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    Cysts and cystic lesions Cysts and cystic lesions Document Transcript

    • 9 D][:Ir162 Ii[ I PATHOLOGY Cysts and cystic lesions of the jaws P. R. MorganIn this article, some recent findings on benign cysts and cystic neoplasms of odontogenic origin arereviewed with special regard to their diagnostic relevance. Emphasis is given to less common lesionsand those which present diagnostic difficulty or which may involve more complex management.Some recent applied research contributions in this area will also be included.Introduction odontogenic cysts and tumours. Whilst all cysts lined by stratified epithelium contain the primary keratins ofThe jaws are unique in the skeleton in the amount and keratinocytes, 5 and 14, keratocysts express keratins 1variety of epithelial residues contained within them and and 10 (markers of cornification) as well as 4 and 13in the range of cystic lesions to which they give rise. (markers of non-cornified epithelium). Dentigerous andManagement of such lesions is a significant proportion radicular cysts also express keratins 4 and 13. Keratinof the work-load of oral and maxillofacial surgeons 19 is expressed in odontogenic epithelia under all cir-and relies on good pre-operative interpretation of radio- cumstances, normal development, adult vestiges, cystsgraphs and computerised tomography (CT) scans and and neoplasms (Fig. 1). Indeed, its presence is so con-accurate histopathological diagnosis of biopsy and surgi- sistent that it could be considered an obligatory keratincal specimens. To some extent, it is artificial to separate of odontogenic epithelium and has the potential to bethe histopathological features from clinical and radio- of diagnostic value. 5 Keratins 8 and 18, found in abun-logical appearances when considering these lesions, as in dance in simple epithelia, are expressed at low but vari-other, longer reviews in this area 1,2and therefore descrip-tions will not always be confined to histopathology.For the purposes of this account, cysts will be dividedinto benign cysts of odontogenic and non-odontogenicorigin and cystic neoplasms (benign and malignant).Non-epithelial lined cysts will be mentioned briefly.General characteristics of odontogenic epitheliumFrom the range and complexity of normal structures andpathological lesions to which it gives rise, odontogenicepithelium must be regarded as pluripotent? This isborne out by the repertoire of keratin proteins which areexpressed in the developing normal tooth germ4 and in Fig. 1--A frozen section of an odontogenic keratocystP. R. Morgan, BSc, BDS, PhD, MRCPath, Departmentof Oral stained with a monoclonal antibody to demonstrate keratinMedicine & Pathology,UMDS, Floor 28, Guys Tower, Guys 19, present in all odontogenic epithelia. Streptavidin-biotinHospital, London SE1 9RT, UK peroxidase reaction,Current Diagnostic Pathology (1995) 2, 86-939 1995 Pearson Professional Ltd 86
    • CYSTS AND CYSTIC LESIONSOF THE JAWS 87 Table-~Simplified classification of jaw cysts ODONTOGENICCYSTS Developmental Dentigerous cyst Eruption cyst Odontogenic keratocyst Lateral periodontal cyst Botryoid odontogeniccyst Glandular odontogeniccyst Inflammatory Radicular cyst, lateral radicular cyst, residual cyst, paradental cyst NON-ODONTOGENICCYSTS Nasopalatine duct cyst Fissural cyst CYSTIC NEOPLASMS AmeloblastomaFig. 2 - - H y a l i n e bodies in the lining of a radicular cyst. Unicystic ameloblastomaThese structures are probably a secretion product, unique Calcifying odontogeniccystto o d o n t o g e n i c epithelia and similar to enamel cuticle,which may be deposited concentrically on a templatelayer. H&E. completion of tooth development and eruption. A major division into developmental 13 and inflammatory catego-able levels in keratinocytes of odontogenic cysts, apart ries is usual.from keratocysts, and of course in zones of mucousmetaplasia. Dentigerous cyst (follicular cyst) Hyaline bodies (Rushton bodies) are highly eosino-philic, laminated, circular or folded elongate structures This cyst is diagnosed by its precise relationship with the(Fig. 2) which lie in the epithelium of