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. [28] In some cases, obtaining a 3-dimensional view of the lesion may be necessary.
CT scanning
Harris and Brown [48] 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 [49] 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. [12]
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. [36, 27, 39, 50, 51]
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. [39]
The mean radiographic diameter is reported to be 17.1 mm. [5, 6] 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). [52]
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. [41]
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. [6]
Note the images below.
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 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 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%. [5, 6, 35, 44] 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. [23] Rarely, dendritic melanocytes have been reported within the epithelium. [53] Malignant transformation of the lining epithelium has not been reported. [37]
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. [32] 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).
A nasopalatine duct cyst was described with sebaceous differentiation. [54]
For the correct diagnosis, immunohistochemistry can be used. Immunohistochemical profiles for K7, K13, MUC-1, and P63 are useful. [55]
The cyst can be filled by semisolid material, containing erythrocytes, leukocytes, desquamated epithelial cells, tissue debris, and bacteria. [1, 11]
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An ovoid radiolucent area between the central incisor teeth with a poorly defined sclerotic outline can be suspected to be a cyst.
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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.
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An ovoid radiolucent area with a poorly defined sclerotic outline between the central incisor teeth.
