Keratocystic Odontogenic Tumor

An odontogenic keratocyst is a rare and benign but locally aggressive developmental cyst. It most often affects the posterior mandible and most commonly presents in the third decade of life. Odontogenic keratocysts make up around 19% of jaw cysts.Intermediate magnification of an odontogenic keratocyst showing a folded cyst.Intermediate magnification of an odontogenic keratocystHigh magnification of an odontogenic keratocyst. An odontogenic keratocyst is a rare and benign but locally aggressive developmental cyst. It most often affects the posterior mandible and most commonly presents in the third decade of life. Odontogenic keratocysts make up around 19% of jaw cysts. In the WHO/IARC classification of head and neck pathology, this clinical entity had been known for years as the odontogenic keratocyst; it was reclassified as keratocystic odontogenic tumour (KCOT) from 2005 to 2017. In 2017 it reverted to the earlier name, as the new WHO/IARC classification reclassified OKC back into the cystic category. The WHO/IARC classification no longer considers it a neoplasm, because the evidence supporting that hypothesis (for example, clonality) is considered insufficient. However, this is an area of hot debate within the head and neck pathology community, and some pathologists still regard OKC as a neoplasm despite the reclassification. Peak incidence during second and third decades of life. At least 50% of odontogenic keratocysts are found in posterior part and lower ramus of the mandible. Swelling is the most common presenting complaint; however, OKCs may be asymptomatic and found incidentally on dental radiographs. Rarely symptoms can arise due to infection or expansion of the bone. Odontogenic keratocysts originate from the odontogenic epithelium (dental lamina) in the alveolus left from tooth development stages. They are mainly thought to arise from rests of Serres. Sporadic (non-syndromic) and syndromic OKCs are associated with mutations in the gene PTCH found on chromosome 9q, which is part of the Hedgehog signaling pathway. PTCH is a tumour suppressor gene. Loss of PTCH activity leads to a brake in the cell cycle. A third of OKCs show mutations in PTCH, resulting in the cyst epithelium undergoing highly proliferative activity. This leads to growth of the cyst wall and when removed favours recurrence if following incomplete removal of the epithelium. Multiple odontogenic keratocysts are a feature, and major diagnostic criteria, of nevoid basal cell carcinoma syndrome (NBCCS, also known as Gorlin-Goltz Syndrome). Almost all individuals with NBCCS have odontogenic keratocysts which require numerous treatments. Consideration of the syndrome needs to be taken into account if found in children or if multiple OKCs are present; diagnosis of multiple OKCs in a child necessitates referral for genetic evaluation. Histologically, the cysts are indistinguishable to non-syndromic cysts and over 80% will have PTCH mutations. Diagnosis is usually radiological. However, definitive diagnosis is through biopsy. Aspirational biopsy of odontogenic keratocysts contains a greasy fluid which is pale in colour and contains keratotic squames. Protein content of cyst fluid below 4g% is diagnostic of odontogenic keratocysts. Smaller and unilocular lesions resembling other types of cysts may require a biopsy to confirm the diagnosis. On a CT scan, the radiodensity of a keratocystic odontogenic tumour is about 30 Hounsfield units, which is about the same as ameloblastomas. However, ameloblastomas show more bone expansion and seldom show high density areas. Radiographs of odontogenic keratocysts show well-defined radiolucent areas with rounded or scalloped margins which are well demarcated. These areas can be multilocular or unilocular. The growth pattern of the lesion is very characteristic from which a diagnosis can be made as there is growth and spread both forward and backward along the medullary cavity with little expansion. No resorption of teeth or inferior dental canal and minimal displacement of teeth is seen. Due to lack of expansion of the odontogenic keratocyst, the lesion can be very large when radiographically discovered.