Chapter 23. Nasal Cavity

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Big Picture

The nasal cavity is divided into two lateral compartments separated down the middle by the nasal septum. The nasal cavity communicates anteriorly through the nostrils and posteriorly with the nasopharynx through openings called choanae. The nasal cavities and septum are lined with a mucous membrane and are richly vascularized by branches of the maxillary, facial, and ophthalmic arteries. The nasal cavity receives innervation via branches of the olfactory [cranial nerve (CN) I], ophthalmic (CN V-1), and maxillary nerves (CN V-2).

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Boundaries of the Nasal Cavity

The nasal cavity is bordered by the following structures (Figure 23-1A–C):

• Roof. Formed by the nasal, frontal, sphenoid, and ethmoid bones (cribriform foramina, which transmits CN I for smell).
• Floor. Formed by the maxilla and the palatine bones. The incisive foramen transmits branches of the sphenopalatine artery and the nasopalatine nerve for general sensation from the nasal cavity and palate.
• Medial wall (nasal septum). Formed by the perpendicular plate of the ethmoid bone, the vomer bone, and the septal cartilage.
• Lateral wall. Formed by the superior, middle and inferior nasal conchae. In addition, the maxillary, sphenoid, and palatine bones contribute to the lateral wall. The lateral wall contains the following openings:
  • Sphenoethmoidal recess. The space between the superior nasal concha and the sphenoid bone, with openings from the sphenoid sinus.
  • Superior meatus. The space inferior to the superior nasal concha, with openings from the posterior ethmoidal air cells.
  • Middle meatus. The space inferior to the middle nasal concha, with openings for the frontal sinus via the nasofrontal duct, the middle ethmoidal air cells on the ethmoidal bulla, and the anterior ethmoidal air cells and maxillary sinus in the hiatus semilunaris.
  • Inferior meatus. The space inferior to the inferior nasal concha, with an opening for the nasolacrimal duct, which drains tears from the eye into the nasal cavity.
  • Sphenopalatine foramen. An opening posterior to the middle nasal concha receives the nasopalatine nerve and the sphenopalatine artery from the pterygopalatine fossa into the nasal cavity.

Rhinorrhea, or “runny nose,” is evident by the clear fluid that leaks out of the nostrils. A runny nose usually accompanies the common cold. Rhinorrhea usually results from overproduction of mucus resulting from conditions such as sinusitis, hay fever, and allergic reactions. However, rhinorrhea that occurs after an accident involving head trauma may indicate a basilar skull fracture, resulting in leakage of cerebrospinal fluid from the subarachnoid space through the fracture (often the ethmoid bone) into the nasal cavity and out of the nostrils.

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Nerve Supply of the Nasal Cavity

The nasal cavity contains the following nerves (Figure 23-1D):

• CN I. Originates in the mucosa lining the superior nasal concha and the superior septum, where the nerve provides special sensation for smell. Neurons from CN I course from the nasal cavity into the anterior cranial fossa and through the numerous foramina of the cribriform plate of the ethmoid bone. The neurons enter the olfactory bulb, where they synapse with interneurons that course along the olfactory tract, transporting information to the brain.

Anosmia (lack of smell) can result from trauma to the ethmoid bone and the nasal region, where the optic nerve (CN II) endings become damaged.

• CN V-1. Provides general sensation to the superior aspect of the nasal cavity via the anterior ethmoidal nerve, a branch of the nasociliary nerve.
• CN V-2. Provides general sensation to most of the nasal cavity via branches of the nasopalatine and lateral nasal nerves.
  • CN VII (facial nerve). Provides visceral motor innervation to the nasal glands. CN VII exits the cranial cavity through the internal acoustic meatus. Within the temporal bone, CN VII gives rise to the greater petrosal nerve, which carries the visceral motor preganglionic parasympathetic neurons from CN VII en route to the nasal cavity. The greater petrosal nerve joins up with the deep petrosal nerve to form the nerve of the pterygoid canal (Vidian nerve). The nerve of the pterygoid canal enters the pterygopalatine fossa, where parasympathetics from CN VII synapse. Postganglionic parasympathetic neurons exit the ganglion and “hitch-hike” along CN V-2 branches to the nasal mucosa, where the mucosal glands are innervated.

