Nasopalatine Duct Cyst 

Updated: Aug 30, 2017
Author: Piotr Kurnatowski, MD; Chief Editor: Dirk M Elston, MD 

Overview

Background

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.[1, 2] 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).[3]

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.[4] 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).[5]

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.[6]

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.[4, 7, 8] In some vertebrates (eg, snakes), the nasopalatine duct plays a role in the reception of odorants.[9]

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[4, 10, 11, 12] or proliferation following trauma (eg, removable dentures, dental implant treatment),[13] bacterial infection, or mucus retention.[4, 11, 14, 15, 16]

Genetic factors have also been suggested.[11, 17]

The mucous glands present among the proliferating epithelium can contribute to secondary cyst formation by secreting mucin within the enclosed structure.[18] 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.[19]

Epidemiology

Frequency

United States

Data concerning the prevalence of nasopalatine duct cysts differ considerably, with rates of 0.08%.[20] to 33%.[21] having been reported. Nasopalatine duct cysts account for approximately 12% of all jaw cyst tumors.[22] They occur in both black and white populations.[14] During last 50 years in the English-language literature, fewer than 500 cases have been published.[23]

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.[24] 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.[2]

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.[11]

Sex

Males are affected 1.1-20 times more often than females,[1, 18, 25, 26, 27] although the predilection for males is not so obvious in all studies.[2, 11, 28, 29, 30]

Age

Nasopalatine duct cysts occur over a wide age range (7-90 y), and they also occur in fetuses.[2, 14, 31] Most patients who are affected are aged 30-60 years, a with mean age of 46.2 years.[1, 2, 10, 32, 33, 34]

Prognosis

Complete postsurgical bony regeneration is expected in most patients. After surgical treatment, recurrence is uncommon, having been reported in 0-11% of patients.[8, 19, 28, 30] Only two cases of malignant change in the lining epithelium of a nasopalatine duct cyst have been published.[35, 36]

 

Presentation

History

The cyst dimensions have no correlation to preoperative symptoms.[5]

Small cysts in the early stages of their development are frequently (40-87%) asymptomatic and are likely to be recognized on routine radiographic examinations during dental treatment.[7, 8, 14, 22, 26, 28, 29, 31, 37]

Large cysts can be responsible for a variety of symptoms, including swelling in the anterior part of the midline of the palate (52-88%), discharge (25%), pain defined as a burning sensation in the anterior part of the maxilla that occasionally radiates into the bridge of the nose, and in a person who wears a dental prothesis, a pressure sensation underneath the prosthesis (20-23%); secondly, tooth movement can occur. The pain also can be caused by super infection. About 70% of patients experience a combination of these symptoms. Sometimes, fistula formation or an inability to wear dentures is observed.[14, 22, 23]

Paradoxically, patients with small cysts may have disproportionately severe symptoms, whereas patients with large ones may experience few or no symptoms. In all cases in which there is an expansion of the cyst into nasal cavity, symptoms are more severe.[5]

A salty taste in the mouth and devitalization of the pulps of associated teeth have been reported.[19, 30, 38]

Physical Examination

Large and more destructive cysts that have perforated the labial and palatal bony plates may present as expansile, fluctuant swellings of the anterior palate and the palate.

Extrabony cysts that develop within the soft tissues of the incisive papilla area of the anterior hard palate (called the cyst of the incisive papilla) may present as a translucent or bluish colored, dome-shaped swelling. The clinically apparent discoloration is due to the accumulation of fluid contents within the cyst.

Nasopalatine duct cysts clinically demonstrate slow and progressive growth, sometimes exceeding 60 mm in diameter.

