Section 6 -

Cysts and Cyst-like Tumors of the Jaws Pieter J. Slootweg Radboud University Medical Center Nijmegen, The Netherlands

Introduction The jaws contain a variety of neoplastic and non-neoplastic cystic lesions. Generally, they are classified as shown in the Table. Table. Cystic lesions of the jaws A. Odontogenic cysts - inflammatory Radicular cyst Residual cyst Paradental cyst B. Odontogenic cysts - developmental Dentigerous cyst Lateral periodontal cyst Botryoid odontogenic cyst Glandular odontogenic cyst C. Non - odontogenic cysts Nasopalatine duct cyst Nasolabial cyst Surgical ciliated cyst D. Cystic odontogenic tumours Ameloblastoma (unicystic) Keratocystic odontogenic tumour (keratocyst) Calcifying cystic odontogenic tumour Adenomatoid odontogenic tumour E. Pseudocysts, either neoplastic or non-neoplastic Focal bone marrow defect Solitary bone cyst Aneurysmal bone cyst Ossifying fibroma (juvenile psammomatoid) Radicular cysts are located at the root tips of teeth. They arise from the epithelial rests of Malassez and are the cysts most frequently seen. They are lined by nonkeratinizing squamous epithelium that may be thin and atrophic or show elongated rete processes. Within the cyst epithelium, hyaline bodies of various size and shape may be present, the so-called Rushton bodies. Occasionally, the lining squamous cells are admixed with mucous cells or ciliated cells. Sometimes, the histologic pattern of the radicular cyst is complicated by extensive intramural proliferation of squamous epithelial nests of varying size, thus mimicking a squamous odontogenic tumour. When a radicular cyst is retained in the jaws after removal of the associated tooth, the lesion is called residual cyst . The paradental cyst is located at the lateral side of the tooth at the border between enamel and root cementum. This cyst is secondary to an inflammatory process in the adjacent periodontal tissues that induces proliferation of neighbouring odontogenic epithelial rests, similar to the pathogenesis of the radicular cyst. A dentigerous cyst surrounds the crown of an unerupted tooth, mostly the maxillary canine or the mandibular third molar tooth. The cyst wall has a thin epithelial lining that may be only two to three cells thick. In case of inflammation, the epithelium becomes thicker and will show features similar to the lining of a radicular cyst. Also, mucous producing cells as well as ciliated cells may be observed. The cyst wall may also contain varying amounts of epithelial nests representing remnants of the dental lamina. Lateral periodontal cysts are derived from odontogenic epithelial remnants, and occuring adjacent to the roots of vital teeth. They are lined by a thin, non-keratinizing squamous or cuboidal epithelium with focal, plaque-like thickenings that consist of clear cells that may contain glycogen. The botryoid odontogenic cyst represents a multilocular form of the lateral periodontal cyst. The glandular odontogenic cyst is characterized by an epithelial lining with cuboidal or columnar cells both at the surface and lining crypts or cyst-like spaces within the thickness of the epithelium. The lining epithelium is partly nonkeratinizing squamous with focal thickenings similar to the plaques in the lateral periodontal cyst and the botryoid odontogenic cyst. There may be a surface layer of eosinophilic cuboidal or columnar cells that can have cilia and may form papillary projections. Some superficial cells show apocrine features. Also, mucus producing cells may be present. In areas of thickened epithelium glandular spaces are formed. Moreover, the epithelial cells may form whorls. Nasopalatine duct cysts arise within the nasopalatine canal from epithelial remnants of the nasopalatine duct. Radiologically, they present as radiolucent lesions situated between the roots of both maxillary central incisor teeth. The cyst lining may be pseudostratified columnar ciliated epithelium, stratified squamous epithelium, columnar or cuboidal epithelium and combinations of these. As surgical treatment comprises emptying the nasopalatine canal, the specimen always includes the artery and nerve that run in this anatomic structure. These are seen within the fibrous cyst wall and form the most convincing diagnostic feature as the specific epithelial structures may be obscured by inflammatory changes. Nasolabial cysts are located in the soft tissue just lateral to the nose at the buccal aspect of the maxillary alveolar process and are thought to arise from the nasolacrimal duct. Non-ciliated pseudostratified columnar epithelium with interspersed mucous cells form the epithelial lining. These features may be lost through squamous metaplasia. Surgical ciliated cysts arise from detached portions of the mucosa that line the maxillary antrum that are buried within the maxillary bone. The cyst lining consists of pseudostratified ciliated columnar epithelium with interspersed mucous cells. The solitary bone cyst, also known as traumatic bone cyst or simple bone cyst is confined to the mandibular body. It consists merely of a fluid-filled cavity from which material for histologic examination may be difficult to obtain as a soft tissue lining of the bony cavity may be entirely absent or very thin. If present, it usually consists only of loose fibrovascular