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Calcifying odontogenic cyst

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CALCIFYING ODONTOGENIC CYST: CONTROVERSIES, CLINICAL FEATURES, HISTOPATHOLOGY & TREATMENT

AUTHOR: Sanketh DS, MDS

INTRODUCTION & ETIOLOGY

Calcifying odontogenic cyst (COC) was first described by Gorlin in 1962. It is a cystic lesion which histologically shows an ameloblastomatous lining along with ghost cells and focal calcifications. COC is thought to arise from the reduced enamel epithelium surrounding the unerupted crown or from the remnants of the dental lamina.

CONTROVERSIES – CYST OR TUMOR?

Since this lesion was first described, there has been much confusion with regards to the nature or behavior of this lesion and its terminology. Reports have shown this lesion to have sufficient variation in its clinical behavior and histopathological features.

a) This has led to confusions, as to whether this lesion could be a cyst, a tumor, a cystic tumor or a lesion encompassing cystic variant and a tumor variant.
b) This lesion has also been termed calcifying cystic odontogenic tumor, calcifying ghost cell odontogenic tumor, dentinogenic ghost cell tumor, calcifying odontogenic lesion and ghost cell cyst.

Before we get into further details, let us brush through some basics so that we can better understand what this confusion is all about and where this lesion stands in the most recent WHO classification (2017) of odontogenic cysts and tumors.

A cyst is defined as a pathological cavity, lined by epithelium, having fluid, semifluid or gaseous content that are not created by the accumulation of pus. Cysts usually have a lumen, an epithelial layer lining the lumen and a cyst wall or capsule that basically comprises the connective tissue. A tumor however is a term that usually represents a neoplasm – benign or malignant and is used to describe any solid tissue enlargement. Hence tumors are solid neoplastic growths unlike cysts and do not possess a lumen.

So, is COC an odontogenic cyst or a tumor?

Well, the 1971 and the 1992 WHO reports classified this lesion under the odontogenic tumor category. Interestingly, though classified as a tumor, the report described the lesion to be a non-neoplastic cystic lesion fuelling confusion. However, the 1992 report went on to state that the terms dentinogenic ghost cell tumor or odontogenic ghost cell tumor could be proposed for certain variants of this lesion showing a solid growth with ameloblastomatous lining, ghost cells and dentinoid.

Later in the 2005 WHO report, this lesion was described as a benign cystic tumor or a cystic neoplastic lesion. This meant that though the lesion was cystic, its nature was that of a benign neoplastic tumor. The consensus report did not consider it to be a non-neoplastic cyst! Hence the lesion was retained under the tumor category, but it was renamed as calcifying cystic odontogenic tumor. Its solid variant dentinogenic ghost cell tumor however, was considered to be a distinct entity on its own.

However, the most recent WHO report in 2017, states that most of the COC lesions are cystic in nature and rarely are they solid tumors. Also they have a clinical course that is not aggressive and rarely recur. Hence, the report states that there is sufficient evidence to deem these cystic lesions as simple developmental cysts and not tumors. Pathologists have agreed to go back to the lesion’s previous terminology and call it calcifying odontogenic cyst. They have also categorized it as a developmental odontogenic cyst! So, as per the most recent reports, COC stands to be a developmental cystic lesion classified under Odontogenic Cysts!

CLINICAL FEATURES

COC does not have a gender predilection and usually affects individuals in the 2nd to 4th decades of life. The maxilla and mandible have an equal predilection but COC most often occurs in front of the molars in the incisor-canine region. Clinically the lesion usually presents as a swelling with a hard bony expansion. Individuals may rarely have pain and displacement of teeth. COC may sometimes be extra-osseous and occur in the gingiva. Such lesions are around 4cm in diameter, pink-red in colour, resemble fibromas and are smooth elevated masses occurring often in the incisor-cuspid region.

RADIOGRAPHIC FEATURES

COCs are unilocular lesions whose margins can be well circumscribed or poorly defined. They may on occasions also show multilocular lesions. One third to half the cases are associated with irregular radiopacities. Sometimes the lesions are associated with odontomes in which case radiopacities could be denser. There may be tooth displacement, root resorption and expansion of cortical plates. The extra-osseous lesions may cause superficial resorption of bone manifesting as saucer-shaped radiolucencies.

