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Her medical and surgical histories were noncontributory and she was not taking any medications. The patient stated that she was a nonsmoker and drank alcohol socially; she reported no history of trauma to her anterior teeth.

Physical examination revealed facial tenderness and expansion of the anterior maxilla, with palatal swelling in the approximate midline. The patient had no cervical or submandibular lymphadenopathy. Teeth No. 8–10 did not reveal caries or restorations; however, these teeth tested nonvital to electrical stimulation.

A panoramic radiograph and conebeam computed tomography (CBCT) scan were obtained, revealing a radiolucent lesion (4–5 cm) in the midline of the anterior maxilla (Fig. 2). Figure 3 is a skeletal reconstruction view of the CBCT image.

An excisional biopsy (together with enucleation and curettage) under general anesthesia was planned; if intraoperative findings dictated, an incisional biopsy would be performed. A palatal splint was fabricated preoperatively. A sulcular incision was used to approach the lesion. A mucoperiosteal flap was reflected labially and palatally to gain access to the lesion (Fig. 4). At that time, it was noted that the lesion had eroded through the midline anterior palate and the anterior nasal spine, shifting the nasal floor superiorly. The lesion was dissected carefully and lifted off the nasal floor (Fig. 5 and 6). Manipulation led to the extrusion of a brownish fluid from the lesion. The prefabricated palatal splint was wired to the bilateral first premolars and central incisors to support the tissue and prevent hematoma formation (Fig. 7). The specimen was sent for histopathologic examination. The patient recovered uneventfully and was referred to her general dentist to evaluate the status of her anterior teeth.

Differential diagnosis

In the present case, it initially was assumed that the patient had a periapical pathology, such as a periapical abscess. Periapical abscesses result from the accumulation of inflammatory cells, usually at the apex of nonvital teeth. Teeth No. 8–10 all were found to be nonvital. Periapical abscesses typically manifest as ill-defined radiolucencies; however, the patient’s panoramic radiograph revealed a well-circumscribed radiolucency.¹

A periapical abscess might develop into a periapical granuloma and later into a periapical cyst. Radiographically, both periapical granulomas and cysts are marked by a loss of lamina dura and possible root resorption.^1,2 In the present case, neither of these symptoms was seen.

Periapical cemental dysplasia (PCD) occurs most commonly in black women, which should be considered in the differential diagnosis.¹ PCD may begin as a radiolucency, but it becomes a mixed radiolucency and radiopacity over time. It typically appears in the mandibular anterior dentition. In addition, a PCD generally is asymptomatic; by contrast, the patient in the present case complained of moderate pain.^1,3

The midline palatal and labial mucosal fluctuant swelling seen in the present case suggests a nasopalatine duct cyst, which typically is associated with pain and a well-circumscribed radiolucency near the midline of the anterior maxilla; however, a definitive diagnosis cannot be made without a histopathological examination.⁴

While a nasopalatine duct cyst might have appeared to be the likely diagnosis, other lesions cannot be excluded. A 2005 article by Yih and Krump reported a rare case of an odontogenic keratocyst in the nasopalatine duct.⁵ An odontogenic keratocyst also manifests as a well-defined radiolucency, although these lesions usually are asymptomatic and are located in the posterior mandible.⁶

Adenomatoid odontogenic tumors (AOTs) also occur as unilocular radiolucencies in the anterior maxillary region; however, like dentigerous cysts, AOTs usually are asymptomatic and are associated with an impacted canine.^1,7,8 The lesion in the present case was symptomatic and was not associated with any impacted teeth, making both AOT and dentigerous cyst highly unlikely.

Other possibilities included central giant cell granuloma and ameloblastoma, both of which can appear as unilocular or multilocular radiolucencies. However, these lesions usually are asymptomatic and are located in the mandible, in contrast to the patient’s symptomatic lesion in the anterior maxilla (see the table).