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Vascular Supply of the Nasal Cavity

The nasal cavity receives its vascular supply via the following arteries (the nasal veins parallel the arteries) (Figure 23-1E):

• Sphenopalatine artery. Principal blood supply to the septum and the lateral nasal wall.
• Anterior and posterior ethmoidal arteries. Supply the superior portion of the nasal cavity.
• Greater palatine artery. Supplies the inferior nasal septum via the incisive canal.
• Facial artery. Supplies the anterior portion of the nasal septum and the lateral nasal wall.

Kiesselbach's area (plexus) is a region in the anteroinferior region of the nasal septum where branches of the sphenopalatine, anterior ethmoidal, greater palatine, and facial arteries anastamose. Most nosebleeds (epistaxis) usually occur in this area.

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Big Picture

The paranasal sinuses are hollow cavities within the ethmoid, frontal, maxillary, and sphenoid bones (Figure 23-2A and B). They help to decrease the weight of the skull, resonate sound produced through speech, and produce mucus. The paranasal cavities communicate with the nasal cavity, where mucus is drained. Branches of CN V provide general sensory innervation.

The paranasal sinuses are easily recognizable on an x-ray because the sinuses are filled with air and thus appear as darker shadows on the radiograph.

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Ethmoidal Sinus

Unlike the frontal, maxillary, and sphenoid paranasal sinuses, the ethmoidal sinus consists of numerous small cavities (air cells) within the bone, as opposed to one or two large sinuses. The subdivisions of the ethmoidal air cells (anterior, middle, and posterior) communicate with the nasal cavity.

• Anterior ethmoidal air cells. Drain through tiny openings in the hiatus semilunaris of the middle meatus.
• Middle ethmoidal air cells. Drain through the ethmoidal bulla of the middle meatus.
• Posterior ethmoidal air cells. Drain through openings in the superior meatus.

The posterior ethmoidal nerve (CN V-1) provides general sensory innervation for the ethmoidal air cells.

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Frontal Sinus

The frontal sinus is located in the frontal bone and opens into the anterior part of the middle meatus via the frontonasal duct. The supraorbital nerve (CN V-1) provides general sensory innervation for the frontal sinus.

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Maxillary Sinus

The maxillary sinus is the largest of the paranasal sinuses and is located in the maxilla, lateral to the nasal cavity and inferior to the orbit. The maxillary sinus opens into the posterior aspect of the hiatus semilunaris in the middle meatus. The infraorbital nerve (CN V-2) primarily innervates the maxillary sinus.

Maxillary sinusitis results from inflammation of the mucous membrane lining the maxillary sinus and is a common infection because of its pattern of drainage. The maxillary sinus drains into the nasal cavity through the hiatus semilunaris, which is located superiorly in the sinus (Figure 23-2C). As a result, infection has to move against gravity to drain. Infection from the frontal sinus and the ethmoidal air cells potentially can pass into the maxillary sinus, compounding the problem. In addition, the maxillary molars are separated from the maxillary sinus only by a thin layer of bone. Therefore, if an infecting organism erodes the bone, infection from an infected tooth can potentially spread into the sinus. The infraorbital nerve (CN V-2) innervates the maxillary teeth and sinus; therefore, pain originating from a tooth or the sinus may be difficult to differentiate.

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Sphenoid Sinus

The sphenoid sinus is contained within the body of the sphenoid bone and is inferior to the sella turcica. The sphenoid sinus opens into the sphenoethmoidal recess of the nasal cavity. The posterior ethmoidal nerve (CN V-1) and branches from CN V-2 provide general sensory innervation of the sphenoid sinus.

The pituitary gland is located in the roof of the sphenoid bone. The gland is important for the production and release of hormones targeting the gonads, adrenals, thyroid, kidney, uterus, and the mammary glands. Tumors of the pituitary gland can cause an overproduction of these hormones or may affect vision by compressing CN II. Surgery may be necessary to remove the tumor. The sphenoid sinus is separated from the nasal cavity by a thin layer of bone. Therefore, the pituitary gland can be approached surgically by going through the nasal cavity into the sphenoid sinus and finally through the superior aspect of the sphenoid sinus into the sella turcica, where the pituitary gland is located (transsphenoidal hypophysectomy).