Tooth displacement is a common finding, having been reported to occur in 78% of patients,[28, 39] whereas bony expansion is noted in only 1.4% of patients.[28] The literature describes an untreated case that caused destruction of bone and mucosa and movement of teeth, with ensuing disability.[40]

Usually, the anterior teeth react positively to pulp sensitivity testing. In some cases when the electric pulp test is negative or when endodontic treatment has already been performed in the incisor region, the correct diagnosis is more difficult.[41]

Causes

The cause of nasopalatine duct cyst is essentially unknown; in most cases nasopalatine duct cysts are idiopathic.[42] Trauma, infection, and mucous retention within associated salivary gland ducts have all been suggested as possible pathogenetic factors; however, most believe that spontaneous cystic degeneration of residual ductal epithelium is the most likely etiology.[7, 43]

Cases of cyst developed after dental implant placement have been described.[44]

 

DDx

Diagnostic Considerations

A well-circumscribed, heart-shaped, midline radiolucency that is inter-radicular in location between the roots of vital maxillary incisor teeth is virtually pathognomonic for nasopalatine duct cyst; however, other benign entities that develop within the jawbones with some frequency, such as the following, can mimic nasopalatine duct cyst and should be considered in the clinical differential diagnosis[45] :

  • Odontogenic cysts (eg, lateral radicular cyst, lateral periodontal cyst, odontogenic keratocyst)

  • Odontogenic tumors (eg, ameloblastoma, odontogenic myxoma)

  • Nonodontogenic tumors (eg, central giant cell tumor, brown tumor of hyperparathyroidism, central hemangioma, granuloma)

  • Osteitis fistulizing in the palatine direction or a bucconasal and/or buccosinusal communication.[23, 42]

Additional diagnostic procedures (see Workup) can be helpful in further limiting this list to a working diagnosis of nasopalatine duct cyst.

Differential Diagnoses

 

Workup

Imaging Studies

Panoramic, occlusal, and periapical radiographs are standard in the radiographic evaluation of suspected nasopalatine duct cyst. A radiological examination in a minimum of 2 projections (periapical and occlusal) should be performed.[23] In some cases, obtaining a 3-dimensional view of the lesion may be necessary.

CT scanning

Harris and Brown[46] advocate a second periapical radiograph taken perpendicular to the first, a CT scan (shows imaging information as direct axial or coronal slices or as reformatted coronal or sagittal slices), and linear tomography through the area of interest in an alternative plane.

In 2000, Pevsner et al[47] reported CT scan characteristics believed to be unique to nasopalatine duct cysts. These include (1) a midline position of the lesion; (2) pressure erosion of the tooth apices and exclusion of contiguous tooth numbers 8 and 9 rather than incorporation of the apices of these teeth within the cyst; and (3) smooth, noninflammatory bony expansion of the lesion with sclerotic margins. The expansile change of the posterior midline maxilla and smooth elevation of the nasal cavity with tilting of the nasal septum suggest a long-term process that is likely developmental and consistent with a nasopalatine duct cyst.

In 2011 Suter et al applied cone-beam CT scanning to describe nasopalatine duct cysts.[5]

MRI

MRIs of nasopalatine duct cysts show homogeneous high-signal intensity on T2-weighted images and intermediate signal intensity on T1-weighted images in the area of the contents of nasopalatine duct cysts (keratin and viscous fluids). MRI is more specific than CT.[32, 22, 37, 48, 49]

Radiography

Radiographic examination typically discloses a well-defined, ovoid, round or inverted, pear-shaped radiolucency located in the midline of the maxilla, which is inter-radicular and apical to the roots of the maxillary central incisor teeth; larger lesions resorb the surrounding maxillary cortex.[37]

The mean radiographic diameter is reported to be 17.1 mm.[19, 28] The mean cyst surface area reportedly is 566 mm2 (84-4,516 mm2), and the mean cyst volume is reported to be 1,735 mm3 (65-25,350 mm3).[50]

Superimposition of the nasal spine can impart a heart-shaped appearance to the cyst.

Peripheral sclerosis, an indication of a slowly developing growth and intrabony expansion, may or may not be present. The roots of the central incisors may show divergence.

Destruction of the floor of the maxillary antrum has been described.[39]

In some individuals, a prominent incisive canal can appear as a radiolucent area and mimic nasopalatine duct cyst.

Most authors agree that 6 mm should be considered the upper limit for a normal incisive canal. Radiolucencies larger than this should be considered potentially pathologic and merit further investigation.[28]

Note the images below.

