Clinical Features

This cyst is always associated initially with the crown of an impacted, embedded or unerupted tooth (Fig. 4-1). A dentigerous cyst may also be found enclosing a complex compound odontoma or involving a supernumerary tooth. The most common sites of this cyst are the mandibular and maxillary third molar and maxillary cuspid areas, since these are the most commonly impacted teeth. Most lesions present in second and third decades, with slight male predilection (M:F–3:2). Most dentigerous cysts are solitary. Bilateral and multiple cysts are usually found in association with a number of syndromes including cleidocranial dysplasia and Maroteaux–Lamy syndrome. In the absence of these syndromes, bilateral dentigerous cysts are rare. The dentigerous cyst is potentially capable of becoming an aggressive lesion. Expansion of bone with subsequent facial asymmetry, extreme displacement of teeth, severe root resorption of adjacent teeth and pain are all possible sequelae brought about by continued enlargement of the cyst. Cystic involvement of an unerupted mandibular third molar may result in a ‘hollowing-out’ of the entire ramus extending up to the coronoid process and condyle as well as in expansion of the cortical plate due to the pressure exerted by the lesion. Associated with this reaction may be displacement of the third molar to such an extent that it sometimes comes to lie compressed against the inferior border of the mandible. In the case of a cyst associated with a maxillary cuspid, expansion of the anterior maxilla often occurs and may superficially resemble an acute sinusitis or cellulitis. There is usually no pain or discomfort associated with the cyst unless it becomes secondarily infected.

Radiographic Features

Radiographic examination of the jaw involved by a dentigerous cyst will reveal a radiolucent area associated in some fashion with an unerupted tooth crown (Fig. 4-2A). The impacted or otherwise unerupted tooth crown may be surrounded symmetrically by this radiolucency, although the distinction between a small dentigerous cyst and an enlarged dental follicle or follicular space is quite arbitrary, especially since the small cyst and the enlarged follicle would be histologically identical. While a normal follicular space is 3–4 mm, a dentigerous cyst can be suspected when the space is more than 5 mm. Only when the size of the radiolucency is grossly pathologic can the distinction be made with assurance.

Three radiological variations of the dentigerous cyst may be observed. In the central variety, the crown is enveloped symmetrically. In these instances, pressure is applied to the crown of the tooth and may push it away from its direction of eruption. In this way, mandibular third molars may be found at the lower border of the mandible or in the ascending ramus and a maxillary canine may be forced into the maxillary sinus as far as the floor of the orbit. The lateral type of dentigerous cyst is a radiographic appearance which results from dilatation of the follicle on one aspect of the crown. This type is commonly seen when an impacted mandibular third molar is partially erupted so that its superior aspect is exposed. The so-called circumferential dentigerous cyst results when the follicle expands in a manner in which the entire tooth appears to be enveloped by cyst. The dentigerous cyst is usually a smooth, unilocular lesion, but occasionally one with a multilocular appearance may occur. In actuality, the various compartments are all united by the continuous cystic membrane. Sometimes the radiolucent area is surrounded by a thin sclerotic line representing bony reaction. In cases of apparently multiple dentigerous cysts, care should be taken to rule out the possible occurrence of the odontogenic keratocyst, basal cell nevus, bifid rib syndrome (q.v.).

Histologic Features

There are no characteristic micro-scopic features which can be used reliably to distinguish the dentigerous cyst from the other types of odontogenic cysts. It is usually composed of a thin connective tissue wall with a thin layer of stratified squamous epithelium lining the lumen (Fig. 4-2B). Rete peg formation is generally absent except in cases that are secondarily infected. The connective tissue wall is frequently quite thickened and composed of a very loose fibrous connective tissue or of a sparsely collagenized myxomatous tissue, each of which has been sometimes mistakenly diagnosed as either an odontogenic fibroma or an odontogenic myxoma. A hyperplastic dental follicle is not necessarily associated with inflammation. An additional feature of the connective tissue wall of both normal dental follicles and dentigerous cysts is the presence of varying numbers of islands of odontogenic epithelium (Fig. 4-2C). These are sometimes very sparse and obviously inactive, while at other times they are present in sufficient numbers to be mistaken for an amelo-blastoma. While this latter odontogenic tumor can originate in this situation, care must be taken to differentiate between it and simply odontogenic epithelial rests. Inflammatory cell infiltration of the connective tissue is common although the cause for this is not always apparent. An additional finding, especially in cysts which exhibit inflammation, is the presence of Rushton bodies within the lining epithelium. These are peculiar linear, often curved, hyaline bodies with variable stainability which are of uncertain origin, questionable nature and unknown significance. Even electron microscopic studies, such as those of El-Labban, have only been of partial help in determining that the structures are probably of hematogenous origin, although it is not clear why they have such an intimate relationship to epithelium. The content of the cyst lumen is usually a thin, watery yellow fluid, occasionally blood tinged.