about 10 per cent crown of an unerupted tooth, commonly the lower thirdof all forms of odontogenic cyst but do not occur in other molar or upper permanent canine. Being derived fromcyst types. There is considerable evidence now that they the reduced enamel epithelium, the remnant of therepresent a secretion product, probably similar to dental enamel organ, it is attached to the tooth at the enamel-cuticle which is deposited in variable amounts on tooth cementum junction (Fig. 3A). It is therefore importantenamel at the completion of its formation. The available for diagnosis that the tooth is supplied with the softhistological, histochemical and ultrastructural evidence tissue specimen, or at least that accurate clinical inlor-supports the view that it is a product of odontogenic epi- marion is supplied by the operator. Radiographically,thelium secreted on to a template of endogenous or they are unitocular but the illusion of a dentigcrousexogenous origin e.g. cholesterol crystal, root fragment cyst on a radiograph can be given by other radiolucentor root filling material)When present, hyaline bodies lesions which may secondarily involve or displace anmay therefore be considered a marker of odontogenic unerupted looth, such as an ameloblastoma (see below).cysts. Histologically, the cyst lining is characterised by uniform, non-keratinised epithelium, either stratified squamous about 4 10 cells thick or with a cuboidal basalCyst growth layer, thus often resembling reduced enamel epithelium.There is a considerable literature on possible mecha- Mucous metaplasia is frequently encotmtered (Fig. 3B).nisms of cyst initiation and subsequent enlargement. 7 In the young patient, the wall is myxoid and containsTheories have ranged from the osmotic/hydrostatic clusters of odontogenic epithelial rests and in morepressure concept of Toiler s to differential growth 9 and mature follicles these often show cementicle-like miner-inflammatory mediators such as prostaglandins m and, alisation. The immature, myxoid follicle has been vari-more recently, interleukins. ~ There is little doubt that ously misdiagnosed as odontogenic cyst, myxoma,fluid-filled cysts are under positive hydrostatic pressure odontogenic fibroma, odontome and even ameloblas-but it may be doubtful whether this is transmitted as toma.~4 Rests of odontogenic epithelium in the wall maya resorptive force to the surrounding bone, especially also form squamous pearls such as are found in greateras the cell population of most cyst walls includes profusion in the squamous odontogenic tumour. In suchmyofibroblasts which may serve to contain the pressure pearls basal cells are inconspicuous and mitoses exceed-generated. ~2 ingly rare. It is not always possible to establish the point A simple classification of jaw cysts 1,2 groups them at which an enlarged follicle becomes a dentigerousbroadly according to pathogenesis, with odontogenic cyst. Although there is rarely unanimity, a practicalcysts making up the largest proportion (Table). guide to the diagnosis of a cyst is a follicular space of 5 mm or more on a radiograph and a lining of stratified squamous epithelium as well as, or instead of, reducedOdontogenic cysts enamel epithelium.These are derived from residues of odontogenic epithe- As developmental jaw cysts are usually symptomless,lium which otherwise gradually involute following secondary inflammatory changes often provoke initial
    • 88 CURRENTDIAGNOSTICPATHOLOGY(A) (A)(B) (B)Fig. 3--A dentigerous cyst on a lower third molar tooth. (A) Fig. 4--Part of an odontogenic keratocyst which has formedThe cyst wall, attached at the enamel-cementum junction, alongside an unerupted tooth. (A) The white, folded lininghas been partially removed after fixation to reveal the reveals the presence of keratinising epithelium. Proximitycrown of the tooth. (B) Part of the vascular fibrous wall of a to a tooth is an incidental but not uncommon feature anddentigerous cyst lined by non-keratinised stratified on a radiograph may simulate a dentigerous relationship.squamous epithelium which shows a zone of mucous (B) Characteristic histological appearance of anmetaplasia. Such