Pathology of the Head and Neck

108 P.J. Slootweg4Fig. 4.9. Epithelial lining of a keratocyst. The basal palisadingand the corrugated parakeratinised surface are unique to this lesion.Moreover, there is a striking parallel between the basal layerand the surfaceFig. 4.10. In the event of inflammation, the epithelial lining of akeratocyst loses its typical pattern to transform into a lattice ofspongiotic squamous epitheliumThe odontogenic keratocyst shows a thin connectivetissue wall lined by stratified squamous epitheliumwith a well-defined basal layer of palisading columnaror cuboidal cells and with a surface of a corrugatedlayer of parakeratin (Fig. 4.9). Mitotic figurescan be identified in parabasilar and midspinous areas[12]. Rushton bodies similar to those seen in radicularcysts may also be present. The underlying cyst wallmay contain tiny daughter cysts and solid epithelialnests. Also, epithelial proliferations similar to ameloblastomahave been reported. Daughter cysts and intramuralepithelial nests are more common in cystsassociated with the nevoid basal cell carcinoma syndrome[185]. When inflamed, the odontogenic keratocystloses its typical histologic features, but showsa non-keratinising stratified epithelium exhibitingspongiosis and elongated rete pegs supported by a connectivetissue containing a mixed inflammatory infiltrate(Fig. 4.10). Rarely, odontogenic keratocysts showdevelopment of epithelial dysplasia and squamous cellcarcinoma [87].Immunohistochemical studies have not yielded dataof diagnostic or prognostic significance [148, 149].Odontogenic keratocysts may also contain mucouscells, melanin-producing cells, dentinoid and intramuralcartilage [12, 74, 86, 105]. Ciliated cells may be seen,but in maxillary cases, they could also be the result of acommunication with the maxillary sinus [122]. In addition,the cyst wall may contain intramural odontogenicepithelial remnants. Occasionally, intraosseous cysts arelined by orthokeratinised epithelium, thus having theappearance of an epidermoid cyst. Such cysts are knownas orthokeratinised odontogenic cysts. Their differentiationfrom the odontogenic keratocyst with parakeratinisationis clinically important as recurrence of orthokeratinisedcysts is rare [188]. Differential diagnosiswith unicystic ameloblastoma (see Sect. 4.4.1.1) maybe difficult. Odontogenic keratocyst exhibits a compactspinous layer and a corrugated superficial parakeratinlayer, and ameloblastoma a spinous layer with intercellularoedema.Keratocysts do not cause symptoms unless concomitantinflammation causes pain and swelling. Radiographsmay reveal extensive uni- or multilocular radiolucentlesions that occupy the major part of the jawwithout having caused any appreciable cortical expansion.When the odontogenic keratocyst forms part ofthe nevoid basal cell carcinoma syndrome, patientsmay show any of the other features of this syndrome[72].Odontogenic keratocysts tend to recur after enucleation[147, 148, 149]. Sometimes, a partial jaw resectionis needed to a provide permanent cure [182]. If associatedwith the nevoid basal cell carcinoma syndrome, thechance of recurrence is even higher [18]. If located in thegingiva, the behaviour of the odontogenic keratocyst isless aggressive [65].As there is sufficient evidence that this lesion actuallyrepresents a cystic neoplasm, the most recent WHOclassification proposes the diagnostic designation keratocysticodontogenic tumour [181].4.3.2.5 Gingival CystGingival cysts are divided in those occurring in adultsand those in infants. They are located in the gingival tissues.Gingival cysts of adults are rarely larger than 1 cmand may be multiple. They are lined by either thin epitheliumof one to three cell layers or thicker and exhibitkeratinisation. Plaques similar to those occurring in thelateral periodontal cyst (see Sect. 4.3.2.2) may be seen[107].