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The fourth edition of the World Health Organization classification of head and neck tumours summarizes changes in odontogenic and maxillofacial tumours and reintroduces a chapter on odontogenic cysts that reclassifies calcifying odontogenic cystic tumours as calcifying odontogenic cysts based on lack of evidence to substantiate them as true neoplasms. This article presents an unusual case report of a calcifying odontogenic cyst treated successfully with enucleation in support of the view of recent classification.
CPD/Clinical Relevance: Calcifying odontogenic cysts are rare entities that can be managed successfully by enucleation, supporting the WHO position that these cysts are not neoplasms.
Article
Parmanand Dhanrajani
The term calcifying odontogenic cyst (COC) was first used by Gorlin et al in 19621,2,3 to describe a new odontogenic cystic entity with a peculiar pathogenesis and histological features. In 1971 and again in 1992,4,5,6,7 the World Health Organization (WHO) listed this entity and described it as:
A non-neoplastic cystic lesion in which epithelial lining shows a well-defined basal layer of columnar cells, an overlying layer that is often many cells thick that may resemble stellate reticulum, and masses of ghost cells that may be in the epithelial cells lining the cyst or in the fibrous capsule. The ghost cells may become calcified. Dysplastic dentin may be laid down next to the basal cell layer of the epithelium.
With time, it became apparent that not all COC were cystic. Some, in fact, appeared as solid neoplasms.8 To encompass both the cystic and non-cystic variants of this lesion, some authors suggested a change in the name originally proposed by Gorlin et al 1962.1 Fejerskov and Krogh9 proposed the term ‘calcifying ghost cell odontogenic tumour’, while Friedman et al10 suggested that the lesion should be classified as a cystic calcifying odontogenic tumour.
In 1981, Praetorius et al8 tried to resolve the classification for calcifying odontogenic cysts by dividing them into two entities: a cyst and a neoplasm. The cystic entity was further subdivided into simple unicystic, unicystic odontoma-producing and cystic amelo-blastomatous proliferating types. For the neoplastic counterpart, they proposed the term dentinogenic ghost cell tumour.
Based on these controversies, in 2005, the WHO7 defined COC as a benign cystic tumour arising from odontogenic epithelium with ectomesenchyme, which may be associated with the formation of hard tissue and termed as a calcifying cystic odontogenic tumour (CCOT). The epithelial lining of a COC appears to have the ability to induce the formation of dental hard tissue in the adjacent connective tissue wall. Other odontogenic tumours, such as ameloblastoma, ameloblastic fibroma, and ameloblastic fibro-odontoma may be associated with this lesion.11 It is widely accepted that those COCs that have features of odontogenic tumours develop these secondarily, rather than as an initial phenomenon in the pre-existing odontogenic tumours.
In 2017,12,13 the WHO reclassified CCOT as COC and included it in the group of odontogenic and non-odontogenic developmental cysts. This decision was based on a lack of evidence for neoplastic behaviour. In 2008, an international collaborative study had reviewed the WHO classification of ghost cell lesions and showed that just under 90% were either entirely cystic or associated with an odontoma, lesions for which there is no justification for being classified as neoplastic.14
This article presents a case of COC as a chance finding on histological examination, which was treated conservatively, mimicking a follicular cyst associated with a lower impacted third molar and highlights its relation and importance to the recent WHO reclassification.
Report of a case
A 22-year-old female was referred to the oral and maxillofacial clinic, HCF Dental Centre, Sydney, Australia, complaining of recurrent pain and discomfort with her wisdom teeth. She was medically fit and well, and not on any medication.
On examination, the left lower third molar showed mild pericoronitis. There was no sign of infection in the other areas. The orthopantomogram revealed impacted UR8, UL8, LR8 and LR8 were absent (Figure 1). UR8 and LL8 each had an associated radiolucency consistent in appearance with follicular tissue. LL8 and LR8 were mesially inclined.
Figure 1. Orthopantomogram showing impacted UR8, LL8 and LR8 with radiolucency around.
The patient was advised that surgical removal of the wisdom teeth with enucleation/curettage of the follicular tissue was required. She consented for the procedure under general anaesthesia.
The procedure was uneventful and she recovered well. The biopsy report from UR8 was consistent with follicular tissue; LL8 was reported, unexpectedly, as inflamed calcifying odontogenic cyst.
The histopathologiy report described the following: ‘irregular pieces of inflamed fibrous connective tissue lined most of its part with non-keratinized squamous epithelium of varying thickness. The epithelium shows spongiosis and inflammatory cell exocytosis. There are areas of individual cell keratinization with formation of ghost cells with foci of calcification. The fibrous connective tissue contains deposits of eosinophilic dentinoid, islands of odontogenic epithelial cell rests and chronic inflammatory cell infiltrate. The features are consistent to inflamed calcifying odontogenic cyst’ (Figures 2 and 3).
Figure 2. Photomicrograph showing ghost cell in the epithelial lining. (Haematoxylin–eosin stain; original magnification x200.)Figure 3. Photomicrograph showing areas of calcification in epithelium. (Haematoxylin–eosin stain; original magnification x200.)
The post-operative phase was uneventful, and there was no recurrence during 2 years of follow-up.
Discussion
Calcifying odontogenic cysts are uncommon lesions, with a low prevalence among all odontogenic cysts. They are usually asymptomatic, seen commonly in the anterior mandible, but less frequently in the posterior region where they are associated with impacted teeth. The male to female ratio is even, and there is no age predilection.
There are no clinical presentations or pathognomonic radiological signs for this lesion. It is only histological findings that allow differentiation of COC from the other cystic lesions of the jaw.
At the earliest stages of COC presentation, radiological presentation can be similar to dentigerous cysts, odontogenic keratocysts and/or unicysctic ameloblastomas because all have very little or no mineralization.
It has been reported that some odontogenic cysts occur in association with odontogenic tumours. Because neoplastic and hamartomatous lesions can occur at any stage of odontogenesis, odontogenic tumours with combined features of epithelial and mesenchymal components may arise within odontogenic cysts. COC frequently occur in association with other odontogenic tumours such as ameloblastomas, ameloblastic fibromas or complex odontomes.16
Ennucleation is the widely accepted treatment of choice to manage COC, recurrence rate is very low and long-term prognosis is good.
There has been a reported case of malignant transformation arising from recurrent COC.17 The malignant variant mentioned in previous WHO classifications was a dentinogenic ghost cell tumour, which does not appear in the newer classification.12,13
The main aim of this article was to present a case report in support of the present view of COC as a cystic lesion rather than a neoplasm, based on the recent WHO classification.
The questions this and similar cases raise are whether it is justified to continue using the term calcifying odontogenic cyst for these similar lesions, and whether these should these be treated as cysts or neoplasms. Based on the case reported here, it is justified to use the term calcifying odontogenic cyst, rather than neoplasm, and to base treatment on the assumption that it is a cyst. Although this an isolated single case, it supports the view that the lesion is cystic. There continues to be a lack of evidence in the literature, both clinical and histological, to support the classification of the lesion as a neoplasm.
There have been similar presentations of calcifying odontogenic cyst mimicking as follicular lesion in the literature.18,19 These were also diagnosed on histological examination.
Conclusion
In conclusion, calcifying odontogenic cysts are rare, often asymptomatic odontogenic lesions, and are identified incidentally on orthopantomography and histological findings. Calcifying odontogenic cysts can occur within the follicle of an impacted tooth. A case of calcifying odontogenic cyst was presented that was managed successfully with enucleation, supporting the recent WHO view being a cystic lesion not a neoplasm.
