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AUTHOR AND EDITOR INFORMATION

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Author: Piotr Kurnatowski, MD, Professor, Department of Otolaryngology, Medical University of Lodz, Poland

Coauthor(s): Deborah Cleveland, DDS, Director of Oral Pathology, Associate Professor, Department of Oral Pathology, Biology and Diagnostic Sciences, University of Medicine and Dentistry of New Jersey; Camila K Janniger, MD, Clinical Professor of Dermatology, Clinical Associate Professor of Pediatrics, Chief of Pediatric Dermatology, New Jersey Medical School

Editors: Jacek C Szepietowski, MD, PhD, Professor and Vice-Head, Department of Dermatology, Venereology and Allergology, Wroclaw Medical University, Poland; David F Butler, MD, Professor of Dermatology, Texas A&M University College of Medicine; Director, Division of Dermatology, Scott and White Clinic; Director Dermatology Residency Training Program, Scott and White Clinic; Robert A Schwartz, MD, MPH, Professor and Head of Dermatology, Professor of Medicine, Professor of Pediatrics, Professor of Pathology, Professor of Preventive Medicine and Community Health, UMDNJ-New Jersey Medical School; Glen H Crawford, MD, Assistant Clinical Professor, Department of Dermatology, University of Pennsylvania School of Medicine; Chief, Division of Dermatology, The Pennsylvania Hospital; Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center

Author and Editor Disclosure

Synonyms and related keywords: NPDC, nasopalatine canal cyst, incisive canal cyst, nonodontogenic cyst

INTRODUCTION

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Background

The nasopalatine duct cyst (NPDC) is a developmental, nonneoplastic cyst that is considered to be the most common of the nonodontogenic cysts. NPDC 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.

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.1

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.2
 
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.1 In some vertebrates (eg, snakes), the nasopalatine duct plays a role in the reception of odorants.3

The nasopalatine ducts ordinarily undergo progressive degeneration; however, the persistence of epithelial remnants may later become the source of epithelia that gives rise to NPDC, from either spontaneous proliferation1, 4, 5, 6 or proliferation following trauma (eg, removable dentures), bacterial infection, or mucous retention.1, 5, 7, 8 Genetic factors have also been suggested.5, 9 The mucous glands present among the proliferating epithelium can contribute to secondary cyst formation by secreting mucin within the enclosed structure.10 NPDC 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.11

Frequency

United States

Data concerning the prevalence of NPDCs differ considerably, with rates of 0.08%12 to 33%13 having been reported. NPDCs account for approximately 12% of all jaw cyst tumors.14 They occur in both black and white populations.7

Race

No racial predilection is known.

Sex

Males are affected 1.8-20 times more often than females,10, 15, 16 although the predilection for males is not so obvious in all studies.5, 17, 18, 19

Age

NPDCs occur over a wide age range (7-88 y), and they also occur in fetuses.7, 20 Most patients who are affected are aged 30-60 years.4, 21, 22, 23


CLINICAL

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History

  • Small cysts in the early stages of their development are frequently (40-87%) asymptomatic.7, 14, 16, 17, 18, 20
  • 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. About 70% of patients experience a combination of these symptoms. Sometimes, fistula formation or an inability to wear dentures is observed.7, 14
  • Paradoxically, patients with small cysts may have disproportionately severe symptoms, whereas patients with large ones may experience few or no symptoms.17, 24
  • A salty taste in the mouth and devitalization of the pulps of associated teeth have been reported.11, 19, 25

Physical

  • 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.
  • NPDCs 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,17, 24 whereas bony expansion is noted in only 1.4% of patients.17

Causes

The cause of NPDC is essentially unknown. 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.


DIFFERENTIALS

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Other Problems to be Considered

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 NPDC; however, other benign entities that develop within the jawbones with some frequency can mimic NPDC and should be considered in the clinical differential diagnosis.

  • 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)

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


WORKUP

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Imaging Studies

  • Panoramic, occlusal, and periapical radiographs are standard in the radiographic evaluation of suspected NPDC.
  • In some cases, obtaining a 3-dimensional view of the lesion may be necessary.
    • Harris and Brown26 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 al27 reported CT scan characteristics believed to be unique to NPDCs. 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 NPDC.
    • MRIs of NPDCs show homogeneous high-signal intensity on both T1- and T2-weighted images in the area of the contents of NPDCs (keratin and viscous fluids). MRI is more specific than CT.14, 23, 28
  • 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.
    • The mean radiographic diameter is reported to be 17.1 mm.11, 17
    • 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.24
    • In some individuals, a prominent incisive canal can appear as a radiolucent area and mimic NPDC.
    • 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.17

Procedures

  • Aspiration
    • 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 NPDC; 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: 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 71.8% of NPDCs have squamous, columnar, cuboidal, or some combination of these epithelial types; respiratory epithelium is seen in 9.8%.11, 17, 20 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.9 Rarely, dendritic melanocytes have been reported within the epithelium.29 Malignant transformation of the lining epithelium has not been reported.21

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.16 Also helpful in the microscopic diagnosis of NPDC 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).

The cyst fluid has been reported to contain erythrocytes, leukocytes, desquamated epithelial cells, tissue debris, and bacteria.1


TREATMENT

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Surgical Care

NPDCs are treated by enucleation via a palatine or buccal approach.

  • Recurrence is uncommon, having been reported in 0-11% of patients.11, 17, 19
  • If components of the long sphenopalatine nerve are removed during surgery, it may cause paresthesia to the anterior palate.18, 19
  • Complete bone regeneration within the bony defect is expected postoperatively.


FOLLOW-UP

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Complications

Paresthesia to the anterior palate may occur if components of the long sphenopalatine nerve are removed or damaged during surgery.18, 19

Prognosis

Complete postsurgical bony regeneration is expected in most patients. After surgical treatment, recurrence is uncommon, having been reported in 0-11% of patients.11, 17, 19 Only 2 cases of malignant change in the lining epithelium of a NPDC have been published.30, 31


MISCELLANEOUS

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Medical/Legal Pitfalls

Failure to diagnose this type of cyst may result in permanent dental damage.


MULTIMEDIA

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Media file 1:  An ovoid radiolucent area between the central incisor teeth with a poorly defined sclerotic outline can be suspected to be a cyst.
Click to see larger pictureClick to see detailView Full Size Image
Media type:  X-RAY

Media file 2:  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.
Click to see larger pictureClick to see detailView Full Size Image
Media type:  X-RAY

Media file 3:  An ovoid radiolucent area with a poorly defined sclerotic outline between the central incisor teeth.
Click to see larger pictureClick to see detailView Full Size Image
Media type:  X-RAY


REFERENCES

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Nasopalatine Duct Cyst excerpt

Article Last Updated: Mar 25, 2008