tissue, although it may also contain granulation tissue with signs of previous haemorrhage such as cholesterol clefts and macrophages loaden with iron pigment. The focal bone marrow defect represents an asymptomatic radiolucent lesion of the jaws which contains normal hematopoietic and fatty bone marrow. It is also called osteoporotic bone marrow defect. Mostly, this condition is seen at the angle of the mandible where it reveals its presence as a radiolucency with more or less well-defined borders. Unicystic ameloblastoma represents a cyst that is lined by ameloblastomatous epithelium. This epithelium may proliferate to form intraluminal nodules with the architecture of plexiform ameloblastoma. Downward proliferation of this epithelium may lead to infiltration of the fibrous cyst wall by ameloblastoma nests. Sometimes, the cyst lining itself lacks any features indicative of ameloblastoma, these being confined to intramural epithelial nests. Inflammatory alterations may obscure the specific histologic details. Adenomatoid odontogenic tumour consists of two different cell populations: spindle shaped and columnar. The spindle shaped cells form whorled nodules that may contain droplets of eosinophilic material. Thin epithelial strands may connect these nodules to each other. The columnar cells line duct-like spaces with a lumen either empty or containing eosinophilic material and may form curvilinear opposing rows with interposed eosinophilic material. In the stroma, there are large aggregates of eosinophilic hyaline material. In some adenomatoid odontogenic tumours, areas of eosinophilic cells with well-defined cell boundaries and prominent intercellular bridges similar to those observed in the calcifying epithelial odontogenic tumour are seen. They do not influence the biologic behaviour of this tumour and are considered to be part of its histologic spectrum. Calcifying odontogenic cyst shows an epithelial lining similar to unicystic ameloblastoma but in addition, there are intraepithelial eosinophilic ghost cells that may undergo calcification. Ghost cell aggregates also may herniate through the basal lamina into the underlying stroma where they evoke a giant cell reaction. In the fibrous stroma adjacent to the basal epithelial cells, homogenous eosinophilic material resembling dentin may be found in varying amounts. Dentin-like material and ghost cells together may lie intermingled. To this simple unicystic structure other features may be added thus creating different subtypes with different names. The most recent WHO classification proposes the diagnostic designations calcifying cystic odontogenic tumour and dentinogenic ghost cell tumour to discern between the cystic and the solid lesion. Keratocystic odontogenic tumour (Odontogenic keratocyst) shows a thin connective tissue wall lined by stratified squamous epithelium with a well defined basal layer of palissading columnar or cuboidal cells and with a surface of a corrugated layer of parakeratin. The underlying cyst wall may contain tiny daughter cysts and solid epithelial nests. When inflamed, the typical histologic features are replaced by a non-keratinizing stratified epithelium exhibiting spongiosis and elongated rete pegs supported by a connective tissue containing an mixed inflammatory infiltrate. They also occur as part of the nevoid basal cell carcinoma syndrome or Marfan's syndrome. Occasionally, intraosseous cysts are lined by orthokeratinized epithelium, thus having the appearance of an epidermoid cyst. Such cysts are known as orthokeratinized odontogenic cyst. Their differentiation from the keratocystic odontogenic tumour is clinically important as recurrence of the orthokeratinized cysts is rare in contrast with the keratocystic odontogenic tumour. Juvenile psammomatoid ossifying fibroma may be largely cystic in its gross appearance. This subtype of ossifying fibroma has a fibroblastic stroma with small ossicles resembling psammoma bodies, hence its name. The stroma varies in cellularity. The spherical or curved ossicles are acellular or include sparsely distributed cells and may coalesce to form trabeculae. Some cases contain basophilic concentrically lamellated particles as well as irregular thread-like or thorn-like calcified strands in a hyalinized background. Trabeculae of woven bone as well as lamellar bone, pseudocystic stromal degeneration and haemorrhages resulting in areas similar to an aneurysmal bone cyst, multinucleate giant cells, and mitotic figures can also be observed. References: Brannon RB. The odontogenic keratocyst. A clinicopathologic study of 312 cases. Part I. Clinical features. Oral Surg Oral Med Oral Pathol 1976, 42:54-72 Gurol M. Burkes EJ, Jacoway J. Botryoid odontogenic cyst: analysis of 33 cases. J Periodontol 1995, 66:1069-1073 Magnusson B, Borrman H. The paradental cyst: a clinicopathologic study of 26 cases. Swed Dent J 1995, 19:1-7 Morgan PR, Johnson NW. Histological, histochemical and ultrastructural studies on the nature of hyaline bodies in odontogenic cysts. J Oral Pathol 1974, 3:127-147 Philipsen HP, Reichart PA. Unicystic ameloblastoma. A review of 193 cases from the literature. Oral Oncol 1998, 34:317-325 Saito Y, Hoshina Y, Nagamine T, Nakajima T, Suzuki M, Hayashi T. Simple bone cyst. 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