an appearance is characteristic in the odontogenic keratocyst epithelium: uniform thickness andabsence of inflammation. H&E. with a flat basal surface, elongate basal cells, a thin prickle cell zone and corrugated parakeratin surface layer. The fibrous wall is usually thin, delicate and vascular. H&E.presentation and a high proportion of surgical specimensof dentigerous cysts show lymphoplasmacytic infiltrates folded inner surface (Fig. 4A) following discharge ofin the wall and neutrophils in the epithelial lining. Accu- stacked keratin, as with an epidermoid cyst. In mostmulations of cholesterol clefts, foreign body giant cells cases, there should be little difficulty in establishing theand haemosiderin-laden macrophages may greatly en- diagnosis histologically. Typically, the wall is thin andlarge the wall and locally herniate into the cyst lumen. rarely removed intact. It is lined by uniform, para-Thus, at cut-up, disrupted cysts may glisten with keratinised epithelium, some 10-12 cells thick, with adischarging semi-fluid contents which are rich in flat basal surface (Fig. 4B). Key features are a narrow,cholesterol. folded (corrugated) zone of keratin, prickle cells which retain their long axes at right angles to the basement membrane until close to the keratinised layer and elon-Odontogenic keratocyst (primordial cyst) gate, often palisaded, basal cells which show reversedMore has been written in recent years on the polarity in at least some areas. It was established manyodontogenic keratocyst than on any other jaw cyst. years ago that keratocysts show a higher frequencyRadiographically it has a multilocular, or apparently of mitoses than is found in other odontogenic cysts. 15multilocular, appearance and is sometimes multiple, Mitotic figures may be found in both basal and parabasalespecially when it represents a manifestation of the layers. A study using PCNA as a marker of cell prolif-naevoid basal cell carcinoma syndrome (Gorlins syn- eration has shown higher indices for keratocysts than fordrome). Rather than expanding the jaw, the cyst tends other odontogenic cysts. 16 Odontogenic keratocysts haveto grow mesiodistally at the expense of the medullary a higher recurrence rate too, due in part to their physicalbone and extends between the roots of the teeth. fragility leading to disruption during removal, the Macroscopically, the opened cyst reveals a white, epithelium separating easily from the fibrous wall. A
    • CYSTS AND CYSTICLESIONSOF THE JAWS 89further possible reason is the presence of daughter cysts diagnosis in such cases, especially if the biopsy samplein the wall which may remain after cyst enucleation. is small. Differences in proliferation rates and in the frequencyof basal epithelial" cell budding between solitary, multi- Lateral periodontal, botryoid, and glandularple and recurrent odontogenic keratocysts and those odontogenic cystsassociated with naevoid basal cell carcinoma syndromehave been the subject of a number of recent studies. 17 The lateral periodontal cyst is usually unilocular and liesSignificantly higher rates of mitosis occur in keratocysts alongside a vital tooth and therefore, like the radicularin patients with Gorlins syndrome. Satellite cysts have cyst, is presumed to originate from cell rests of Malassezbeen detected in about 50% of syndrome patients and in in the periodontal ligament or possibly from part ofthe walls of 25% of multiple or recurrent cysts whereas the developing follicle, z~ The stimulus to its formation isthey are found in less than 10% of solitary keratocysts. unknown, and it is usually detected as a symptomlessIn practical terms, the possible diagnosis of naevoid radiolucency on routine radiography. Its epithelial liningbasal cell carcinoma syndrome should be investigated is about 2-6 cells thick, non-keratinised, stratifiedfor all patients with odontogenic keratocysts. The syn- squamous and with a flat basal surface. There may bedrome is an autosomal dominant condition with numer- a narrow zone of subepithelial hyalinisation, a featureous defects, many involving the axial skeleton. occasionally encountered in other odontogenic cysts and It is