamella” [3]. Because the term “ground lamella” is not cited in Nomina Anatomica, the term “basal lamellae” is mainly used at present [3].
The basal lamellae of the ethmoid sinus are walls connecting the lateral nasal wall and the lamina papyracea [3]. However, only the third basal lamella clearly reaches the lamina papyracea from the lateral nasal wall [3]. Whether most of the other basal lamellae reach the lamina papyracea cannot be confirmed because of their complex structure [3]. Therefore, they are termed the “incomplete basal lamellae” [3].
The ethmoid sinus generally shows five basal lamellae that are numbered from anterior to posterior (Fig. 5.13) [3]. The first basal lamella continues to the uncinate process. The second generally originates from the anterior wall of the ethmoid bulla, occasionally including the whole ethmoid bulla with its posterior wall [43]. The third is the largest and most obvious lamella and hangs the middle turbinate [3]. This third basal lamella clearly divides the ethmoid sinus into anterior and posterior portions [3]. The fourth supports the superior turbinate, and the fifth originates at the supreme turbinate [3]. The central portion of the middle turbinate is all hung by the third basal lamella, but the anterior and posterior edges attach to the lateral nasal wall [3].
Fig. 5.13
Five basal lamellae of the ethmoid sinus. BL basal lamella. (cadaver, 89-year-old male)
The three-dimensional positional relationship between the middle meatus and third basal lamella is similar to the relationship between the body of a pigeon and its half-opened wing when its body is regarded as the lamina papyracea [3]. That is to say, the portion of the body close to the half-opened wing is the third basal lamella, and the wing inferiorly hanging from that site is the suspended middle turbinate [3].
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