Nasopalatine duct cyst (Incisive Canal Cyst)

Overview


Incisive Canal Cyst are also known as Nasopalatine duct cysts (NPDCs) are developmental, epithelial, nonneoplastic cysts that are considered to be the most common (32.8-73.2%) of the nonodontogenic cysts. Nasopalatine duct cyst is one of many pathologic processes that may occur within the jawbones, but it is unique in that it develops in only a single location, which is the midline anterior maxilla. Nasopalatine duct cysts usually present as unilateral pathology, but they may also occur bilaterally (approximately 0.25% of all cases).

Pathophysiology


The development of the face and the oral cavity takes place between the fourth and eighth weeks of intrauterine life. The secondary palate is formed during the eighth and 12th weeks. In the midline between the primary and secondary palates, 2 channels (the incisive canals) persist. The palatine processes probably partly overgrow the primary palate on either side of the nasal septum. Thus, the incisive canals represent passageways in the hard palate, which extend downward and forward from the nasal cavity. Just before exiting the bony surface of the hard palate (incisive foramen or incisive fossa), the paired incisive canals usually fuse to form a common canal in a Y shape. Nasopalatine canal evaluated by cone-beam CT scanning can be classified into 3 groups: type I (a single canal), type II (2 parallel canals), and type III (Y-type canal).


The fusion of facial processes in the embryologic development of the maxilla results in the formation of a pair of epithelial strands (the nasopalatine ducts) that traverse the incisive canals downward and forward, connecting the nasal and oral cavities. The nasopalatine duct leads from the incisive fossa in the oral cavity to the nasal floor, in which it ends in the nasopalatine infundibulum.


The types of epithelia that line the nasopalatine duct are highly variable, depending on the relative proximity of the nasal and oral cavities. The most superior part of the ducts is characterized by a respiratory-type epithelial lining. Moving downward, the lining changes to cuboidal epithelium. In the most inferior portion closest to the oral cavity, squamous epithelium is the usual type. In addition to the nasopalatine ducts, branches of the descending palatine and sphenopalatine arteries, the nasopalatine nerve, and mucus-secreting glands are present within the incisive canals. In some vertebrates (eg, snakes), the nasopalatine duct plays a role in the reception of odorants.


The nasopalatine ducts ordinarily undergo progressive degeneration; however, the persistence of epithelial remnants may later become the source of epithelia that gives rise to a nasopalatine duct cyst, from either spontaneous proliferation or proliferation following trauma (eg, removable dentures, dental implant treatment), bacterial infection, or mucus retention. Genetic factors have also been suggested.


The mucous glands present among the proliferating epithelium can contribute to secondary cyst formation by secreting mucin within the enclosed structure. Nasopalatine duct cysts can form within the incisive canal, which is located in the palatine bone and behind the alveolar process of the maxillary central incisors, or in the soft tissue of the palate that overlies the foramen, called the cyst of the incisive papilla.

 


What is the prevalence of nasopalatine duct cyst?


Data concerning the prevalence of nasopalatine duct cysts differ considerably, with rates of 0.08%. to 33%. having been reported. Nasopalatine duct cysts account for approximately 12% of all jaw cyst tumors. They occur in both black and white populations. During last 50 years in the English-language literature, fewer than 500 cases have been published.


International


In a Turkish study, of12,350 patients studied, 452 odontogenic cysts (98.5%) and seven nonodontogenic cysts (1.5%) were found; all the nonodontogenic cysts were nasopalatine duct cysts. In a Brazilian autopsy study of 10,311 oral biopsy specimens, 58 met the criteria for nonodontogenic cysts, 19 of which were nasopalatine duct cysts.


Race
No racial predilection is known. Nasopalatine duct cysts that occur in young Afro-Caribbeans appears to be more clinically aggressive than those that occur in other ethnic groups.

Sex
Males are affected 1.1-20 times more often than females, although the predilection for males is not so obvious in all studies.


Age
Nasopalatine duct cysts occur over a wide age range (7-90 y), and they also occur in fetuses. Most patients who are affected are aged 30-60 years, a with mean age of 46.2 years.

Clinical presentation
Most patients are symptomatic. They present as swelling of anterior palate, sometimes associated with pain and drainage. They must usually be larger than 0.6 cm to distinguish cyst from incisive foramen, which is a normal anatomical feature.

Pathology
Cyst formation is due to spontaneous cystic degeneration of residual ductal epithelium. The vast majority of cases contain non-keratinized stratified squamous epithelium alone or in combination with other epithelia histologically. Approximately 30% cases contain repiratory epithelium 3.

Radiographic features
They are seen as a solitary well-defined, oval or round unilocular radiolucency, between central incisors, >0.6 cm in diameter. They may appear “heart-shaped” if the anterior nasal spine superimposed. Root resorption and tooth displacement may be present.

MRI
Usually shows homogeneous high signal intensity on both on T1 and T2, although most cysts of maxillofacial regions demonstrate low to intermediate signal intensity on T1 weighted images 1.

Treatment and prognosis
Enucleation is usually curative, and recurrence is rare. Histological confirmation is recommended.

Differential diagnosis
General imaging differential considerations include:

  • periapical granuloma/periapical cyst
  • schwannoma in the incisive canal region
  • nasolabial cyst
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