important not to diagnose as a keratocyst every neoplasms. The fibrous wall is usually uninflamed,odontogenic cyst which shows some keratinisation. Parts cellular and delicate, lacking daughter cysts. A charac-of (probably) long-standing dentigerous or radicular teristic feature is the presence of periodic, plaqueqikecysts may show ortho- or parakeratinisation but without thickenings in the epithelium (unrelated to inflamma-the other features of odontogenic keratocysts. Also, soft tion) which may bulge into the cyst lumen or wall ortissue removed together with impacted, partially erupted both (Fig. 6). These contain glycogen and may bethird molar teeth may include some keratinised gingival composed predominantly of clear cells but there is nomucosa which may unwittingly be mistaken for kera- evidence that they represent centres of proliferation.tocyst wall. It is of interest that, whilst all odontogenic Indeed, mitotic figures, epithelial budding and daughterkeratocysts keratinise, only a minority are orthokera- cyst formation are unusual in the lateral periodontal cyst.tinised; moreover, these recur less frequently than A proportion of cysts which radiographically suggestparakeratinising cysts. 18,19 a diagnosis of lateral periodontal cyst turn out to be Although inflammatory infiltrates in odontogenic odontogenic keratocysts on histological examination,keratocysts are usually well-localised and mild, diagnos- despite their unilocular profile.tic problems may result from an ~xtensive inflammatory Botryoid and glandular odontogenic cysts are rareinfiltrate which suppresses keratinisation (Fig. 5). This entities with features in common with each other andcould give rise to misdiagnosis of a dentigerous or re- with the lateral periodontal cyst. The former is so calledsidual cyst with the consequence that, in the absence because the low magnification appearance or macro-of follow-up, the patient may develop a recurrence scopic cut surface sometimes resembles a bunch ofwhich is unrecognised until well advanced. If, in a simi- grapes. Radiographically, most have been multilocularlar context, the basal cells are markedly columnar the and located in the mandible. In their more detailed fea-keratocyst might be misdiagnosed as an ameloblastoma, tures, botryoid cysts resemble lateral periodontal cysts,particularly since the radiographic appearance of these the thin, non-keratinised epithelial lining with thickenedtwo lesions are sinfilar. One should be wary of over- plaques being a consistent feature. A number of recent 4~Fig. 5 - - A keratocyst which has become secondarily Fig, 6--Wall of a lateral periodontal cyst with a Iocalisedinflamed. Note the loss of keratinisation in the zone thickening of the uniform, non-keratinising epithelium.showing an arcading pattern of epithelial hyperplasia. If the Several such thickenings may be encountered in a givenbiopsy is small or inflammatory change extensive, this may plane of section. H&E.lead to a mistaken diagnosis of an inflammatory cyst. H&E.
    • 90 CURRENTDIAGNOSTICPATHOLOGYpublications point to a high recurrence rate for thismulticystic lesion. Greater difficulty attaches to the status of the glandular(sialo- or mucoepidermoid-) odontogenic cyst. It is sur-prising that this cyst has been recognised only recentlyas a distinct entity 21,22 and less than 20 cases have beenreported in the world literature. It has an appearance ofmultilocularity on radiographic examination. Its histo-logical features include multiple thickened epithelialplaques, like those of the lateral periodontal cyst, andmulticystic growth, like the botryoid cyst. Intriguingadditional features are present in the epithelium: papil-lary outgrowths into the cyst lumen with apocrine-likedecapitation secretion of surface cells, ductal struc- Fig. 8--Radicular cyst: a frequent presentation with atures, mucin-producing goblet cells and occasionally dense, mixed inflammatory infiltrate adjacent to variablyacini (Fig. 7). The nomenclature for this cyst has not yet hyperplastic, non-keratinised epithelim. The upper part of the field shows part of the wall apparently devoid ofbeen established and interpretations of the histological epithelium, also a common finding. H&E.features range widely. Mucous metaplasia may bepresent in the lining of any odontogenic cyst and to somecommentators, the glandular odontogenic cyst is an ex- pattern of hyperplasia (Fig. 5) can be so striking that thetreme example of this change. An opposing view is that unwary may suspect the presence of an ameloblastoma. 