N. O. Nartey, BDS, MSc, MRCD(C),
T. Saini, BDS, MS, Dip ABOMR
King Saud University College  of Dentistry,   P.O.   Box 60169,  Riyadh  11543, Saudi Arabia.

The clinical features of ten patients with odontogenic keratocysts were studied. One patient had Gorlin-Goltz syndrome. A total of fourteen radiolucent lesions were observed on radiographic examination. All the fourteen lesions were diagnosed as odontogenic keratocyst after histopathclogical examination of biopsied tissue from the patients. The age at diagnosis ranged from 25-72 years with a mean age of 37.6 years. The male : female ratio was 2.3:1. Thirteen of these lesions occurred in the mandible, nine involved the mandibular third molar region. Involvement of the ramus of the mandible produced a sausage-shaped radiolucency. Cystic lesions which have been present for long periods of time showed scalloped margins, due to the regional resorption of the surrounding bone. The bony ledges present on the cortical bones
simulated multilocular appearance in such cases. It was also observed that the lesions in older individuals perforated the cortical plates rather than eliciting a periostally induced bony expansion.

The term odontogenic keratocyst was first coined by Philipsen1 to describe a cyst which elaborated keratin. Soon it was realized that other odon­ togenic cysts may also form keratin by metaplastic transformation of the epithelial lining. Keratocyst shows an orderly sequence of maturation of cells from the basal layer to the surface where they are discarded as complete squames into the lumen of the cyst. Pindborg and Hansen2 stressed the characteristic cyst lining which qualifies it as a sepa­ rate entity from other cystic lesions. The distinction between primordial cyst and odontogenic kerato­ cyst is controversial. Brannon,3 in his study of 312 cases of odontogenic keratocysts, found that only 44 % of primordial cysts had a lining characteristic of odontogenic keratocysts. He stressed that not all the primordial cysts are keratocysts. Soskolone and Shear,4 after reviewing 50 cases of primordial cysts, stated that the linings of all their cases demonstrated features of odontogenic keratocysts.

Forsseli and Sainio5 mentioned that the terms primordial cyst and odontogenic keratocyst have come to be used synonymously by some to the confusion of many. Shear6 supports the usage of the term primordial cyst to describe odontogenic keratocyst because of the origin of the latter from the cells of the dental lamina. The term keratocyst connotes histological features which lead to confu­ sion and fail to express the developmental nature of the lesion. The World Health Organization classifi­ cation of odontogenic cysts concur with this view.7 It recommends primordial cyst as the primary term, and odontogenic keratocyst as an alternative term.

Clinically, the cyst is known for its high recurr­ ence rate. Demonstration of low protein content in the cystic aspirate and identification of keratin squames in the smear aid in diagnosing the lesion.

Radiographically, the keratocyst does not offer a pathognomic picture. Brannon3 in his study found 61.5% of the lesions to be unilocular and 23% mul­ tilocular. The cyst has a well demarcated sclerotic margin. There may be extensive involvement of the body and the ascending ramus of the mandible, with little or no bony expansion. Scalloped margins indicating unequal growth activity may be seen in unilocular lesions and these may be misinterpreted as multilocular lesions. Larger cysts might show the presence of irregular small rounded festoons.
Main8 stated that there is the possibility of eruption of an unerupted tooth into the lumen of the cyst. This may simulate a dentigerous cyst appearance on the radiograph. He referred to them as envelop-mental cysts. Mclvor9 recognized the non-specific­
ity of the radiological appearance of the lesion. He stressed the importance of radiography to diagnose recurrence of the lesion by the presence of an enlarging corticated translucency in serial radiog­ raphs.

The present study was conducted to illustrate sig­nificant radiographic features of the lesion. Since the lesion usually has a unique clinical behavior as compared to other odontogenic cysts, its recognition at an early stage becomes of paramount clinical importance.

A review of biopsy records of the Division of Oral Pathology in the College of Dentistry at King Saud University was conducted from the beginning of 1985 till the end of 1987. The clinical radiographic features of the histologically proven cases of keratocysts were reviewed by the investigators. Fourteen lesions were observed radiographically in ten patients.

Age at the time of original diagnosis ranged from 25-72 years. The mean age was estimated to be 37.6 years. The peak incidence was found to be in the third decade.

Out of a total of ten patients, there were seven

males and three females. The male:female ratio was 2.3:1.

All cysts were found in the mandible except one which was seen in the left maxillary premolar area involving the maxillary sinus.

