Nasopalatine Duct Cyst

Jamie Larmie, B.S.; Louis Mandel, D.D.S.

From the Division of Oral and Maxillofacial Surgery, Columbia University College of Dental Medicine, New York, NY.

ABSTRACT

The nasopalatine duct cyst (NPC) develops in the incisive canal from embryologic remnants of the nasopalatine duct. Clinically, the NPC’s presence is usually confined within the limits of the incisive canal but, occasionally, it may extend posteriorly to involve significant portions of the anterior hard palate.

The nasopalatine duct cyst (NPC), first described by Meyer in 1914, [1,2] has been defined by the World Health Organization (WHO) as a developmental, epithelial, non-odontogenic cyst. [3] During the fetal period, an epithelial duct, the nasopalatine duct (NPD), exists as a communicator between the nasal and oral cavities. The duct probably served an olfactory function in primitive life. [4,5] Although present in the fetus, it is mostly obliterated by birth. Remnants of the duct may persist [5-8] and proliferate to form the NPC. The stimulus for the proliferation is believed to be trauma or infection, or it may even develop spontaneously. [2,7,9,10] Surprisingly, patency of the NPD may occasionally exist in adults, and its orifice is usually seen as small bilateral openings on either side of the papilla palatina. [5]

The distinctive heart-shaped radiographic configuration of the NPC is best understood through an appreciation of the anatomy of the incisive canal. At the anterior aspect of the floor of the nasal cavity, on either side of the nasal septum, and in close relation to the septum, the foramina of Stensen are located. Stensen foramina open into the right and left incisive canals. These two canals course downward toward the oral cavity and join together to form the common incisive canal (Figures 1,2).

Figure 1. The Y-shaped anatomy of incisive canal is outlined by wires placed in incisive canal of skeleton’s skull.

Figure 2. Surgical view following removal of another example of nasopalatine duct cyst that involved common incisive canal. Wires have been placed to identify right and left incisive canals.

The common canal then exits on the anterior hard palate just lingual to the maxillary central incisors at the incisive foramen beneath the papilla palatina. Consequently, a funnel-shaped Y anatomy is created. The nasal-to-oral length of the canal is reported to be 10 mm. [4,11] Although there are variations, the right and left incisive canals usually join together in the middle third of the incisive canal’s length as it slants downward and forward from the nasal cavity into the oral cavity. [11] Anatomically, the nasopalatine canal transports the terminal branches of the nasopalatine nerve and sphenopalatine artery. These structures serve to supply sensory innervation and vascularity to the tissues of the anterior hard palate.

Although the NPC can occur in the young, it is seen most frequently in the 30- to 60-year age category, [1,8,10,12] with males slightly more susceptible than females. [2,8,10] Usually, the NPC is radiographically visualized as a heart-shaped radiolucency occupying the incisive foramen area (Figure 3). Its unique pattern results from the cyst’s growth conforming to the configuration of the Y anatomy of the incisive canal, plus the resistance offered superiorly by the anterior nasal spine.

Inferiorly, the NPC has a tapered contour, because lateral expansion is frustrated by the roots of the central incisors. The normal radiographic width of the incisive foramen has been reported to be 6 mm. [4,8,11,13] Lucencies > 6 mm should be viewed with suspicion. Pathologic involvement by an NPC is assumed if the width exceeds 10 mm. [11] If radiologic differentiation of a normal foramen from an NPC becomes a problem, periodic observation will reveal an enlarging lucency when an NPC is present. Obviously, the lucency of an incisive foramen is static.

Figure 3. Periapical radiograph illustrates heart-shaped lucency of another example of a nasopalatine duct cyst.

Courtesy Dr. Elizabeth Philipone

The NPC is asymptomatic unless secondarily infected. The cyst usually is diagnosed incidentally during a routine dental radiographic examination. Pain with a suppurative discharge may develop if the cyst becomes infected. Occasionally, the patient may notice a salty taste as cystic contents are discharged through any existing patent NPD orifice. [8]

A tentative clinical diagnosis of an asymptomatic NPC can be made from its radiographic location, size, shape and its nondental involvement. However, substantiation must be obtained from a microscopic examination of the cystic wall. The type of epithelium that lines the cyst wall is determined mainly by the portion of the NPD from which the cyst originates. Proliferation of NPD remnants in the canal closer to the nasal cavity will produce a cyst lined by respiratory epithelium, while cysts arising from remnants closer to the oral cavity will be lined by stratified squamous epithelium. Cysts developing from NPD debris in the mid portion of the incisive canal will have a cuboidal or columnar epithelial lining. [7,8,12] However, mixed epithelial linings are always a possibility. Swanson’s review of 334 NPCs indicated that respiratory epithelium was present in only 28% of the cases. [9] Histologically, the cyst’s fibrous wall contains nerve tissue, blood vessels and mucous glands. [7] A significant inflammatory presence in the cyst’s wall also has been observed in many of the studied cases. [2,7]

Although the vast majority of NPCs demonstrate the described standard signs and symptomatology, unusual manifestations may develop and present diagnostic problems. Occasionally, an NPC can enlarge to extend beyond the incisive foramen region and progress posteriorly to involve significant portions of the hard palate. Previously, these lesions were thought to represent midline fissural cysts that developed from ectoderm trapped during the embryonic fusion of the palatal processes. [14] However, the WHO now considers these cysts to be posterior extensions of an NPC. [15] The authors have treated such a large palatally located cyst and because of its relative rarity, wish to call the profession’s attention to its existence and character.