23the lesion is in fact a low-grade central mucoepidermoid It is essential that the condition of the related tooth becarcinoma. When more cases become available for study known for the correct diagnosis to be made: the histo-and when a wider range of markers of odontogenic logical features of a radicular cyst may be identicalepithelium have been developed, the histogenesis of this to those of a secondarily inflamed dentigerous cyst.group of cysts should become clearer. Similarly, a long-standing radicular cyst may come to resemble a developmental cyst when the inflammatoryInflammatory odontogenic cysts infiltrate fades. A cyst which forms alongside a non-vital tooth is termed a lateral radicular cyst and one which isRadicular cyst retained following removal of the offending tooth or rootBy far the most common jaw cyst is the radicular cyst, is referred to as a residual cyst, the histological featuresan odontogenic cyst which forms from epithelial rests of being identical to those just described.Malassez in the periodontal ligament consequent uponactivation from the products of necrotic dental pulp in an Paradental cystadjacent tooth. The wall is relatively thick and usuallycontains a dense inflammatory infiltrate towards the The paradental cyst is an inflammatory cyst which liesinner aspect, consisting of plasma cells and lymphocytes. on the disto-buccal aspect of fully or partially eruptedNeutrophils tend to accumulate in the epithelium which third molar teeth, near the bifurcation of the rootsis of non-keratinised, stratified squamous type and varies (Fig. 9). There is a male preponderance, a history ofgreatly in thickness (Fig. 8). Sometimes the arcading pericoronitis is common and sometimes a predisposingFig. 7--Parts of two Iocules of a glandular (sialo-) Fig. 9--A paradental cyst attached to the enamel-cementumodontogenic cyst with thickened epithelial plaques, similar junction of a lower molar tooth on the disto-buccal aspect.to those found in lateral periodontal and botryoid cysts but Although slightly disrupted, it lies alongside the tooth andalso showing ductal structure, and extensive mucus- does not enclose the crown.secreting cells. H&E.
    • CYSTS AND CYSTICLESIONSOF THE JAWS 91factor is an extension of enamel down to where the roots Differential diagnosis should include other odonto-separate and a bilateral presentation is not u n u s u a l . 24 The genic carcinomas: primary intra-osseous carcinomas,associated tooth is therefore usually vital and such cysts which are thought to arise from residues of odontogenicare often removed still attached after extraction of the epithelium in the jaws, and malignant variants oferupting or partially erupted tooth due to impaction. ameloblastoma and other odontogenic tumours. CentralWhether the source of epithelium is the reduced enamel mucoepidermoid carcinomas, in which the epidermoidepithelium, periodontal pocket epithelium or cell rests component may predominate, should also be considered.of Malassez, the aetiological mechanism appears to be Any of these malignancies may be cystic, at least inepithelial activation by inflammatory infiltrate which is part. The mandible is also a well-recognised site for car-induced by bacterial plaque. cinomas metastatic to the jaws from such sites as lung, A related cyst, the mandibular infected buccal cyst, breast, prostate, thyroid and kidney which may simulatehas a similar association with first or second lower per- cysts radiographically.manent molar teeth 25 but in younger patients than the Dysplastic change may be encountered in cyst epithe-paradental cyst. As Shear 2 argues, the two entities are lia and levels should be checked carefully for evidenceprobably related but are worth while recognising as of frank invasion. This is