Discussion

The nasopalatine duct cyst is the most common nonodontogenic cyst in the oral cavity.⁹ This lesion also is known as an anterior middle cyst, maxillary midline cyst, anterior middle palatine cyst, and incisive canal cyst.⁴ This cyst is believed to arise from remnants of the nasopalatine duct, an embryologic structure that connects the oral and nasal cavities in the area of the incisive canal.¹ The nasopalatine duct undergoes progressive degeneration in humans but may leave epithelial remnants behind; these remnants may become the source of epithelia that lead to the nasopalatine duct cyst. Possible etiologic factors include trauma (for example, removable dentures), bacterial infection, mucous retention, genetic factors, and spontaneous proliferation.^9,10

The incisive canal begins on the floor of the nasal cavity (on either side of the nasal septum), coursing downward and forward to exit the palatal bone by a common foramen in the area of the incisive papilla. The cyst may develop at any age in this canal but is most common between the ages of 30 and 59.^11,12 The most common symptoms include swelling of the anterior palate, drainage, and pain.^11,13 On rare occasions, the cyst may produce a fluctuant expansion involving both the anterior palate and labial alveolar mucosa, as seen in the present case.¹

Radiographs are a valuable adjunct to diagnosing a nasopalatine duct cyst, as they usually demonstrate a well-circumscribed radiolucency near the midline of the anterior maxilla, between and apical to the central incisors.¹² Cysts may develop a pear- or heart-shaped morphology due to resistance of the adjacent teeth.¹ It is unusual that a larger than average cyst—such as that found in the present case—would extend from the anterior palate to the labial alveolar mucosa without significant displacement/divergence of the central incisors.

In 1938, Roper-Hall concluded that any radiographic lesion with a diameter of less than 6 mm should be considered within normal limits, based partially on finding that the diameter of the average incisive foramen was approximately 3 mm.¹⁴ In the present case, however, the lesion was well over 6 mm in diameter.

In 2000, Pevsner et al reported CT scan characteristics unique to the nasopalatine duct cyst, including a midline position of the lesion; pressure erosion of the tooth apices and exclusion of contiguous teeth No. 8 and 9, rather than the apices of these teeth being incorporated within the cyst; and smooth, noninflammatory bony expansion of the lesion with sclerotic margins.¹⁵

Histologically, the type of epithelial lining of a nasopalatine duct cyst varies, depending on location.⁴ Cysts near the nasal cavity are likely to contain pseudostratified columnar (or respiratory) epithelium (Fig. 8), while those located near the oral cavity are likely to contain squamous epithelium (Fig. 9).¹ Frequently, a cyst contains more than one epithelial type (Fig. 10). Stratified squamous epithelium is most common, followed by pseudostratified columnar epithelium.¹ A 1981 study by Allard et al examined 334 cases and noted that 71.8% of nasopalatine duct cysts have either squamous, columnar, or cuboidal epithelium; in addition, 9.8% of patients showed respiratory epithelium alone while 18.2% had both respiratory and squamous epithelium. The type of epithelium was not related to the cyst size.⁹

Most of the lesions listed above, with the exception of ameloblastoma, are treated by enucleation and curettage, while nasopalatine duct cysts may be treated by enucleation via a palatine or labial approach. In the present case, the approach was made both palatally and labially due to the size of the lesion, although enucleation and curettage remained the objective of treatment. A 2004 article by Elliott et al concluded that low recurrence rates made enucleation the preferred treatment.8 Recurrence rates of 0–11% have been reported.¹⁶

As the nasopalatine duct cyst is the most common nonodontogenic cyst in the oral cavity, further research is necessary to investigate its pathogenesis. Given the typical painful manifestation of these lesions, they can cause much grief and distress to patients. Identifying the lesion in its early stages can help to prevent some of the pain, aggravation, and inconvenience that patients would experience otherwise.

Summary

This article emphasizes the importance of a thorough history and physical and radiographic examinations. The history and physical examination allow dentists to determine how long the lesion has been present, the presence of any contributing factors (for example, systemic medical conditions or trauma), and whether the lesion is symptomatic. At the very least, a panoramic radiograph should be taken. Including careful radiographic examination could help dentists to determine whether additional imaging is necessary. All of this information is crucial for proper diagnosis and treatment planning.

Being able to recognize pathology, diagnose it, and treat it properly—whether the dentist performs the surgery or refers it to a specialist—has been one of the most challenging aspects of general dentistry. By diagnosing and treating pathology efficiently, it is possible to provide patients with a much higher quality of life.

Author information

CPT Elyassi is a resident, OMFS PGY2 Program at Tripler Army Medical Center, Hawaii, where COL Closmann is the OMFS Residency program director, COL Baus is the OMFS Residency assistant director, and CDR Torske is an oral and maxillofacial pathologist.

References
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