Anatomy, Head and Neck, Nasopalatine Nerve

Structure and Function

The nasopalatine nerve is a branch of the maxillary division of the trigeminal nerve (5th cranial nerve or CN V). The trigeminal nerve is a mixed sensorimotor nerve that exits the brain from the lateral surface of the pontine body as 2 roots, one large with sensory functions and the other small with motor impulses. Both roots travel from the pons to the middle cranial fossa floor to reach the trigeminal ganglion in a temporal bone depression known as the Meckel cave. Sensory root fibers synapse with the ganglion and give rise to the trigeminal nerve's 3 main sensory divisions: the ophthalmic and maxillary nerves and the sensory portion of the mandibular division. Unlike its sensory counterpart, the trigeminal nerve's motor root bypasses the trigeminal ganglion without synapsing and joins the mandibular branch's sensory root at the foramen ovale.

The maxillary division of the trigeminal nerve is sensory in function. This nerve leaves the cranium via the foramen rotundum and enters the pterygopalatine fossa. The pterygopalatine fossa is a cone-shaped space posterior to the maxilla, bounded by the maxillary, sphenoid, and palatine bones. The fossa contains many important anatomical structures, including the maxillary nerve and arteries and the pterygopalatine ganglion. The maxillary nerve divides into its branches at the pterygopalatine fossa. Some branches emerge from the maxillary nerve only after synapsing with the pterygopalatine ganglion. Other branches diverge directly from the main root of the maxillary nerve. The nasopalatine nerve emerges from the pterygopalatine ganglion (see Image. Trigeminal Nerve, Nasopalatine Distribution).

The nasopalatine nerve is the largest of the pterygopalatine ganglion's branches. This nerve enters the nasal cavity via the sphenopalatine foramen (see Image. Sphenopalatine Foramen). This foramen forms from the articulation of the palatine and sphenoid bones in the lateral nasal wall.[2]

Once in the nasal cavity, the nasopalatine nerve passes inferior to the sphenoid sinus ostium to reach the nasal septum. The nerve then courses between the periosteum and the nasal septum's mucous membrane, providing sensation to the mucosa of this region. From here, the nasopalatine nerve travels anteriorly and inferiorly to pierce the hard palate anteriorly through the nasopalatine canal, which links the nasal and oral cavities (see Image. Nasopalatine Region Innervation). Other structures in the nasopalatine canal include the terminal branch of the nasopalatine artery, a small amount of fatty tissue, and the palatine glands.

The right and left nasopalatine nerves anastomose before emerging into the oral cavity through the incisive foramen.[3] The incisive foramen is an opening in the anterior maxilla just behind the central incisors. The nasopalatine nerve communicates with both greater palatine nerves after exiting the incisive foramen.[4] Together, these nerves provide general sensory innervation to the hard palate.

The nasopalatine nerve supplies general sensory innervation to the palate's anterior region. The nerve also provides innervation to the maxillary incisors in some individuals.[5] A nasopalatine nerve block anesthetizes the palatal tissues of the 6 maxillary anterior teeth. The greater palatine nerve provides general sensory innervation to the soft tissues of the palate from the canines onward. However, these 2 nerves have overlapping distributions.[6][7] The greater palatine nerve seems to adopt a more significant role in innervating the anterior palate than the nasopalatine nerve during childhood.[8]

Embryology

The trigeminal nerve and its branches originate from the 1st pharyngeal arch, which develops in the 3rd to 4th week of gestation.[9] The nasopalatine canal forms as part of the primary palate, created by the fusion of the 2 medial nasal prominences at the midline. The canal marks the junction between the primary and secondary palates, the latter composed of palatine shelves growing from the maxillary prominences. The nasopalatine canal initially appears as a wide space but narrows and fills with fibrous tissue as the incisive bone ossifies at 12 to 15 weeks.[10]

Blood Supply and Lymphatics

The nasopalatine artery, also known as the sphenopalatine artery, is a branch of the internal maxillary artery.[11] The nasopalatine artery enters the nasal cavity via the sphenopalatine foramen to supply the frontal, maxillary, ethmoid, and sphenoid sinuses. One nasopalatine artery branch descends into the nasopalatine canal to anastomose with the descending palatine artery, entering the incisive foramen 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 and joins 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 empties via the pharyngeal venous plexus.

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

Surgical Considerations

The nasopalatine nerve may be traumatized or dissected during surgery for removing supernumerary teeth. Younger patients have been shown to regain almost immediate sensation on the anterior palate after encountering such complications. In contrast, patients older than 14 do not show the same quick recovery. The nasopalatine nerve's contribution to the anterior palate's innervation seems to increase with age and maxillary development. Dysesthesia of the anterior palate or maxillary teeth may occur after septoplasty, mainly if the procedure addresses low septal spurs and uses cautery or osteotomes.[12]

The nasopalatine duct cyst is a developmental nonodontogenic maxillary cyst, arising from the nasopalatine duct's epithelial remnants that proliferate spontaneously or due to trauma, infection, or mucus retention. This lesion is the most common nonodontogenic maxillary cyst, occurring in 1% of the population, typically affecting middle-aged individuals. Treatment requires surgical excision via a sublabial or palatal approach. The cyst is not a true neoplasm and can thus also be treated by marsupialization to the nasal cavity.[13][14]

Clinical Significance

The nasopalatine nerve block is used to achieve soft tissue anesthesia for procedures involving the premaxilla, such as cleft palate repair. In some patients, this block can also anesthetize the pulp of the maxillary incisors. This procedure requires the deposition of the anesthetic solution in the incisive canal, resulting in bilateral anesthesia of the nasopalatine nerve and blocking pain fibers in the palatal mucosa of the anterior 6 maxillary teeth.

The technique traditionally involved a single penetration into the canal, which was too traumatic and painful for the patient. The current practice entails multiple injections, with the first one performed on the labial side in the interdental papilla, entering horizontally with a 30-gauge needle. The solution diffuses to the palate after achieving buccal anesthesia. However, this block cannot be accomplished in patients with complete cleft palates, as they have malformed premaxillae.[15][16]

Nasopalatine canal measurement is also important in the field of implant dentistry, as it helps prevent intraoperative complications, such as a nasopalatine canal or buccal bone plate perforation. To date, traditional imaging modalities have proven ineffective, given the bony complexity of this region. Thus, cone beam computed tomography has seen increased use with success.