particularly the case in thosedistinct for reasons of management. odontogenic keratocysts which show basal budding Both these cysts have the same histological appear- (Fig. 11) and epithelial islands, since the presence ofance as the radicular cyst: hyperplastic, non-cornified dysplasia may give the impression of a wide field ofepithelium lining a fibrous wall containing a dense, invasion.mixed inflammatory infiltrate. Clinical information istherefore essential for an accurate diagnosis. AmelobIastoma and its unicystic variants Ameloblastomas are the most common odontogenic neo-Malignant transformation in jaw cysts plasms. They present usually in the mandibular thirdAlthough rare, malignant transformation does occur in molar region and least often in the anterior maxilla.odontogenic cysts, about 60 cases having been reported Their peak age prevalence is in the 4th or 5th decade.in the world literature. Malignant transformation appears Histological criteria for their diagnosis were set out byto arise most frequently in residual cysts, reported cases Vickers and Gorlin. 27 The epithelial cells comprise twoequalling those of dentigerous cysts and odontogenic distinct populations. Firstly, peripheral, or basal, cellskeratocysts combined; 80% of such malignancies occur which are columnar and often markedly elongate andin the mandible (Fig. l()). 2r Not surprisingly, the age at showing reversed polarity, with the nucleus occupyingpresentation tends to be greater than that of patients with the part of the cell away fi-om the basement membrane;benign cysts; the 6th or 7th decade rather than the 4th or this layer thus resembles the pre-ametoblast of the devel-5th. As far as can be assessed with such small numbers oping tooth germ. The second population consists ofof cases, the prognosis appears to be better than that of polyhedral suprabasal cells with fewer intercellular con-mucosal carcinomas which infiltrate the .jaws, and that tacts than conventional prickle cells; this is the stellateof primary intra-osseous carcinomas, nodal metastases reticulum-like layer, similar to the stellate reticulum ofbeing less common. This difference in prognosis might the bell stage in the developing tooth. Two principalbe expected when the carcinoma is removed while being arrangements of epithelium are recognised, follicularretained within the confines of the fibrous cyst wall. (Fig. 12A) and plexiform (Fig. 12B), although there isFig. 10--Squamous cell carcinoma which has arisen in an Fig. 11--Odotogenic keratocyst showing extensive basalodontogenic keratocyst. This mandibular t u m o u r was more budding together with bulbous rete processes and somesolid than cystic but dysplastic keratocyst lining is still cell disorganisation but minimal cytological features ofevident associated with islands of well-differentiated malignancy. However, the presence of these featurescarcinoma. A dense lymphocytic response is also present. increase the likelihood of recurrence. H&E.H&E.
    • 92 CURRENTDIAGNOSTICPATHOLOGY be confused with an odontogenic keratocyst. 28 An addi- tional but rare feature of ameloblastomas is the inclusion of eosinophilic granular cells whose origin is obscure but which are befieved to arise in the epithelial compartment. Other variants of ameloblastoma may also be pre- dominantly cystic: 9 Desmoplastic, in which the stroma is more densely fibrous. 9 Basal cell, in which basaloid cells predominate. 9 Papilliferous keratoameloblastoma, a rare type in which cystic spaces may be filled with desquamated, kerati- nising squames. Some ameloblastomas are characteristically unilocular(A) on radiographs and prove to be unicystic (Fig. 13), and sometimes in a dentigerous relation to a tooth, when examined macroscopically. They also tend to present in younger patients than do conventional ameloblastomas. Levels should be taken through the excision specimen to investigate the presence of a conventional amelo- blastoma. Sometimes part of the lining expands into a plexiform pattern of ameloblastoma. On occasion, strict criteria for ameloblastoma can be hard to establish and the diagnosis has to take account of the clinical presenta- tion as well as suggestive features in the epithelial lin- ing. Unicystic ameloblastomas are generally considered to have a lower recurrence rate than their conventional counterparts. This is true of those with a continuous epithelial lining and those with ameloblastomatous mural(B) nodules which invaginate the lumen. They may beFig. 