It was reported by Brannon in his excellent clinicopathologic study of 312 cases of odontogenic keratocysts that 8.5% of a series of 1,850 dentigerous cysts were odontogenic keratocysts (q.v.) with the characteristic histologic findings in the epithelium of a parakeratinized, corrugated surface, a remarkable uniformity of a 6- to 10-cell thickness without rete peg formation, and a polarized and palisaded basal layer of cells. This percentage of dentigerous cysts which are odontogenic keratocysts is in close agreement with the findings of Pindborg and his coworkers (7.1%) and Payne (8.5%).

The pluripotentialities of the epithelium in mandibular dentigerous cysts has been further emphasized by Gorlin, who described mucus-secreting cells in the lining stratified squamous epithelium, respiratory epithelial lining, sebaceous cells in the connective tissue wall, and lymphoid follicles with germinal centers.

Treatment

The treatment of the dentigerous cyst is usually dictated by the size of the lesion. Smaller lesions can be surgically removed in their entirety with little difficulty. The larger cysts which involve serious loss of bone and thin the bone dangerously are often treated by insertion of a surgical drain or marsupialization. Such a procedure is often necessary because of the potential danger of fracturing the jaw if complete surgical removal were attempted. Recurrence is relatively uncommon.

Potential Complications

Several relatively serious potential complications exist stemming from the dentigerous cyst, besides simply the possibility of recurrence following incomplete surgical removal. These include:

It is of great clinical significance that numerous cases of ameloblastoma have been reported developing in the wall of dentigerous cysts from the lining epithelium or associated epithelial rests (Fig. 4-3). Stanley and Diehl have reviewed a series of 641 cases of ameloblastoma and have found that at least 108 cases of this neoplasm, approximately 17%, were definitely associated with an impacted tooth and/or a follicular or dentigerous cyst. The disposition for neoplastic epithelial proliferation in the form of an ameloblastoma is far more pronounced in the dentigerous cyst than in the other odontogenic cysts. The formation of such a tumor manifests itself as a nodular thickening in the cyst wall, the mural ameloblastoma, but this is seldom obvious clinically. Therefore, it is not only good clinical practice, but also an absolute requisite that all tissue from dentigerous cysts be submitted to a qualified oral pathologist for thorough gross and microscopic examination. In reviewing the histologic changes sought by the oral pathologist which occur in the dentigerous cyst as a premonitory manifestation of ameloblastoma, Vickers and Gorlin have stressed that hyperchromatism of basal cell nuclei, palisading with polarization of basal cells and cytoplasmic vacuolization with intercellular spacing of the lining epithelium, when observed together, are manifestations of impending neoplasia. These findings may occur individually in other rather harmless conditions. The presence of sprouting or budding and protruding of epithelial islands from lining epithelium has been claimed to be evidence of neoplastic transformation, but this in itself was not considered such an indication by Vickers and Gorlin.

The development of epidermoid carcinoma from the lining epithelium of the dentigerous cyst also has been adequately documented in the literature reviewed by Gardner, who reported eight acceptable cases among 25 cases of carcinoma developing in odontogenic cysts of all types combined. Browne and Gough have reported two additional cases of malignant transformation in dental cysts and suggested that keratin metaplasia in long-standing cyst lining appears to precede the development of the carcinomatous change, although there is little evidence that the odontogenic keratocyst is associated with malignant change more commonly than other types of odontogenic cysts. The predisposing factor and mechanism of development of this malignancy are unknown, but its occurrence appears unequivocal (Fig. 4-4).