An ovoid radiolucent area between the central inci An ovoid radiolucent area between the central incisor teeth with a poorly defined sclerotic outline can be suspected to be a cyst.
An ovoid, clearly radiolucent area with a sharply An ovoid, clearly radiolucent area with a sharply defined outline and sclerotic margin that has a bearing on the teeth appendix; secondary draw aside of incisor roots.
An ovoid radiolucent area with a poorly defined sc An ovoid radiolucent area with a poorly defined sclerotic outline between the central incisor teeth.

Procedures

Aspiration of pathologic jaw radiolucencies can provide useful information in distinguishing solid processes from cystic processes but is not itself diagnostic of an entity. A clear or straw-colored fluid aspirate is suggestive of nasopalatine duct cyst; however, other cystic processes (eg, lateral radicular cyst, cystic ameloblastoma) cannot be excluded on the basis of this finding alone. Bloody fluid is more indicative of a central hemangioma, a central giant cell lesion, an arteriovenous malformation, or an aneurysmal bone cyst. Negative aspiration indicates a solid process (eg, odontogenic myxoma, solid ameloblastoma).

Tooth vitality testing may be necessary. In the absence of caries, traumatic injury, or other obvious cause of pulpal necrosis, the adjacent maxillary central incisor teeth should be vitality tested to exclude the possibility of a pulpal-periapical inflammatory pathogenesis (eg, lateral radicular cyst, dental granuloma, periapical cyst, periapical abscess).

Histologic Findings

Histopathologic examination discloses a cavity lined by epithelium and surrounded by a connective tissue wall. A reported about 70% of nasopalatine duct cysts have squamous, columnar, cuboidal, or some combination of these epithelial types; respiratory epithelium is seen in 9.8-32.0%.[19, 28, 31, 42] The type of epithelium depends on the localization of the cyst (see Pathophysiology), and it may also be reflective of the pluripotential character of the embryonic epithelial remnants.[17] Rarely, dendritic melanocytes have been reported within the epithelium.[51] Malignant transformation of the lining epithelium has not been reported.[33]

Often (81% of cases), a chronic inflammatory reaction consisting of lymphocytes and plasma cells is observed in the cyst wall; hemorrhage has been noted in 71% of cases.[26] Also helpful in the microscopic diagnosis of nasopalatine duct cyst are the presence of structural elements in the cyst wall that are native to the nasopalatine canal (eg, moderately sized peripheral nerves, arteries and veins, mucous glands, adipose tissue).

For the correct diagnosis, immunohistochemistry can be used. Immunohistochemical profiles for K7, K13, MUC-1, and P63 are useful.[52]

The cyst can be filled by semisolid material, containing erythrocytes, leukocytes, desquamated epithelial cells, tissue debris, and bacteria.[1, 4]

 

Treatment

Surgical Care

Nasopalatine duct cysts are treated by enucleation via a palatine or buccal approach; transnasal endoscopic marsupialization can also be applied.[53, 54]

Recurrence is uncommon, having been reported in 0-11% of patients.[19, 28, 30]

If components of the long sphenopalatine nerve are removed during surgery, it may cause paresthesia to the anterior palate.[29, 30]

Complete bone regeneration within the bony defect is expected postoperatively.

In some cases, a marsupialization is necessary, such as when the capsule shows adhesion with the surrounding area and enucleation is difficult to perform.

Complications

Very large, untreated nasopalatine duct cysts may resorb the roots of the adjacent teeth and display the roots. Other complications may include perforation of the vestibular bone, nasal cavity, and maxillary sinus[55] ; a large cyst can cause complete destruction of the anterior palate and pyriform rim.[56] Paresthesia to the anterior palate may occur in 10% of cases if components of the long sphenopalatine nerve are removed or damaged during surgery.[23, 29, 30] In addition, devitalization of central incisors, postoperative wound infection, and postoperative fistula can occur.[5] There is a statistically significant correlation between the presence of postoperative and late complications with cyst diameter, surface area, and volume.[50]