Nasal Cavity
The nasal cavity is bounded by the bony pyriform aperture and the external framework of the nose
(Fig. 10.2A). The nasal cavity opens anteriorly through the skin-lined nasal vestibule into the nares and communicates posteriorly through the choanae with the nasopharynx (
Fig. 10.2B). The nasal cavity is divided in the midline by the
nasal septum, which includes both cartilaginous and bony components
(Fig. 10.2C). The cartilage of the septum is somewhat quadrilateral in form and is thicker at its margins than at its center. Its anterior margin is connected with the nasal bones and is continuous with the anterior margins of the lateral cartilages; below, it is connected to the medial crura of the greater alar cartilages by fibrous tissue (
Fig. 10.2A). Its posterior margin is connected with the
perpendicular plate of the ethmoid, its inferior margin with the vomer and the palatine process of the maxilla.
On the
lateral nasal wall are the superior, middle, and inferior nasal turbinates, and below and lateral to each turbinate (concha) is the corresponding nasal passage or meatus
(Fig. 10.3A and B). Above the superior turbinate is a narrow recess, the sphenoethmoidal recess, into which the sphenoid sinus opens. The superior meatus is a short oblique passage extending about halfway along the upper border of the middle turbinate; the posterior ethmoid cells open into the front part of this meatus. The middle meatus is below and lateral to the middle turbinate. The anatomy of the middle meatus is fully displayed by removing the middle turbinate (
Fig. 10.3A and B). The bulla ethmoidalis is the most prominent anterior ethmoid air cell. The hiatus semilunaris is a curved cleft lying below and in front of the bulla ethmoidalis. It is bounded inferiorly by the sharp concave margin of the uncinate process of the ethmoid bone and leads
into a curved channel, the infundibulum, bounded above by the bulla ethmoidalis and below by the lateral surface of the uncinate process of the ethmoid. The anterior ethmoid air cells open into the front part of the infundibulum. The frontal sinus drains through the nasofrontal duct, which in ˜50% of subjects will also drain into the infundibulum; but when the anterior end of the uncinate process fuses with the front part of the bulla, this continuity is interrupted and the frontonasal duct then opens directly into the anterior end of the middle meatus. Below the bulla ethmoidalis, and partly hidden by the inferior end of the uncinate process, is the ostium of the maxillary sinus. An accessory ostium from the maxillary sinus is frequently present below the posterior end of the middle nasal concha. The inferior meatus is below and lateral to the inferior nasal turbinate. The nasolacrimal duct opens into the inferior meatus under cover of the anterior part of the inferior turbinate.
The
roof of the nasal cavity is narrow from side to side and slopes downward (at about a 30-degree angle) from front to back. The cribriform plate, which transmits the filaments of the olfactory nerve, forms the roof of the nasal cavity medial to the superior attachment of the middle turbinate. Lateral to the middle turbinate, the fovea ethmoidalis forms the roof of the ethmoid sinuses. Careful assessment of the anatomy of the
nasal roof, especially the relationship of the cribriform plate to the fovea ethmoidalis, is critical in avoiding a cerebrospinal fluid (CSF) leak during surgery in this region. The cribriform plate is usually at a slightly lower horizontal plane than the fovea ethmoidalis forming a shallow olfactory groove. This configuration is known as Keros type I
(Fig. 10.4). However, the cribriform plate may be moderately or significantly lower than the fovea ethmoidalis resulting in a medium (Keros type II) or deep (Keros type III) olfactory groove. The topography of the roof may also be asymmetrical (
Fig. 10.4).
The
floor of the nasal cavity is concave from side to side and almost horizontal anteroposteriorly. The palatine process of the maxilla forms the anterior three-fourths, and the horizontal process of the palatine bone forms the posterior fourth of the nasal floor (
Fig. 10.2C).
The majority of the nasal cavity is lined by pseudostratified ciliated columnar epithelium, which contains mucous and serous glands (respiratory epithelium). Specialized olfactory epithelium lines the most superior portion of the nasal cavity and has direct connections with the olfactory tracts through openings in the cribriform plate.
