Nasopalatin duct cysts: Report of ten cases and review of literature

Nasopalatine duct cyst, also known as incisive canal cyst, is the most common among non-odontogenic developmental cysts [1-3]. It occurs in approximately 1% of the population [4]. It was irst described by Meyer in 1914 [4]. Nasopalatine duct cyst, which is more common in 4-6th decades, mostly develops in the midline of the anterior maxilla [5,6]. This cyst is more frequent in male [5]. Most patients are asymptomatic. When they are symptomatic, they present as swelling of anterior hard palate, sometimes associated with pain and drainage [7]. They must usually be larger than 0.6 cm to distinguish cyst from incisive foramen, which is a normal anatomical feature. They are seen as a solitary wellde ined, oval or round unilocular radiolucency, between central incisors, >0.6 cm in diameter [7,8]. They may appear “heart-shaped” if the anterior nasal spine superimposed. Root resorption and tooth displacement may be present. Enucleation is usually curative, and recurrence is rare. Histological con irmation is recommended [7].


Introduction
Nasopalatine duct cyst, also known as incisive canal cyst, is the most common among non-odontogenic developmental cysts [1][2][3]. It occurs in approximately 1% of the population [4]. It was irst described by Meyer in 1914 [4]. Nasopalatine duct cyst, which is more common in 4-6 th decades, mostly develops in the midline of the anterior maxilla [5,6]. This cyst is more frequent in male [5]. Most patients are asymptomatic. When they are symptomatic, they present as swelling of anterior hard palate, sometimes associated with pain and drainage [7]. They must usually be larger than 0.6 cm to distinguish cyst from incisive foramen, which is a normal anatomical feature. They are seen as a solitary wellde ined, oval or round unilocular radiolucency, between central incisors, >0.6 cm in diameter [7,8]. They may appear "heart-shaped" if the anterior nasal spine superimposed. Root resorption and tooth displacement may be present. Enucleation is usually curative, and recurrence is rare. Histological con irmation is recommended [7].

Case reports
We present the case of nasopalatine canal cyst in 10 patients, 8 males and 2 females, aged between 34-66, who applied to Istanbul University Faculty of Dentistry, Department of Oral and Maxillofacial Surgery. We examined the patients in terms of age (years), gender, complaints, radiographic indings and the condition of the teeth involved. Nasopalatine duct cyst was detected on routine radiography in 2 patients, and 2 patients complained of saltwater taste in the mouth. Six patients complained of swelling they felt in the palatinal region ( Figure 1). Panoramic radiography showed heart shaped radiolucent area in 3 patients and 7 patients had oval radiolucent area (Figures 2,3).
When the conditions of the related teeth were evaluated, it was observed that the teeth were devital in 3 patients, the implant was inside the lesion in 1 patient, 1 patient was toothless, and the related teeth were vital in 5 patients (Figures 4,5).
Nasopalatine duct cysts are usually treated by enucleation through the palatinal approach [5]. Surgical enucleation of the cyst is performed under local anesthesia and the result is generally positive when the cyst is aspirated before removal. We enucleated all cysts under local anesthesia (Figures 6,7).
It has a good prognosis. No recurrence was observed in the patients we followed up.

Discussion
Nasopalatine duct cysts, which can be seen at any age, are more common in 4-6 th decades [2]. It is observed three times more frequently in males than in females [2]. In our cases, male patients are the majority and the average age of the patients is 49.4. These results are similar to the literature [5,7,8]. Panoramic radiography, periapical radiography, occlusal radiography and computed tomography can be used in radiological examination [2]. Especially periapical radiographs taken from different horizontal angles facilitate the diagnosis. In this control, the appearance of the nasopalatine canal cyst changes, while the radicular cyst continues to be located at the apex of the central incisors [2,6]. Incisive foramen larger than 6 mm may give the appearance of cysts [8]. Follow-up radiographs should be taken in suspected cases [6]. Nasopalatine duct cyst is well circumscribed, giving a round or oval appearance [6]. The shadow of the nasal spina sometimes can be superposed, causing the cyst to look like a heart shaped [2]. We found mostly oval shaped radiolucent lesions in the cases we presented. Radiographic images of 3 patients have a heart-shaped radiolucent area.
The radiographic image is not always symmetric, it can give the same image as the radicular cyst and periapical granuloma [2,6]. Aparna, et al. presented a case of nasopalatine duct cyst that was mistaken for radicular cyst      Heart shaped radiolucent lesion Edentate and was treated incorrectly. They reported that there were 8 similar cases in the literature [9]. Loss or enlargement of the lamina dural at the apex of the central incisors indicates an in lammatory lesion [2,9]. Vitality test is very important in differential diagnosis. In the nasopalatine duct cyst, the teeth maintain their vitality [3,6,9]. 3 patients whose complaints did not resolve even though their teeth had root canal treatment, applied to our clinic. Nasopalatine duct cysts diagnosed after enucleation. Clinical and radiographic improvement was observed after the enucleation of the cysts. This situation con irms that the related teeth are vital in the nasopalatine duct cyst and can be misdiagnosed radiographically with other periapical pathologies.
Nasopalatine canal cyst is mostly asymptomatic and diagnosed on routine radiography. The most common symptoms are swelling, pain, and drainage of the anterior palate mucosa. Near-surface cysts can cause blue, luctuant swelling in this area. Deep cysts are covered with normal mucosa as long as there is no ulceration. If nasopalatine nerve is pressed, burning and numbness may occur in the area [2].
When it drains into the mouth, patient can feel salty taste. A 66-year-old male patient applied to our clinic complained of the salt water taste he felt in his mouth. After the panoramic radiography, it was observed that the nasopalatine canal cyst was not noticed, and a dental implant was placed into it. There are 4 implant-related nasopalatine duct cyst cases in the literature [10]. In all cases, nasopalatine duct cyst developed after implant surgery [10]. Cyst development in 3 cases was attributed to the traumatization of the nasopalatine duct [11,12]. In one case, it was reported that cellular proliferation might have been induced by infection in the area [13]. In our case ( Figure 5), the nasopalatine canal cyst was not noticed in the radiological examination and the dental implant was placed in the cyst.

Conclusion
Nasopalatine duct cyst is generally asymptomatic and can be detected on routine radiographs. Sometimes, it can cause swelling, drainage or pain in the palatal mucosa. Although panoramic radiography is accepted as the standard in the irst approach to pathological formations in the jaws, the superposed image may mislead the physician. In case of doubt, besides panoramic radiography, auxiliary diagnostic methods such as computed tomography, periapical graphy, vitality test should be used. It must be distinguished from other maxillary anterior radiolucencies to prevent a wrong treatment plan. The inal diagnosis is made as a result of histopathological examination. Enucleation is the preferred treatment method because of its low recurrence rate.