Finally, the development of a mucoepidermoid carcinoma, a type of salivary gland tumor, is less well documented than the epidermoid carcinoma of this origin, but it also appears to be a potentiality. The inclusion of normal salivary gland tissue in the posterior portion of the body of the mandible has been reported, and undoubtedly, some central salivary gland tumors in this location originate from this source. However, cases of central mucoepidermoid carcinoma (q.v.) have been discovered in association with dentigerous cysts involving impacted mandibular third molars, and considering the frequency with which mucus-secreting cells are found in this lining epithelium indicative of the pluripotentiality of this epithelium, this very distinct possibility must always be considered. These findings comprise most of the medical rationale for removal of impacted third molars with pericoronal radiolucencies; however, impacted teeth with small pericoronal radiolucencies (suggesting the presence of normal dental follicle rather than dentigerous cyst) also may be monitored with serial radiographic examination. Any increase in the size of the lesion should prompt removal and histopathologic examination. Any lesion that appears larger than a normal dental follicle indicates removal and histopathologic examination.

Clinical Features

Shear (1992) had recorded a 0.8% frequency. It is likely that they occur more frequent clinically and as some rupture spontaneously, these cysts go unnoticed and are not submitted for histological examination.

These cysts are found in children of different ages, and occasionally in adults if there is delayed eruption. Deciduous and permanent teeth may be involved, most frequently anterior to the first permanent molar. Clinically, the lesion appears as a circumscribed, fluctuant, often translucent swelling of the alveolar ridge over the site of the erupting tooth. When the circumcoronal cystic cavity contains blood, the swelling appears purple or deep blue; hence the term ‘eruption hematoma’. It is usually painless unless infected.

Sometimes more than one cyst may be present. There is often a brief history of about three to four weeks duration during which they enlarge to approximately 1–1.5 cm.

Radiographic Features

It may show a soft tissue shadow since the cyst is confined within it and there is usually no bone involvement.

Histologic Features

The superficial aspect is covered by the keratinized stratified squamous epithelium of the overlying gingiva. This is separated from the cyst by a strip of dense connective tissue of varying thickness which usually shows a mild chronic inflammatory cell infiltrate. Inflammatory cell infiltration is common. The follicular connective tissue is more densely cellular, less collagenous and has a basophilic hue, presumably because of a higher content of acid mucopolysaccharide in the ground substance. Odontogenic epithe-lial cell nests may be present in the connective tissue.

In noninflamed areas, the epithelial lining of the cysts is characteristically of reduced enamel epithelial origin, consisting of two or three cell layers of squamous epithelium with a few foci where it may be a little thicker. The adjacent corium is hyperemic and is the seat of a chronic inflammatory cell infiltrate (Fig. 4-5).

Treatment

No treatment is necessary as the cyst often ruptures spontaneously. Surgically exposing the crown of the tooth may aid the eruption process.

Clinical Features

The largest and most detailed series of cases of odontogenic keratocyst has been published by Brannon, and his data are probably most representative of this lesion. The cyst may occur at any age, from the very young to the very elderly, although Brannon found it to be exceedingly rare under the age of 10 years, there being only two such patients in his series of 283 persons. The peak incidence is in the second and third decades of life, with a gradual decline thereafter. The data of Browne (104 patients) and of Forssell (119 patients) are virtually identical. In all series, there is a predilection for occurrence in males, ranging from 1.44:1 (Brannon), 1.46:1 (Browne) to 1.79:1 (Forssell).

The mandible is invariably affected more frequently than the maxilla: in the series of Brannon, 65% versus 35%, in the series of Browne, 79% versus 21%, and in that of Forssell, 78% versus 22%. In the mandible, the majority of the cysts occur in the ramus-third molar area, followed by the first and second molar area and then the anterior mandible. In the maxilla, the most common site is the third molar area followed by the cuspid region.

Multiple odontogenic keratocysts occur with some frequency. Lesions found in children are often reflective of multiple odontogenic keratocysts as a component of the nevoid basal cell carcinoma syndrome. However, at other times, these multiple cysts are independent of the syndrome. A rather remarkable parallelism between the odontogenic keratocyst and the ameloblastoma with respect to mean age of occurrence, predilection for site of occurrence, radiographic findings and recurrence rate has also been pointed out by Browne.

