Anatomy, Head and Neck, Nasopalatine Nerve

Also known as nervus incisivus, the nasopalatine nerve is a division of the maxillary branch of the trigeminal nerve. Its function is to provide sensation to the anterior palate. The sphenopalatine artery supplies the same area it innervates. The pathological development of a cyst in the incisive canal can cause impingement of the nasopalatine nerve and limit its function. Clinically, injecting local anesthesia or performing nasopalatine nerve block facilitates procedures of the palate/maxilla.

The nasopalatine nerve is a division of the maxillary branch of the trigeminal nerve. As the trigeminal nerve is sensory, the nasopalatine nerve is also a sensory nerve. It courses into the nasal cavity through the pterygopalatine ganglion to enter the sphenopalatine foramen. It passes inferior to the ostium of the sphenoid sinus to reach the septum, lying between the periosteum and the mucous membrane where it provides sensation to the nasal septum. From here, it courses inferiorly to pierce the hard palate anteriorly through the nasopalatine canal, which links the nasal and oral cavities. Other structures in this canal include the terminal branch of the nasopalatine artery, a small amount of fat, and palatine glands. The inferior opening of the nasopalatine canal is called the incisive foramen.[1] Here, the nasopalatine nerve communicates with the anterior palatine nerve. The extent to which it innervates the local mucosa, as well as its relationship with the anterior (greater) palatine nerve, has historically been a topic of debate.[2]

The anterior palatine nerve innervates the gingivae and the structures of the maxillary teeth as far forward as the canines, while the nasopalatine nerve primarily innervates the mucosa surrounding the incisive papilla and the gingival margins of the maxillary incisors.[3] However, there is an overlap in the watershed area between these two nerve distributions.

The territory of the nasopalatine nerve also differs depending on the age of the subject in question. From data of nasopalatine nerve resection during the removal of supernumerary teeth, younger patients have been shown not to have sensory deficits, while the adolescent and adult groups did. This finding led to the conclusion that the nasopalatine nerve assumes the function of the anterior palatine nerve around age fourteen years.[4] The clinical implication here is that different anesthetic plans may be necessary to accommodate these changes with development depending on the age of the patient.

As the nasopalatine nerve is a derivative of the maxillary nerve, the V2 branch of the trigeminal nerve (CN V); it originates from the first pharyngeal arch. The first pharyngeal arch appears at the beginning of the fourth week of gestation, and cranial nerve V2 spreads to provide sensation to the maxillary region of the face.

The nasopalatine canal forms as part of the primary palate, which itself results from the fusion of the two medial nasal prominences in the midline. It is then the point of union between the primary and secondary palate, which is composed of the palatine shelves- outgrowths of the maxillary prominences.  As development occurs, the nasopalatine nerve passes through a wide tissue space initially, but as ossification of the incisive bone takes place at 12 to 15 weeks, the incisive canal becomes narrow and fills with fibrous tissue.[5]

The nasopalatine (or sphenopalatine) artery is a branch of the internal maxillary artery that enters the nasal cavity via the sphenopalatine foramen to supply the frontal, maxillary, ethmoid, and sphenoid sinuses. One branch descends into the incisive canal to anastomose with the descending palatine artery, entering the nasopalatine canal with the nasopalatine nerve.

The veins of the palate are diffuse and variable. The primary vessel draining this region is the facial vein which courses from the medial canthus, behind the facial artery, to join with the retromandibular vein below the mandible; this union is sometimes termed the common facial vein. Venous drainage of the hard palate is via the pterygoid plexus of veins in the infratemporal fossa, while the soft palate drains via the pharyngeal venous plexus.

Lymphatics from the palate generally terminate in the jugulodigastric nodes. The drainage of the palatal gingivae varies, as sometimes it occurs directly via the jugulodigastric nodes and sometimes indirectly via the submandibular nodes. Posterior soft palate lymphatics drain into the pharyngeal lymph nodes.