12--Examples of cyst formation in conventional treated successfully by careful enucleation, but whenameloblastomas. (A) Follicular ameloblastomas with cystic the wall is found to be infiltrated by islands of amelo-change in the stellate reticulum component of theneoplasm. The cystic area on the right is lined by cells blastomatous epithelium treatment should be as radicalshowing acanthomatous change. (B) Plexiform as for the conventional solid or multi-cystic types. 13ameloblastomas with stromal cysts; surviving small bloodvessels indicate the location of the connective tissuecomponent. The lumen of the main cyst is shown at the topof the figure and is composed of degenerate epithelial cells. Calcifying odontogenic cystH&E. This curious entity is usually classified with epithelial odontogenic tumours since it is really a neoplasm which sometimes may be as aggressive as an ameloblastoma.no behavioural difference between the two. Althoughusually slow growing and lacking in detectable mitoses,both types tend to infiltrate the bone and to recur unlessremoved by local resection. The follicular form consistsof round or irregular islands of tumour, the stroma beingcomposed of vascular, cellular fibrous tissue. As its de-scriptive name suggests, in the plexiform ameloblastomathe epithelial component takes the form of interlacingstrands which appear to entrap the stroma. Cystic changeis common in both types, microcysts forming in theepithelial masses and stromal cysts in the connectivetissue. As the ameloblastoma enlarges, the cysts coalesceand may form one or more cystic cavities containingstraw-coloured fluid. Biopsy of the stretched wall ofsuch a tumour may lead to the misdiagnosis of a non-neoplastic cyst. Fortunately, the solid or invaginated Fig. 13--Unicystic ameloblastoma. This lesion shows fewareas are likely to contain more representative amelo- histological hallmarks of an ameloblastoma, Basalblastoma. Another conmaon feature of ameloblastomas is epithelial cells palisaded in places but with little evidence of the reversed polarity characteristic of ameloblasts andsquamous metaplasia (acanthomatous change) which stellate reticulum cells are poorly developed. Epithelium inonly rarely consists of true keratinisation when it may this field has a somewhat plexiform arrangement. H&E.
    • CYSTS AND CYSTIC LESIONS OF THE JAWS 93 Browne R, ed. Investigative pathology of odontogenic cysts. CRC Press, 1991:53 85. 4. Heikinheimo K, Sandberg M, Happonen R-P, Virtanen I, Bosch F. Cytoskeletal gene expression in normal and neoplastic human odontogenic epithelia. Lab Invest 1991; 65: 688-701. 5. Morgan P R, Shirlaw P J, Johnson N W, Leigh I M, Lane E B. Potential applications of anti-keratin antibodies in oral diagnosis. J Oral Pathol 1987; 16: 212-222. 6. Morgan P, Johnson N. Histological, histochemical and ultrastructural studies on the nature of hyalin bodies in odontogenic cysts. J Oral Pathol 1974; 3: 127-147. 7. Browne R, Smith A. Pathogenesis of odontogenic cysts. In: Browne R, ed. Investigative pathology of odontogenic cysts. CRC Press, 1991: 87-109. 8. Toiler P. The osinolality of fluids from cysts of the jaws. Brit Dent J 1970; 129: 275-278. 9. Kramer I R H. Changing views on oral disease. Proc Roy Soc Med 1974; 67: 271-276.Fig. 14--Calcifying odontogenic cyst with characteristic 10. Harris M, Toller P. The pathogenesis of dental cysts. Brit Medghost cells suprabasally. Basal and parabasal layers Bull 1975; 31: 159-163.resemble eqivalent cells in ameloblastomas. Groups of 11. Meghji S, Henderson B, Bando Y, Harris M. Interleukin-1: theghost cells may find their way into the connective tissue principal osteolytic cytokine produced by keratocysts. Archs oraland stimulate a foreign body reaction. H&E. Biol 1992; 37: 935-943. 