Lateral Nasal WallCHAPTER 1

It is far easier to understand the endoscopic anatomy that we encounter intraoperatively and its surgical implications, if we have made a prior study of the lateral nasal wall as it appears in a cadaveric sagittal section of the head.

The lateral nasal wall (Fig. 1.1) shows broadly two regions, an anterior one-third which is relatively featureless consisting of vestibule and atrium and a posterior two-thirds which shows three major elevations, i.e. the turbinates. Posterior to the turbinates is the region of sphenoid sinus and the nasopharynx. The posterior end of inferior turbinate is at the level of opening of the eustachian tube whereas the middle turbinate ends at the level of roof of posterior choana. The roof of nasal cavity, i.e. the skull base, slopes from above downwards starting anteriorly as the posterior wall of frontal sinus and ending posteriorly as the roof of sphenoid sinus. The part of skull base formed by the frontal and sphenoid bones is relatively thick while the central part which is formed by cribriform plate of ethmoid bone is thin and is perforated by a number of olfactory nerves.

The vestibule is skin lined and there is a clear line of demarcation between the skin and the mucosa of the atrium. This mucosa of the atrium is closely bound to the underlying bone, i.e. the nasal bone and frontonasal process of maxilla. A bulge is often seen in the atrium just anterior and a little superior to the anterior attachment of middle turbinate. This is due to the underlying agger nasi cell. An ill-defined ridge extends downwards from this bulge up to the inferior turbinate. This is the maxillary line and it overlies the nasolacrimal duct.

The inferior turbinate is a separate bone whereas the middle and superior turbinates are parts of the ethmoid bone. Although the inferior turbinate appears relatively straight, its attachment is in the form of an inverted “V”. The maxillary line mentioned earlier ends at the apex of this “V” and the underlying nasolacrimal duct enters the inferior meatus at this point. The nasolacrimal duct travels submucosally for a few mm before opening in the lateral wall of the inferior meatus. This opening is guarded by a fold of mucosa called the Hasner's valve.

When the middle turbinate is trimmed to expose the middle meatus, we can see two important elevations, the anterior boomerang-shaped ridge is the uncinate process which consists of a vertical and a horizontal limb with an intermediate transitional part. Posterior to this is the well pneumatized and most constant anterior ethmoidal cell, namely the ethmoidal bulla. These structures are separated by a semilunar groove called the hiatus semilunaris. The hiatus semilunaris is two-dimensional and leads into a three-dimensional space called the infundibulum. The uncinate process, the bulla and the intervening infundibulum form the key area or the ostiomeatal unit (Fig. 1.2) into which the frontal, the maxillary and anterior ethmoidal sinuses drain.

The bony opening in the medial wall of the maxillary bone which leads into the maxillary sinus is called the maxillary hiatus. It is partially closed in the living by various processes of different bones as well as by mucosa. Hence the maxillary ostium itself is just a few mm in diameter. It lies deep to the intermediate/horizontal portion of the uncinate process. Since it lies deep within the infundibulum close to the attachment of the uncinate, it can therefore be seen only when the entire width of the uncinate process is removed. It is usually ovoid in shape and has a three-dimensional tunnel like configuration. It is related to two critical areas, superiorly to the lamina papyracea and the orbit, anteriorly to the nasolacrimal duct. A branch of the sphenopalatine artery runs along the lateral wall at a variable distance from the posterior margin of the foramen.

The infundibulum leads anterosuperiorly either directly and indirectly into the frontal recess (Fig. 1.4). The frontal recess is bounded anteriorly by the agger nasi cell, which is considered to be a part of the frontal recess. Therefore, the anterior wall of the frontal recess is formed by the anterior wall of the agger nasi cell. The posterior wall is formed by the bulla ethmoidalis. If there is a suprabullar recess it will open into the posterior wall of the frontal recess. The lateral wall of the frontal recess is formed by the lamina papyracea. The medial wall is formed by the middle turbinate. Superiorly the frontal recess opens via the frontal ostium into the frontal sinus. Seen in Figure 1.4, the frontal sinus opening is funnel shaped and is placed at the posterior and medial end of the floor of the frontal sinus. This funnel-shaped region is called the frontal infundibulum. Thus in sagittal cross section the frontal infundibulum, frontal ostium and the frontal recess together form the “hour-glass configuration” so often described.

The upper end of the uncinate process lies within the frontal recess. It shows great variation in anatomy. It can:

The ethmoidal cells are classified into anterior and posterior ethmoid cells depending, not so much on their actual locations, as on their drainage pattern. The anterior ethmoid cells drain into the middle meatus anterior to ground lamella. The posterior ethmoid cells drain into the superior meatus or the sphenoethmoidal recess posterior to ground lamella. The posterior ethmoid cells are fewer and larger than the anterior ethmoid cells. The posterior most ethmoid cell always overlies the sphenoid sinus for a variable distance.

The sphenoethmoidal recess is the region in the lateral nasal wall where the posterior ethmoid cells are related to the sphenoid sinus (Fig. 1.6). This recess contains the superior turbinate and any other supernumery turbinates, e.g. the supreme turbinate. The sphenoid ostium opens high on the anterior wall of the sphenoid into the sphenoethmoidal recess. The anterior wall of the sphenoid is relatively thinner superiorly and much thicker inferiorly at the roof of the posterior choana. The sphenoid sinus is classified into various types depending on the pneumatization (see Fig. 2.11).

The study of the bones forming the nose and paranasal sinuses, the lateral nasal wall in a sagittal section, the endoscopic anatomy and the radiological anatomy as seen in CT scans form the four major pieces of the puzzle which completes the three-dimensional picture of nose, paranasal sinus and the skull base. Acquiring a detailed understanding of all these four components is the “rite of passage” to becoming a safe and effective endoscopic surgeon.