There are no characteristic clinical manifestations of the keratocyst, although about 50% of the patients in Brannon’s series were symptomatic prior to seeking treatment. Among the more common features are pain, soft-tissue swelling and expansion of bone, drainage and various neurologic manifestations such as paresthesia of the lip or teeth. The maxillary OKC tends to be secondarily infected with greater frequency than the mandibular ones, due to its vicinity to the maxillary sinus.

Radiographic Features

Radiographically most OKCs are unilocular, presenting a well-defined peripheral rim. Scalloping of the border is also a frequent finding and this represents variations in the growth pattern of the cyst. Multilocular radiolucent OKC is also observed, generally representing a central cavity having satellite cysts. When it is multilocular and especially if located in the third mandibular molar area, it may be confused radiographically with an ameloblastoma. Occasionally OKC may mimic a dentigerous cyst and contain the crown of a retained tooth within its lumen. The final diagnosis of any cystic cavity within the jaw bones will be achieved only after biopsy of the surgical specimen. Multilocularity (20%) is often present and tends to be seen more frequently in larger lesions. Most lesions, however, are unilocular, with as many as 40% noted adjacent to the crown of an unerupted tooth (dentigerous cyst position). Approximately 30% of maxillary and 50% of man-dibular lesions produce buccal expansion. Mandibular lingual enlargement is occasionally seen. Proximity to the roots of adjacent normal teeth sometimes causes resorption of these roots, although displacement is more common. Sometimes these cysts displace the neurovascular bundle.

Histologic Features

The odontogenic keratocyst wall is usually rather thin unless there has been superimposed inflammation. The lining epithelium is highly characteristic, and is composed of:

Histologically, these cysts are formed with a stratified squamous epithelium that produces orthokeratin (10%), parakeratin (83%), or both types of keratin (7%). No rete ridges are present; therefore, the epithelium often sloughs from the connective tissue (94% of the time). The epithelium is thin, and mitotic activity is frequent; therefore, OKC grows in a neoplastic fashion and not in response to internal pressure. In the presence of an intense inflammatory process, the adjacent epithelium loses its keratinized surface, may thicken and develop rete processes or may ulcerate.

The connective tissue wall often shows small islands of epithelium similar to the lining epithelium; some of these islands may be small cysts. In at least some cases, the apparent islands of epithelium and small satellite or ‘daughter’ cysts actually represent the ends of folds of the lining epithelium of the main cystic cavity which have been cut in cross-section; the linings of these cysts are very commonly folded. Forssell and his associates have studied this problem using serial sections of cysts and found microcysts in the wall in 20% and epithelial islands in 50% of their cases. In 35% of the cases, apparent microcysts were found to be part of the main cyst by the serial sections while pseudo islands of epithelium were found in 75% of the cases.

The lumen of the keratocyst may be filled with a thin straw colored fluid or with a thicker creamy material. Sometimes the lumen contains a great deal of keratin, while at other times it has little. Cholesterol, as well as hyaline bodies at the sites of inflammation, may also be present. The electrophoretic measurement of fluid from these cysts has been reported by Toller to show that it contains a very low content of soluble protein compared with the patient’s own serum (Fig. 4-6).

Dysplastic and neoplastic transformation of the lining epithelium in the odontogenic keratocyst is an uncommon occurrence but has been reported. Of the 312 keratocysts studied by Brannon, only two exhibited cellular atypia. Occasional other cases have also been described in the literature. Areen and his associates have recently reported a case of epidermoid carcinoma developing in an odontogenic keratocyst, and in reviewing the literature, have emphasized the necessity for careful microscopic examination of all such cysts.

The variant of OKC that produces only orthokeratin acts somewhat differently than other OKCs. These almost always are found in a dentigerous association, usually around the mandibular third molar, and they are much less aggressive. They do not have a hyperchromatic basal layer; in fact, the basal layer is flattened. They are not associated with basal cell nevus syndrome (orthokeratinized odontogenic cyst).