Case Report A 42-year-old male, in excellent health, was seen in the oral surgery clinic of the Columbia University College of Dental Medicine. His chief complaint concerned the presence of a painless swelling involving the anterior hard palate (Figure 4). He said he became aware of the swelling approximately one year ago, but sought no attention because it was asymptomatic. It was the insistence of his general dentist, during a routine dental examination, that initiated his decision to seek care.

The clinical examination revealed an asymptomatic midline swelling, measuring 2.5 cm in diameter, that involved the middle portion of the anterior half of the hard palate. The overlying mucosa was normal in appearance. No pain was elicited when the swelling was palpated, but some fluctuation was noted. No dental pathology was present. All maxillary anterior and premolar teeth were found to be vital when tested. The radiographic examination, periapical (Figure 5) and occlusal, demonstrated a large, well-defined midline radiolucency that involved the anterior hard palate. Fine-needle aspiration of the swelling produced approximately .75 ml of cyst-like fluid.

Figure 4. Palatal swelling caused by nasopalatine duct cyst.

Figure 5. Periapical film demonstrating large lucent nasopalatine duct cyst with palatal involvement.

Figure 6. Surgical view of palatal bone destruction caused by nasopalatine duct cyst.

A decision to surgically remove the lesion was made. Via local infiltration anesthesia, a palatal flap was mobilized extending from the left premolar area to the right premolar region. A cyst membrane was visualized in contact with the palatal mucoperiosteum. During the flap’s retraction, the cyst membrane ruptured and cystic fluid escaped. Curettage successfully removed the collapsed cystic sac from its bony palatal crypt. Invasion of the nasal cavity was not observed. Anteriorly, the cyst burrowed under a narrowed bridge of intact palatal bone lingual to the central incisors and involved the common incisive canal (Figure 6), but it did not involve the roots of the maxillary central incisors. Upon removal of the pathologic cyst membrane, the palatal flap was reflected and sutured back to its normal position. Healing was rapid and uneventful.

Histologically, stratified squamous epithelium was seen lining the wall of the cystic lesion (Figure 7). A diagnosis of a nasopalatine duct cyst was made.

Figure 7. Microscopic view of nasopalatine duct cyst with stratified squamous epithelium lining (H and E stain, magnification X 100).

Discussion

The temptation to diagnose this case as a median palatine cyst was negated by the surgical observance of the anterior extension of the cyst membrane into the incisal canal. Again, it must be emphasized that the WHO considers these symmetrical midline palatal cysts to represent posterior extensions of an NPC. Our surgical intervention confirmed the cyst’s relation to the incisive canal from which it originated anatomically. It justified the WHO’s classification of these cystic entities as elaborations of an NPC.

Surgery for the NPC, involving the narrow confining limits of the incisal canal, tends to compromise the nasopalatine nerve.

Because of the extensive involvement of the incisal canal, the surgical removal of this large cystic lesion inevitably implicated the closely approximated nasopalatine nerve. Sensory loss in the anterior hard palate can occur in about 10% of NPC patients. [3,16] However, the loss is ameliorated by the anterior extension of the greater palatine nerve, and the finding that the nasopalatine nerve only innervates a limited area of the anterior hard palate. [17,18]

Our case varied from the NPC norm. The usual heart-shaped radiolucency in the midline of the anterior maxilla was not present because the NPC took the option to extend palatally rather than choose the more common incisal canal pathway of least resistance. Therefore, final diagnosis was only confirmed when the clinical and surgical observations were integrated with the microscopic study.

Treatment The NPC, like most cysts, lends itself to routine enucleation. Because of its location, well-defined wall and its non-invasive nature, the NPC can usually be treated successfully via a palatal approach. Recurrences are rare. Marsupialization has been suggested in those select cases that extensively destroy palatal bone and/or compromise the nasal mucosa. [2,3,8]

Queries about this article can be sent to Dr. Mandel at lm7@columbia.edu.

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Jamie Larmie, B.S., is a research assistant and fourth-year student at Columbia University College of Dental Medicine, New York, NY.

Dr. Mandel

Louis Mandel, D.D.S., is director of the Salivary Gland Center and associate dean, clinical professor (OMFS), Columbia University lege of Dental Medicine, New York, NY.