Author: Sanketh DS, MDS
Odontogenic keratocyst (OKC), is so named because 1) the cyst is odontogenic in origin and 2) the epithelium produces so much keratin, that it accumulates in the cystic lumen. The feature that makes odontogenic keratocyst distinct as compared to other odontogenic cysts, is its biological behaviour! OKCs may exhibit clinically aggressive behaviour, a significant rate of recurrence and association with nevoid basal cell carcinoma syndrome or Gorlin’s syndrome.
OKC, as the name implies, arises from the odontogenic epithelium. It is believed to develop from 2 different sources of epithelium them being,
a) The remnants of the dental lamina.
b) Extension of the basal cells from the overlying the epithelium.
The theory of OKC being derived from the remnants of dental lamina is generally more accepted.
However, there is also research which advocates the development of OKCs from basal cells of the overlying epithelium. These studies demonstrated, the overlying basal cells dropping off from the overlying epithelium and attaching to the cysts through fenestrations in the bone! Researchers called these as “basal cell hamartias” or “basal cell off-shoots”
CYST OR TUMOR
Ok….a quick question! Is odontogenic keratocyst really a cyst… or is it, in any way, a benign tumor? Now, this may seem to be a silly question at first but, it is one of the most hotly debated topics in the field of Oral Pathology. So…why this confusion?
Researchers have considered a number of reasons to reclassify OKC as a tumor.
1. OKC has an aggressive, destructive behaviour.
2. OKCs are known to have a greater growth potential than other odontogenic cysts. While cysts like radicular or dentigerous cysts may enlarge as a result of an increased osmotic pressure within the cystic fluid, the same doesn’t imply for OKCs. Their growth is attributed to an inherent genetic potential of the epithelium and enzymatic activity in the wall of the cyst.
3. Genetic mutations of tumor suppressor genes, most important being PTCH1 and P53, give OKC a greater growth potential than other cysts.
4. Also, its proliferative potential is further proved by immune-histochemical studies which reveal an increased level of certain proteins like PCNA, P53 and Ki67.
5. OKC has a very high recurrence rate.
In fact, the 2005 WHO monograph on Head and Neck Tumors, lists OKC under tumors and has been given the name Keratocystic Odontogenic tumor (KCOT)! In spite of this reclassification, there are pathologists who do not agree with this proposal.
“Odontogenic keratocyst (OKC) has been reinstated as the preferred term for this simple keratinising cyst……. at the present time, there was insufficient evidence to support a neoplastic origin of the odontogenic keratocyst. It was decided therefore that odontogenic keratocyst remains the most appropriate name for this lesion, and keratocystic odontogenic tumour (KCOT) was removed from the classification.”
– WHO Consensus group (2017)
Reference: 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. 2017;472(3):331-339.
OKCs may occur at any age, ranging from very young to elderly. It frequently occurs in the second and third decades of life with a slight male predilection. The mandible is more prone to be affected than the maxilla, especially the third molar-ramus area. OKCs may be small or large, with the smaller ones usually being asymptomatic, and being diagnosed during routine radiographic examination. Large OKCs may cause swelling, facial asymmetry, pain and drainage.
A characteristic feature of OKCs is that most of the cysts have an antero-posterior growth pattern, within the medullary cavity of the bone without causing bone expansion. This is often a clinical and radiographic cue to the diagnosis as other cysts of the same size may show a bony expansion.
Patients with multiple OKCs must be evaluated for nevoid basal cell carcinoma syndrome or the Gorlin’s syndrome.
OKCs are mostly unilocular in appearance with a well corticated border. Certain lesions, however may show scalloped borders. Most large lesions, occurring in the posterior mandible are multi-locular. At-least 25-40 % of the cases have a radiographic appearance similar to the dentigerous cyst, with a peri-coronal radiolucency around an un-erupted tooth. Resorption of roots is rare with OKC although displacement of teeth is more common. The radiographic appearance of OKC is not diagnostic and is often diagnosed by its typical histopathological features. OKC may radiographically mimic many lesions like, ameloblastoma, dentigerous cyst, unicystic ameloblastoma, radicular cyst and lateral periodontal cyst.
Microscopically, the epithelial lining is composed of a
1. Stratified squamous epithelium usually 6-10 cells in thickness.
2. Corrugated or wavy parakeratinized layer.
3. Cuboidal to columnar basal cell layer, that is palisaded, described as having a picket fence or tomb stone appearance. The nuclei of the basal cells are oriented away from the basement membrane.
The fibrous wall/connective tissue is usually devoid of inflammation and may harbour satellite cysts, cord or islands of odontogenic epithelium. The epithelium-connective tissue interface is flat and has no rete ridges. Focal areas may show detachment of the epithelium from the connective tissue. In the presence of intense inflammation, the overlying epithelium may lose its characteristic features, wherein parakeratinization and the palisading of basal layer are lost. Also, the epithelium may develop rete ridges. The lumen may contain a clear fluid or a cheesy material that represents keratin under the microscope.
TREATMENT AND PROGNOSIS
OKCs are aggressive, have a high recurrence rate and hence need to be completely removed. Many reports indicate an average of 30 % recurrence for OKC. Multiple recurrences are not rare, particularly large OKCs occurring in the posterior mandible.
OKCs may recur due to the fact that enucleation procedures may be incomplete and new cysts may develop due to the retained satellite cysts and odontogenic islands or rests. Also, the epithelial lining is thin and friable, and may be difficult to remove when cysts are large. The left over epithelium may give rise to the development of a new cyst. Another reason investigators believe to give rise to recurrence are the basal cell offshoots or the basal cell hamartias, where the basal cells of the adjacent epithelium may be responsible.
These factors emphasise the need to carefully remove the lesion in total. Hence many surgeons perform a peripheral ostectomy rather than enucleation. Surgeons also advocate chemical cauterization of the bone after removal of the cyst. Decompression are also performed, by inserting a drainage tube after cystotomy, which subsequently reduces the size of the cyst to facilitate easy removal with lesser recurrence.
The overall prognosis for OKC is good barring a few sporadic aggressive cases. There is a possibility for malignant transformation although the chances are extremely low.
Cysts of oral and maxillofacial regions. Shear and Speight. 4th Edition.
Shafer’s Textbook of Oral Pathology.Rajendran and Sivapathasundaram.6th Edition.
Oral and Maxillofacial Pathology.Neville,Damm,Allen,Chi. South Asian Edition.
Oral Pathology: Clinicopathologic correlations.Regezzi,Sciubba,Jorda.5th Edition.
Contemporary Oral and Maxillofacial Pathology, Sapp,Eversole,Wysoki.2nd Edition.
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