The arteries of the nasal cavities are the anterior and posterior ethmoidal branches of the ophthalmic artery, which supply the ethmoid and frontal sinuses and roof of the nose. The sphenopalatine artery supplies the mucous membrane covering the lateral nasal wall. The septal branch of the superior labial artery supplies the anterior inferior septum. The veins form a close cavernous plexus beneath the mucous membrane. This plexus is especially well marked over the lower part of the septum and over the middle and inferior turbinates. Venous drainage follows a pattern similar to arterial supply. The lymphatic drainage from the anterior part of the nasal cavity, similar to that of the external nose, is to the submandibular group of lymph nodes (level I). Lymphatics from the posterior two-thirds of the nasal cavities and from the paranasal sinuses drain to the upper jugular (level II) and retropharyngeal lymph nodes.
The sensory nerves of the nasal cavity transmit either somatoautonomic or olfactory sensation. Somatoautonomic nerves include the nasociliary branch of the ophthalmic, which supplies the anterior septum and lateral wall. The anterior alveolar nerve, branch of the maxillary (V2), supplies the inferior meatus and inferior turbinate. The nasopalatine nerve supplies the middle of the septum. The anterior palatine nerve supplies the lower nasal branches to the middle and inferior turbinates. The nerve of the pterygoid canal (vidian) and the nasal branches from the sphenopalatine ganglion supply the upper and posterior septum and superior turbinate. The olfactory nerve fibers arise from the bipolar olfactory cells and unite in fasciculi, which form a plexus beneath the mucous membrane and then ascend passing into the skull through the foramina in the cribriform plate. Intracranially, olfactory nerve fibers enter the under surface of the olfactory bulb, in which they ramify and form synapses with the dendrites of the mitral cells of the olfactory tract.
Pterygopalatine Fossa
The pterygopalatine fossa (PPF) is a small, triangular space situated behind the maxillary sinus, in front of the pterygoid plates, and beneath the apex of the orbit. This fossa communicates with the orbit by the inferior orbital fissure, with the nasal cavity by the sphenopalatine foramen, and with the infratemporal fossa by the pterygomaxillary fissure (
Fig. 10.5). Five foramina open into it. Of these, three are on the posterior wall, which are the
foramen rotundum, the
pterygoid canal, and the
pharyngeal canal, in this order downward and medial. On the medial wall is the
sphenopalatine foramen, and below is the superior orifice of the
pterygopalatine canal (
Fig. 10.5). The fossa contains the maxillary nerve, the sphenopalatine ganglion, and the terminal part of the internal maxillary artery.
The fissures and foramina of the PPF serve as “highways” for spread of cancer from the sinonasal region to the orbit, infratemporal fossa, and cranial base.
Anterior Cranial Fossa
The floor of the anterior fossa is formed by the orbital plates of the frontal bone, the cribriform plate of the ethmoid, and the lesser wings and front part of the body of the sphenoid. In the midline, it presents, from anterior to posterior, the
frontal crest for the attachment of the falx cerebri; the
foramen cecum, which usually transmits a small vein from the nasal cavity to the superior sagittal sinus (SSS); and the
crista galli, the free margin of which affords attachment to the falx cerebri
(Fig. 10.9). On either side of the crista galli is the
olfactory groove formed by the cribriform plate, which supports the olfactory bulb and presents foramina for the transmission of the olfactory nerves. Lateral to either olfactory groove are the internal openings of the anterior and posterior ethmoidal foramina; the anterior, situated about the middle of the lateral margin of the olfactory groove transmits the anterior ethmoidal vessels and the nasociliary nerve; the nerve runs in a groove along the lateral edge of the cribriform plate; and the posterior ethmoidal foramen opens at the back part of this margin under cover of the projecting lamina of the sphenoid and transmits the posterior ethmoidal vessels and nerve. More laterally, the cranial floor forms the orbital roof and supports the frontal lobes of the cerebrum. Farther back in the middle is the planum sphenoidale, forming the roof of the sphenoid sinus, and the anterior margin of the chiasmatic groove, running laterally on either side to the upper margin of the optic foramen (
Fig. 10.9).
Orbit
The orbits are two quadrilateral pyramidal cavities, their bases being directed forward and lateral, and their apices backward and medial, so that their long axes diverge at a 45-degree angle and if continued backward would meet over the body of the sphenoid. The orbit is anatomically defined by seven bones
(Fig. 10.10): frontal, zygomatic, maxillary, lacrimal, ethmoid, sphenoid, and palatine, and by the orbital
septum, which originates at the arcus marginalis, fusing with the levator aponeurosis above and the capsulopalpebral fascia below. It is bounded by the ethmoid and sphenoid sinuses at its medial aspect, the frontal sinus superomedially, the cranial vault superiorly and posteriorly, the temporal fossa laterally, and the maxillary sinus inferiorly. Each orbital cavity has a
roof, a
floor, a
medial and a
lateral wall, a
base, and an
apex.