Finally, the highly characteristic nature of the parakeratinized lining epithelium and its relationship to the high recurrence rate have been emphasized by a report dealing with orthokeratinized odontogenic cysts and their recurrence rate. Wright investigated 59 cases of orthokeratinized odontogenic cysts and found that they showed a predilection for occurrence in males, most commonly in the second to fifth decades. These cysts were located predominantly in the posterior mandible, where they most typically appeared as dentigerous cysts. The thin, uniform lining epithelium was covered with orthokeratin and showed a prominent granular layer and a cuboidal to flattened basal layer. Follow-up of 24 of these patients revealed only one case of recurrence. This difference in biologic behavior would further underscore the necessity for very strict application of the definition of the term odontogenic keratocyst in diagnosis of the lesion (Fig. 4-7).

Treatment and Prognosis

The odontogenic keratocyst should be surgically excised. However, clinical experience has shown that complete eradication of the cyst may be difficult because the wall of the cyst is very thin and friable and may easily fragment. In addition, perforation of cortical bone, particularly in lesions involving the ramus, is common and this complicates total removal.

The most important feature of the odontogenic keratocyst is its extraordinary recurrence rate. This has been reported as being between 13 and 60%. A review of 763 cases of odontogenic keratocysts in 13 different reported series of cases has shown the average recurrence rate to be 26%, with the majority occurring within five years of the surgical procedure. Forssell, Forssell and Kahnberg (1988) observed that recurrences were more frequent (63%) with cysts in patients with the nevoid basal cell carcinoma syndrome than with cysts in patients without the syndrome (37%). Keratocysts enucleated in one piece recurred significantly less often than cysts enucleated in several pieces, and the recurrence rate in cases with a clinically observable infection, a fistula or with a perforated bony wall was higher. The size of the cyst did not seem to influence its prognosis after surgery, but those whose radiographic appearance was multilocular had a higher recurrence rate than those with a unilocular appearance.

Browne found no significant differences in recurrence rate following three basic methods of treating the lesions:

Furthermore, recurrence does not appear related to the presence of satellite cysts. On this basis, Browne concluded that recurrence of the keratocyst is due to the nature of the lesion itself, i.e. the presence of additional remnants of dental lamina from which a cyst may develop, and is not related to its method of treatment. Since recurrence may be long delayed in this lesion, follow-up of any case of odontogenic keratocyst with annual radiographs is essential for at least five years after surgery. It is also essential that patients with an odontogenic keratocyst, especially if multiple, be evaluated medically to rule out the possibility of the jaw cyst-basal cell nevus-bifid rib syndrome (q.v.).

Clinical Features

The syndrome is very complex and includes a great variety of possible abnormalities. These may be briefly summarized as follows:

Some of these patients have shown a lack of response to parathormone as judged by the lack of phosphate diuresis which, coupled with shortened fourth metacarpals in some patients, has suggested that there may be some relationship to pseudohypoparathyroidism.

Oral Manifestations

The odontogenic keratocysts are indistinguishable from those previously described by that term which are not associated with this syndrome (Fig. 4-8). Because they often develop early in life, deformity and displacement of developing teeth may occur. However, they may not develop until middle age even though the basal cell skin tumors have occurred early in life.

Treatment and Prognosis

Several cases of ameloblastoma have developed in cysts of this syndrome, thus emphasizing the importance of surgical removal of the cysts and their histologic examination. Whenever a diagnosis of odontogenic keratocyst is received by the dentist, he must be certain to rule out the presence of this syndrome because of the many associated problems which these patients ultimately will face.

Clinical Features

Occasionally these dental lamina cysts in infants become sufficiently large to be clinically obvious as small discrete white swellings of the alveolar ridge, sometimes appearing blanched as though from internal pressure (Fig. 4-9A). These probably correspond to those structures described in the older literature as the ‘predeciduous dentition’. These lesions appear to be asymptomatic and do not seem to produce discomfort in the infants.

Histologic Features

These are true cysts with a thin epithelial lining which lacks rete processes and show a lumen usually filled with desquamated keratin, occasionally containing inflammatory cells (Fig. 4-9B). Interestingly, dystrophic calcification and hyaline bodies of Rushton (q.v.), commonly found in dentigerous cysts, are also sometimes found in this lesion.

Treatment

No treatment is required inasmuch as these lesions almost invariably will disappear by opening onto the surface of the mucosa or through disruption by erupting teeth.