1 Nasal Anatomy
Summary
The nasal cavity is the space comprised in between the external nares and the choanae. In the sagittal axis, this space is divided into two cavities by the nasal septum. In the coronal plane, the nasal cavities extend from the palate to the skull base and from the nasal septum to the lateral nasal wall.
To systematize the surgical endoscopic anatomy of the nose, we approach each nasal cavity as a hexahedron. The anterior and posterior walls of the cube are the nares and the choanae, respectively, the medial wall is the nasal septum, the lateral wall is the homonymous part of the nose, the inferior wall is the nasal floor, and the superior wall is the nasal vault.
The paranasal sinuses are adjacent to these nasal walls. In the roof of the nasal cavity, the frontal sinus, the ethmoidal cells, and the sphenoid sinus are located in an anteroposterior way. The maxillary sinuses are located beside the lateral nasal walls.
The anatomy of the nasal cavity and the paranasal sinuses is exposed/discussed in this chapter in a similar way as an endoscopic approach is performed with respect to the underlying anatomy and each nasal wall.
1.1 Front Door to Nasal Cavity
1.1.1 Piriform Aperture
The piriform aperture acts as the door to the bony structures of the nose. Its boundaries are superiorly the inferior edge of both the nasal bones, laterally the nasal (ascending) processes of the maxilla, and inferiorly the horizontal processes of the maxillary bones. The junction between the latter ones forms the anterior nasal spine, a keel-shaped protrusion in which the nasal septum is firmly attached (Fig. 1‑1).
1.1.2 Nasal Pyramid
The bony framework of the piriform aperture represents the insertion of the cartilaginous structures supporting the nasal pyramid: upper lateral cartilages (ULCs) and lower lateral cartilages (LLCs). The ULCs are triangle shaped. Its superior insertion is under the nasal bones where they are strongly attached. Medially, its edge merges with the nasal septum and the contralateral ULC at the keystone area (Fig. 1‑2). This union with the nasal septum shapes a decreasing angle in the nasal cavity from superior to inferior (from 70 to 10–15 degrees), which is of paramount importance to determine the nasal airflow. At this point, between the nasal septum, ULC, the head of the middle turbinate, and the floor of the nasal cavity, the coronal section is called “nasal valve” as it constitutes the place of maximal resistance to nasal airflow. Values of this valvular nasal angle under 10 degrees may result in nasal obstruction. 1 The vertex of the ULC is inserted laterally in the frontal process of the maxilla. The inferior edge of the ULC is placed under the superior edge of the LLC crus lateralis. The LLC is horseshoe shaped and has three portions: crus medialis, crus lateralis, and intermediate crus or dome. This cartilage is the main support to the nasal vestibule that is the natural entry to the nasal cavity. Because of its fibroelastic insertions to the bony framework of the piriform aperture and to the musculocutaneous components of the nasal pyramid, it offers a significant elasticity that facilitates the indispensable maneuvers for the endoscopic approaches to the nose.
1.2 Medial Wall of Nasal Cavity: Nasal Septum
The nasal septum is constituted by the septal cartilage and four bones: the perpendicular plate of the ethmoid, the vomer, septal crests of the palatine, and maxillary bones.
Classically the septum was divided by Cottle into five areas, corresponding to the projection of anatomical structures located in the lateral nasal wall: area I, from the external nostril to the nasal valve; area II, corresponding to the nasal valve; area III, from the nasal valve to the anterior limit of the head of the turbinates; area IV, corresponding to the projection of the turbinates; and area V, from the tail of the turbinates to the choana. This classification may be of interest to designate precisely the anatomical location of nasoseptal perforations (Fig. 1‑3).
1.2.1 Septal Cartilage
Its anterosuperior edge articulates with the suture between both the nasal bones in the most superior portion; its middle part is the place of insertion of the ULCs of the nasal dorsum and its lower third forms the “supratip” of the nose, being the main support for the nasal tip. The anteroinferior edge hangs just over the crus medialis of the LLCs and separated of them by the membranous septum. The posteroinferior edge articulates with the anterior nasal spine, the septal crests of both the maxillary bones (also named wings of the premaxilla), and the anterior half of the vomer. Interesting in this area are the fibrous junctions that keep the septal cartilage firmly attached to its inferior bony insertions: direct and crossing fibers from periosteum to perichondrium. The posterosuperior edge of the cartilage joins the perpendicular plate of the ethmoid in an oblique line from anterior to posterior and superior to inferior. This boundary shows a clear change of consistency between the bone and cartilage when surgically exposed.
1.2.2 Perpendicular Plate of Ethmoid
Its superior edge is inserted in the cribriform plate, where it continues inside the endocranium as the crista galli. The anterosuperior edge of the plate is projected forward to articulate with the nasal spine of the frontal bone and the nasal bones. As it has been mentioned, its anteroinferior edge articulates with the septal cartilage. Its inferior edge joins the vomer, often resulting in a bony lateral ridge (Fig. 1‑4). In the posterior edge it articulates with the vertical crest located in the middle of the rostrum sphenoidale, in between both ostia of the sphenoid sinuses.
1.2.3 Vomer
It has a pointing forward wedge shape. Its posteroinferior edge is the medial limit and the separation of the choanae. Its posterosuperior limit articulates through a V-shaped sulcus with the middle crest of the rostrum sphenoidale. Its anterosuperior edge is firmly attached to the perpendicular plate of the ethmoid bone and the septal cartilage. Its inferior edge articulates with the vertical septal crests of the maxillary and palatine bones (see Fig. 1‑3).
1.2.4 Septal Crests of Palatine and Maxillary Bones
The septal crests of these two bones form the inferior strip of the nasal septum. They are oriented vertically and join with its contralateral homologous, creating a sulcus where the perpendicular plate of the ethmoid and the septal cartilage are inserted. Often, a septal spur is observed, frequently bilateral, in the line of the joint between the septal cartilage and the septal crest of the maxillary bone, which hinders the subperiosteal-subperichondrial dissection of this area—and even more so because this is the place where the attaching fibers cross from one side to another (see Fig. 1‑4).
1.3 Lateral Nasal Wall
1.3.1 Lateral Wall of Nasal Cavity
We describe the different structures and reliefs that will be found in the endoscopic exploration from anterior to posterior (Fig. 1‑5).
Frontal Process of Maxillary Bone
The anterior edge of the frontal or ascending process of the maxillary bone forms the piriform aperture in its lower part and articulates with the nasal bones superiorly. Its superior limit joins the frontal bone. Its medial surface is the most anterior part of the lateral wall of the nose and presents two horizontal crests for the insertion of the inferior and the middle turbinates. The posterior edge of the frontal process articulates with the lacrimal bone and forms what is endoscopically known as maxillary crest or lacrimal bulge, a vertical relief of thick bone that is covering medially the lacrimal sac (Fig. 1‑6).
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