Nasopalatine Canal Masquerading as a Periapical Cyst

Abstract

The incisive foramen is also called as nasopalatine foramen. It is a funnel-shaped opening in the anterior maxilla which opens immediately behind the central incisor teeth through which nasopalatine blood vessels and nerves pass. The incisive foramen is continuous with the incisive canal or nasopalatine canal (NPC). Variations in size, shape, position, and number of NPCs exist. Anatomical variations in NPC cannot be appreciated on two-dimensional radiographs. A case of anatomical variation of the nasopalatine canal misdiagnosed as a periapical cyst is discussed.

Introduction

The nasopalatine canal (NPC) is also called as the anterior palatine canal or incisive canal. It was first coined by Ad Stenson in 1683. It is located in the anterior maxilla behind the maxillary central incisors connecting the roof of the oral cavity and the floor of the nasal cavity. In the oral cavity, the NPC opens through the incisive foramen beneath the incisive papilla and opens in the nose through the foramina of Stenson, which are usually two in number. Through each of them passes the terminal branch of the descending palatine artery and the nasopalatine nerve, to communicate with the posterior septal branch of the sphenopalatine artery and greater palatine nerve, respectively.[1] Before any surgical procedure in the anterior maxilla such as administration of local anesthesia, placement of implants, and enucleation of cysts, it is essential to know about the morphology of NPC and its variations.[2] Two-dimensional images such as intraoral periapical radiographs and orthopantomographs are not able to appreciate the variations in NPC. Cone-beam computed tomography (CBCT) plays a vital role in diagnosing the variations of NPC. CBCT helps in the evaluation of anatomical variations in a three-dimensional view to prevent misdiagnosis.

Case Report

A 43-year-old man reported chief complaints of pain in the right upper maxillary tooth that was present for 1 month. A diagnosis of periapical cyst in relation to the right upper anterior teeth (11 and 21) was diagnosed based on intraoral radiographs [Figure 1]. On electric pulp testing, 11 and 21 remain vital. Endodontic treatment was performed for 11, but pain did not subside. CBCT of the maxilla was taken with the following parameters (Planmeca ProMax three-dimensional [3D] classic with the following parameters: 90 kvp, 4–10 ma, 200 μm voxel size). The measurements were performed using Planmeca Romexis 5.1.0.r software (Helsinki, Finland).

Figure 1.

Intraoral periapical radiograph showing the presence of periapical radiolucency between 11 and 21

In the coronal section, there was an evidence of enlarged NPC between 11 and 21 with increased oral opening of NPC [Figure 2a]. In the axial section, the size of the NPC was enlarged in anteroposterior and mediolateral directions and it measured 7.65 mm × 6.47 mm [Figure 2b]. According to Shear and Speight,[3] a radiographic shadow with anteroposterior dimension of as much as 10 mm in the incisive fossa region may be within the normal limit. However, Bodin et al.[4] proposed that if the radiolucency had a width exceeding 8 mm more pronounced, and had a thin cortical border on the periphery, exploratory surgery should be considered, especially if the lesion was asymmetrically bulging, and that radiolucencies exceeding 14 mm in diameter were always cysts. In the sagittal section, the shape of the nasopalatine canal was spindle shaped [Figure 2c].

Figure 2.

(a) Coronal section showing enlarged nasopalatine canal with increased oral opening. (b) Axial section showing the measurement of enlarged nasopalatine canal. (c) Sagittal section showing the spindle shape of nasopalatine canal

In the sagittal section, the measurements of NPC opening in the nasal floor and oral opening were observed. The distance between the anterior wall of NPC and the labial cortex was observed at palatal, middle, and nasal levels. The distance between the posterior wall of NPC and the palatal cortex was observed at palatal, middle, and nasal levels [Figure 3a]. The measurements of NPC justified that it was only a variation of NPC and not a periapical cyst in relation to 11 and 21.

Figure 3.

(a) Sagittal section explaining the measurements of nasopalatine canal (NPC) and its surrounding structures. (b) Sagittal section showing the volume of NPC in this patient. (c) Three-dimensional view of enlarged nasopalatine canal

The volume of NPC was measured as 1.267 cm³ in the sagittal section with the help of specialized Romexis software [Figure 3b]. It clearly showed only a variation of NPC with this volume. It distinguished the cystic volume and the normal variation of NPC. By this volume, we can easily prevent misdiagnosing variation of NPC as a periapical cyst in this region. A reconstructed 3D image of CBCT showed the variation of the presence of an enlarged nasopalatine canal in 11 and 21 regions [Figure 3c].

Discussion

NPC is an important anatomical structure which is present between the 11 and 21 regions of the anterior maxilla. There are a lot of variations in NPC such as position, number, shape, and size. In normal two-dimensional X-rays, we are not able to appreciate these variations. Since NPC carries neurovascular structures, it might be damaged during any surgical procedure. In this case report, the case was initially misdiagnosed as a periapical cyst in the 11 and 21 regions. However, CBCT confirmed it to be an anatomical variation.

Song et al.[5] evaluated the NPC variations in its shape as widened or spindle shaped, very large, and narrowed. Begum and Ahmed[6] conducted a study in 2019. In that study, the cylindrical shape of NPC was the most common type and the spindle shape was the least common type. In our case report, the shape of NPC was spindle shape.

The mean length of the NPC in males was 12.04 mm, and in females, it was 10.76 mm. In our male patient also, the length of NPC was measured as 12.01 mm which was consistent with the studies done by Kajan et al.[7] which was 12.84 ± 2.88. Mraiwa et al.[8] reported that the diameter of the canal ranged from 1.5 mm to 9.2 mm. They also estimated the mean diameter of the NPC on the palatal side (4.6 mm), which was consistent with our patient measurements.

Gopal and Kapoor[9] reported that the mean labial cortical bone at palatal, middle, and nasal levels was 6.22 ± 1.73 mm, 6.9 ± 1.87 mm, and 13.48 ± 41.82 mm, respectively. The mean palatal cortical bone at palatal, middle, and nasal levels was 2.87 ± 0.78 mm, 4.48 ± 1.06 mm, and 6.22 ± 1.67 mm, respectively; these results were consistent with our case report which ranges from 1.91 mm to 6.91 mm.

Nemtoi et al.[10] reported the mean volume of NPCs. The maximum value obtained was 1.27 cm³ and the minimum was 0.27 cm³ which was consistent with our case wherein the 3D volume of NPC was 1.267 cm³.

Conclusion

NPC shows enormous variations in size, shape, curvature, angulation, and dimensions. Conventional 2D images are not able to replicate the original anatomy of NPC. Only with CBCT, we can understand the true anatomical variations to prevent neurovascular damage from surgical procedures and implant placements and in the assessment of any pathology in the anterior maxilla. This case report has emphasized the importance of CBCT in evaluation of the true color of neurovascular anatomical variation of NPC misdiagnosed as a cyst.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.