The roof is formed anteriorly by the orbital plate of the frontal bone and posteriorly by the lesser wing of the sphenoid. It presents medially the trochlear fovea for the attachment of the cartilaginous pulley of the superior oblique muscle and laterally the lacrimal fossa for the lacrimal gland.
The floor is formed mainly by the orbital surface of the maxilla, anteriorly and laterally by the orbital process of the zygomatic bone, and posterior and medially, to a small extent, by the orbital process of the palatine bone. At its medial angle is the superior opening of the nasolacrimal canal, immediately to the lateral side of which is a depression for the origin of the inferior oblique muscle. Running anteriorly near the middle of the floor is the infraorbital canal, ending anterior to the maxilla in the infraorbital foramen and transmitting the infraorbital nerve and vessels.
The medial wall is formed anteriorly to posteriorly by the frontal process of the maxilla, the lacrimal bone, the lamina papyracea of the ethmoid, and a small part of the body of the sphenoid anterior to the optic foramen. Anteroinferiorly, the lacrimal sac is situated between the anterior and posterior lacrimal crests at the junction between the medial wall and the floor. The lacrimal part of the orbicularis oculi arises from the posterior lacrimal crest. At the junction of the medial wall and the roof, the frontoethmoidal suture presents the anterior and posterior ethmoidal foramina, the former transmitting the nasociliary nerve and anterior ethmoidal vessels and the latter the posterior ethmoidal nerve and vessels. These foramina indicate the level of the cranial base within the orbit.
The lateral wall is formed by the orbital process of the zygomatic and the orbital surface of the greater wing of the sphenoid. On the orbital process of the zygomatic bone are the orbital tubercle (Whitnall) and the orifices of one or two canals, which transmit the branches of the zygomatic nerve. Between the roof and the lateral wall, near the apex of the orbit, is the superior orbital fissure (SOF). Through this fissure, the oculomotor, the trochlear, the ophthalmic division of the trigeminal (V1), and the abducens nerves enter the orbital cavity, also some filaments from the cavernous plexus of the sympathetic and the orbital branches of the middle meningeal artery. Passing posteriorly through the fissure are the ophthalmic vein and the recurrent branch from the lacrimal artery to the dura mater. The lateral wall and the floor are separated posteriorly by the inferior orbital fissure, which transmits the maxillary nerve (V2) and its zygomatic branch, the infraorbital vessels, and the ascending branches from the sphenopalatine ganglion.
The base of the orbit (orbital rim), quadrilateral in shape, is formed superiorly by the supraorbital arch of the frontal bone, in which is the supraorbital notch or foramen for the passage of the supraorbital vessels and nerve; inferiorly by the zygomatic bone and maxilla, united by the zygomaticomaxillary suture; laterally by the zygomatic bone and the zygomatic process of the frontal joined by the zygomaticofrontal suture; and medially by the frontal bone and the frontal process of the maxilla united by the frontomaxillary suture.
The apex is situated in the posterior aspect of the orbit. The optic foramen is a short, cylindrical canal, through which passes the optic nerve and ophthalmic artery.
The extraocular muscles—four rectus muscles and two obliques—effect movement of the eye. The third cranial nerve innervates all but the lateral rectus and the superior oblique muscles, which are innervated by the fourth and sixth cranial nerves, respectively. The rectus muscles originate at the annulus of Zinn and insert on the globe forming a muscle cone, which is the central anatomic space in the orbit.
The
lacrimal system is composed of secretory and drainage systems. Secretory glands—the glands of Moll, Krause, and Wolfring—may be found along the margin of the eyelid. The lacrimal gland with its palpebral and orbital lobes is located in the superotemporal orbit
(Fig. 10.11). The lacrimal drainage system, located in the inferonasal orbit, is represented by
the puncta, canaliculi, lacrimal sac, and nasolacrimal duct. Tumor involvement of the lacrimal system may present with epiphora.
The skin of the eyelid is continuous with the palpebral and bulbar conjunctivae, which are, in turn, contiguous with the globe. Each of these epithelial surfaces represents a potential site of origin for cancer.