12. Lombardi T, Morgan P R. hnmunohistochemical characterisation of odontogenic cysts with mesenchymal and myofilament markers. J Oral Pathoi Med 1995; 24:170 176. 13. Shear M. Developmental odontogenic cysts. An update. J OralIt s h o w s a w i d e site and age variation 29 but is c o n f i n e d PatholMed 1994; 23:1 11.to the t o o t h - b e a r i n g r e g i o n s o f the j a w s . S o m e t i m e s the 14. Kim J, Ellis G. Dental follicular tissue: misinterpretation asc a l c i f y i n g o d o n t o g e n i c cyst is not cystic and often it odontogenic tumors. J Oral Maxillofacial Surg 1993; 51: 762-767. 15. Browne R. The odontogenic keratocyst histological features andd o e s not calcify. Its basal cells and parabasal epithelial their correlation with clinical behaviour. Br Dent J 197 I;cells r e s e m b l e t h o s e o f the a m e l o b l a s t o m a but m o r e 131 : 249-259.superficial cells e x p a n d to f o r m lightly e o s i n o p h i l i c , 16. Li T-J, Browne R, Matthews J. Quantification of PCNA+ ceils within odontogenic jaw cyst epithelium. J Oral Pathol Med 1994;partially keratinising and usually n u c l e a t e cells t e r m e d 23:184 189. g h o s t c e l l s (Fig. 14). T h e s e may b e c o m e c a l c i f i e d and 17. Woolgar J A, Rippin J W, Browne R M. A comparativeare not d i s s i m i l a r to cells o f the p i l o m a t r i x o m a wilh histological study of odontogcnic keratocysts in basal cell naevus syndrome and control patients. J Oral Pathol 1987; 16: 75-80.w h i c h this lesion has often been c o m p a r e d . G h o s t cells 18. Brannon R. The odontogcnic keratocyst. A clinicopathologic studyare not u n i q u e to the c a l c i f y i n g o d o n l o g e n i c cysl but {71312 cases. Part 11. Histoh}gical features. Oral Surg Oral Medhave been d e s c r i b e d in cases o f a m e l o b l a s t o m a , a m e l o - Oral Pathol 1977: 43:233 255. 19. Wright J. The odontogenic kcratocyst: orthokcratinizcd w,iant.Mastic fibroma and ameloblastic fibroodonlome. A Oral Surg Oral McdOral Pathol 1981; 51: 609 618.further feature seen in a proportion o f cases is the d e p o - 20. Allini M, Shear M. The lateral periodontal cyst: an update. J Oralsition of poorly mineralised dysplastic dentine or Pathol Med 1992; 21:245 250. 21. Padayachee A, Van Wyk C W. Two cystic lesions with features ofdentinoid" in the cyst wall. S o m e t i m e s typical dental both the botyroid odontogeuic cyst and lhc centralhard tissues f o r m , in w h i c h case one has to c o n s i d e r mucoepidcrmoid turnout: sialo odontogenic cyst? J Oral Patholw h e t h e r o d o n t o m e s h o u l d be the m o r e a p p r o p r i a t e 1987; 16: 499-504. 22. Gardner D G, Kessler H P, Morency R, Schaffner D L. Thed e s i g n a t i o n , a d e c i s i o n for w h i c h the age, site and radio- glandular odontogenic cyst: an apparent entity. J Oral Patholgraphic a p p e a r a n c e should be taken into account. As 1988; 17:359 366.t h e s e turnouts are rather rare, this material has scarcely 23. Lucas R. Pathology of Tumours of the Oral Tissues. 4th ed. Edinburgh: Churchill Livingstone, 1984.b e e n tested for its authenticity as dentine. A d i a g n o s i s 24. Craig G. The puradental cyst. A specific inflamnmtoryo f c a l c i f y i n g o d o n t o g e n i c cyst is not a clear p o i n t e r to a odontogenic cyst. Br Dent J 1976; 141:9 14.l e s i o n s likely behaviour. D e t a i l e d a n a l y s i s o f 92 c a s e s 25. Stoneman D, Worth H. The mandibular bucca] infected cyst - molar area. Deut Radiol Photog 1983; 56:1 14.e m p h a s i s e d the n e e d to s u b g r o u p t h e m into h a m a r t o - 26. Schwimmer A, Aydin F, Morrison S. Squamous ceil carcinomamatous, cystic and n e o p l a s t i c variants. 29 arising in residual odontogenic cyst. Oral Surg Oral Med Oral Pathol 1991; 72: 218--221. 27. Vickers R, Gorlin R. Ameloblastoma: delineation of earlyReferences histopathologic features of neoplasia. Cancer 1970; 26:699 710. 28. Siar C, Ng K. Combined ameloblastoma and odontogenic 1. Kramer 1, Pindborg J, Shear M. Histological typing of keratocyst or keratinising ameloblastoma. Br J Oral Maxfac odontogenic tumours 2nd ed. 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