Two cases presented with intraoral discharging sinuses. In one case, the patient complained of salty taste in the mouth. Four patients were asymptomatic and diagnosis was made as an acci­ dental finding from examining panoramic radiog­ raphs. In two patients, there were soft tissue swel­ lings which were firm in consistency. Three cases presented with history of multiple cysts occurring in the jaws, one of them was recognized as Goriin-Goltz syndrome. The patient had undergone previ­ ous cyst enucleation in other institutions.

All cysts met the criteria of the odontogenic keratocyst. The epithelial lining was thin and uniform (5-8 cell layer thick), with corrugated parakeratotic surface. The basal cells had hyper-chromatic nuclei which were polarized away from the basement membrane.

Orthokeratinization and mild chronic inflam­ matory cell infiltrate was observed in one of the cys­ tic lining. Melanin pigmentations of the basal cell layer and excessive plasma cell infiltrates of the connective tissues were seen in some of the cystic lining.

Radiological Findings:

Eight out of the fourteen lesions involved the ascending ramus of the mandible. Five cases were found restricted to the body of the mandible. Only one cyst was seen in the maxilla in the left premolar area. The maxillary cyst displaced the floor of the sinus. None of the cysts were found to be associated with congenitally missing teeth. The neighboring teeth did not show root resorption and the lamina dura around these teeth were found to be intact in all the cases. Four cases showed cysts associated with impacted teeth but none of these cases demonstrated the typical relationship of dentigerous cysts in the radiographs [Fig. 11. The radiolucent margins were not in relationship to the cementoenamel junction.

None of the lesions demonstrated the multilocu-lar appearance. Two cases showed gross perfora­ tion of the cortical plates in the mandible [Fig. 2], Multiple keratocysts were seen in three cases, all involving the mandible [Figs. 1 and 3]. The lower border of the mandible was always found to be intact. The mandibular canal was seen to be dis­ placed and adapted to the outline of the cyst [Fig. 4]. The cystic margins were sclerotic and smooth in most of the cases or showed regional scalloping in some areas.  The cysts involving the mandible demonstrated marked extension in an anteropos­ terior direction. The buccolingual expansion was minimal as compared to the anteroposterior exten­ sion of the lesions. The cysts involved the whole ramus [Figs. 2 and 3] or the entire body of the man­ dible [Fig. 1 ] in the majority of our cases.

In this study, the age at diagnosis ranged from 25-72 years with a mean age of 37.6 years. This is in accordance with previous observations.3,10 The sex distribution of the patient population was 2.33:1 compared to 1.35:1, and 1.46:1 in Bran-non3 and Browne's4 studies, respectively. The dif­ ference in sex ratio may be due to the small sample size. Fourteen odontogenic keratocysts were observed in ten patients. All the cysts were found in the mandible except one which was seen in the left maxillary premolar area. In the mandible, eight of the lesions were located in the retromolar area. The propensity of the odontogenic keratocyst to the retromolar area of the mandible is well documented in the literature. 3,10

The odontogenic keratocyst expands by invad­ing the marrow spaces. The invasive nature of the keratocyst has lead to the belief that the lesion is a type of an odontogenic tumor rather than a cyst.11 The cystic wall of the keratocysts has been shown to elaborate bone resorbing factors.12 The quantity of the secreted osteolytic factors is less as com­ pared to those elaborated by the ameloblastoma. The keratocysts are, thus, poor bone resorbers and, hence, involve the cancellous bone in the early stages of its development. The compact bone is invaded much later. Therefore, very little expan­sion is observed in the keratocysts. In our study, the cysts demonstrated spongiosa destruction in younger individuals and cortical perforation rather than bony expansion in older individuals.

The cyst involving the ramus have propensity for the region near the anterior border of the ascending ramus above the level of the alveolar crest [Fig. 5a]. The base of the neck of the condyle, the coronoid process, the displaced cortical walls of the inferior alveolar canal, and the angle of the mandible may have a restrictive influence on the cyst in the early stages. The extension of the cyst from the ramus into the body of the mandible might be controlled by the nature of bone present apical to the last standing tooth and the cortical wails of the inferior alveolar canal. The restrictive influence of the denser bones may be responsible for the unique sausage-shape of the odontogenic keratocysts involving the ramus of the mandible.

These observations suggest that the localized cortical scalloping in certain areas and reinforcingbony ledges [Fig. 5b] will be formed as the lesion ages. This may simulate a multilocular appearance in the radiographs. As the cyst further ages, the cortical plates are completely eroded and the lining becomes continuous with the soft tissues [Fig. 5c]. The lower border of the mandible is thinned and scalloped but escapes perforation.