HISTOPATHOLOGY

The histology features of COC are pretty characteristic and are quite straight forward to diagnose.

In fact, this was the definition of COC given in the WHO 1992 classification:

“A cystic lesion in which the epithelial lining shows a well-defined basal layer of columnar cells, an overlying layer that is often many cells thick and that may resemble stellate reticulum, and masses of “ghost” epithelial cell that may be in in the epithelial lining or in the fibrous capsule. The “ghost” epithelial cells may become calcified. Dysplastic dentine may be laid down adjacent to the basal layer of the epithelium, and in some instances the cyst is associated with an area of more extensive dental hard tissue formation resembling that of a complex or compound odontoma.”

Oh yes, that is quite a huge definition, but this pretty much sums up the histology features of the lesion. So, let’s break this definition down to smaller chunks in order to understand the histology features.

“A cystic lesion in which the epithelial lining shows a well-defined basal layer of columnar cells, an overlying layer that is often many cells thick and that may resemble stellate reticulum…”

COC is a cystic lesion, hence there would be a lumen lined by an epithelial lining, which is basically a palisaded layer of columnar cells with the nuclei polarized away from the basement membrane. And the overlying layer of cells are pretty much epithelial cells too, but are separated from each other due to intercellular oedema. In fact they look very similar to the stellate reticulum seen during the cap stage of tooth development. Also to be noted is that this epithelial lining very much resembles that seen in ameloblastoma.

“and masses of “ghost” epithelial cell that may be in in the epithelial lining or in the fibrous capsule. The “ghost” epithelial cells may become calcified.”

Ghost cells are basically eosinophilic epithelial cells that lack nuclei or cellular organelles. In fact these cells may or may not retain their cellular outline, become enlarged or ballooned, fuse with each other and form amorphous sheets of eosinophilic material. No one still knows the nature of these cells. While there is a hypothesis that states ghost cells may be a result of abnormal keratinization, there are also theories which propose that these cells may be a phenomenon of coagulative necrosis or abnormal accumulation of enamel proteins. These cells have an affinity for calcification.

“Dysplastic dentine may be laid down adjacent to the basal layer of the epithelium, and in some instances the cyst is associated with an area of more extensive dental hard tissue formation resembling that of a complex or compound odontoma.”

There may sometimes be deposits of hyalinised eosinophilic material deposited below the epithelium. This is called dysplastic dentine or dentinoid. It is thought to be dentin like material that arises as a result of an inductive effect of the odontogenic epithelium on the connective tissue. This is pretty much like ameloblasts inducing the dental papilla cells to become odontoblasts, which then secrete dentin. In some instances COC may be associated with odontomas, which could be seen histologically as sheets of eosinophilic or calcified material.

TREATMENT AND PROGNOSIS

COC is usually treated conservatively by surgical enucleation and the prognosis is very good. The lesion also very rarely shows recurrence. COC sometimes, could arise in association with an odontoma, for which the treatment would still be conservative.

REFERENCES

Shear M, Speight PM. Cysts of the Oral and Maxillofacial regions.4th ed. Blackwell Munksgaard;2007.

Speight PM, Takata T. New tumour entities in the 4th edition of the World Health Organization Classification of Head and Neck tumours: odontogenic and maxillofacial bone tumours. Virchows Arch. 2018 Mar;472(3):331-339.

Kramer I, Pindborg J, Shear M (1992) WHO International Histological Classification of Tumours. Histological typing of odontogenic tumours, 2nd edn. Springer-Verlag, Berlin.

Barnes L, Eveson JW, Reichart P, Sidransky D (2005) Odontogenic Tumours. Ch 6, WHO classification of tumors: pathology and genetics of head and neck tumours. IARC, Lyon.

Reichart PA,  Philipsen HP. Odontogenic tumors and allied lesions. Quintessence Publishing; 2004.

Oral and Maxillofacial Pathology.Neville,Damm,Allen,Chi. South Asian Edition.

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