Keratocystic Odontogenic Tumor
Synonym / Acronym
KCOT (formerly Odontogenic Keratocyst (OKC))
Keratocystic odontogenic tumor (KCOT) is a benign neoplasm that has keratinized epithelial lining and a very high recurrence rate. KCOT develops from cells originating from the dental lamina. The method of enlargement is thought to be mostly by proliferation of the lining and the osmotic pressure is less of a factor for enlargement than in the case of other dental cysts. This mechanism of growth has led to moving keratocystic odontogenic tumor from the cystic category (known as OKC) to the benign tumors category under the name KCOT. Multiple KCOTs are a characteristic of basal cell nevus syndrome (Gorlin’s syndrome).
KCOT occur in a wide range of age and have peak incidence between the second and third decade of life. The male to female ratio is 1.3:1. The mandible is affected as twice as the mandible and most commonly found in the mandibular third molars and ramus areas. KCOT can form around unerupted tooth. It is usually painless and it gets secondarily infected. Maxillary cysts are noted chiefly in the molars area. It has a great potential for recurrence after surgical removal due to the presence of small satellite cysts or fragments left after surgical removal.
Well-defined radiolucency with smooth margins and thin radiopaque borders is seen. It may have round, oval or scalloped borders. KCOT is mostly unilocular but can be multilocular in larger lesions. The internal structure is mostly completely radiolucent and sometimes thin septa can be seen giving the look of a multilocular lesion. Over 40% of the unilocular lesions are associated with crown of unerupted tooth resembling a dentigerous cyst. KCOT has the tendency to extend along the bone rather than expanding it; thus there may be extensive involvement of the body of the mandible and ramus before any expansion occurs. This contributes to their late detection. They can displace and resorb teeth but to a lesser extent than dentigerous cysts. KCOT can displace the mandibular canal inferiorly and can occupy the entire maxillary sinus.
KCOT that is associated with crown on unerupted tooth may be indistinguishable from a dentigerous cyst. If it is connected apical to the CEJ or if there is no expansion then it is most likely a KCOT. The multilocular appearance and scalloped margin can resemble an ameloblastoma although ameloblastoma has a great potential for expansion. KCOT can resemble an odontogenic myxoma when it is multilocular and has mild expansion. Although simple bone cyst has scalloped margins and minimal expansion which can resemble KCOT; however, a simple bone cyst margins are harder to detect. When multiple KCOT are detected, it likely to be associated with basal cell nevus syndrome (Gorlin’s syndrome).
Since KCOT has a great potential to recur, a Cone Beam CT examination can best detect the extensions of the margins, thus referral to a radiologist for complete radiographic examination is recommended. In case of basal cell nevus syndrome where multiple KCOTs can be found, a full radiographic examination should be carried out to determine the number, size, location and extensions of the lesion.
Surgical treatment can include resection, curettage, and marsupialization to reduce size of the lesion. Completely remove the walls of the cyst is important due high recurrence rate of KCOT. Periodic follow-up every 6 months is recommended to monitor the patient for any signs of recurrence which can develop within first 5 years or delayed to 10 years.
HISTORY: An 18-year-old female patient was referred for Cone Beam CT scan for evaluation of her right posterior mandible s/p marsupialization of an odontogenic cyst.
FINDINGS: There is a well-defined radiolucent lesion in the right posterior mandible. The lesion has a hydrostatic outline. The lesion measures 5.5 cm x 3 cm x 2 cm withth a well-defined corticated border. The lesion is expansile and has cause thinning of the cortical borders. The mandibular canal has been displaced buccal to the periphery of the lesion. The lesion is associated with the crown of impacted tooth #32 and has displaced the tooth posteriorly and superiorly into the ascending ramus. There might be slight root resorption in tooth #31.
IMPRESSION: The radiographic signs of expansion, hydrostatic form and association with crown of an impacted tooth are consistent with a dentigerous cyst. Keratocystic odontogenic tumor can be included as well. Ameloblastoma is a possibility but less likely as it causes extensive roots resorption at this size.
HISTORY: A 74-year-old male patient was referred for Cone Beam CT scan for evaluation of #32 region for recurrence of keratocystic odontogenic tumor.
FINDINGS: There is a well-defined corticated lesion in the area of #31 and #32. The lesion extends from the alveolar crest to the inferior border of the mandible at its greatest extent. Tooth #32 is missing. There is slight superior and linugla expansion. There are no signs of root resorption or displacement of tooth #31. The mandibular canal is displaced inferiorly. There is slight cortical thinning of the mandibular inferior cortex.
IMPRESSION: Recurrent KCOT. No significant changes from previous panoramic image.
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HISTORY: A 13-year-old female patient was referred for Cone Beam CT scan for evaluation of the left mandible regarding a keratocystic odontogenic tumor.
FINDINGS: There is a well-defined and largerly corticated radiolucent lesion in the left mandible. The mesial aspect of the lesion is the apex of the displaced tooth #22 and extends posteriorly to the apex of tooth #19. The superior border of the lesion is at the alveolar crest and extends inferiorly to the inferior border of the mandible. There is displacement of teeth and tooth #21 appears to have some tooth resorption.
The lesion has displaced the mandibular canal inferiorly. There is prominent buccal expansion and thinning of the buccal cortical border. The margins appear mostly intact, although radiographically there is no evidence of continuity of the buccal cortex in the anterior aspect of the lesion. This maybe the result of volume averaging. The lesion measures approximately 3.5 cm antero-posteriorly and 2.5 cm supero-inferiorly at its greatest dimensions. The bulk of the lesion appears unicystic, the margins of the lesion suggests a multilocular expansile pattern (arrows).
FINDINGS: The findings are consistent with KCOT.
FINDINGS: The dentition development is consistent with the patient’s age of 16 years. There is a well-defined radiolucent lesion in the right posterior mandible. The lesion borders are smooth and corticated. The lesion extends from the mesial root apex of tooth #30 to the ramus area and from the alveolar crest superiorly to about 5 mm above the inferior cortex. It measures 3 cm L x 2 cm H x 1.5 cm W. The lesion has displaced tooth #31 and pushed tooth #32 posteriorly and superiorly in the ramus area. There is slight expansion in the superior aspect of the cortex. Axial slice and cross-sections show thinning of buccal and lingual borders. The mandibular canal has been traced and can be seen displaced inferiorly and is very close to the inferior cortex. The lesion is proximate but distinct from the canal except in the region of the 3rd molar where a distinct canal cortex is not evident. The alveolar crest is absent in the region between #31 and #32. Root resorption is not evident.
IMPRESSION: The signs are consistent with the biopsy of KCOT.
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