Lateral periodontal cyst: a case report and literature review.

BACKGROUND: The lateral periodontal cyst is considered a developmental odontogenic cyst with unusual occurrence. In most cases it is preliminary diagnosed as a radiographic finding, presenting as well circumscribed or as a round or teardrop-shaped radiolucent area. Due to its location it can easily be misdiagnosed as a lesion of endodontic origin. Final diagnosis should be based on histopatological examination. The purpose of this paper is to report a classic case of lateral periodontal cyst located in the anterior region of mandible and to review the relevant literature which describes the clinical, radiological and histopathological features of lateral periodontal cysts.
METHODS: A 50 years female patient complained of an asymptomatic gingival swelling in the region between the left mandibular lateral incisor and canine. Radiographic examination revealed a well circumscribed radiolucency with approximately 0.5 cm diameter with a radiopaque margin between the roots of the left mandibular lateral incisor and canine. The adjacent teeth had vital pulp.
RESULTS: A total enucleation of the lesion was performed, and intraoperative examination showed a single lesion with no communication between the cyst's cavity and the oral environment. Histological examination revealed that the lesion was "lateral periodontal cyst of developmental origin". There was no recurrence or complications for 24 months follow-up.
CONCLUSIONS: The lateral periodontal cyst can be considered in the differential diagnosis when a radioloucent lesion appears adjacent to the roots of vital teeth. The treatment of choice is surgical removal and subsequent histological evaluation to confirm the diagnosis. Relapses are infrequent.

INTRODUCTION

Odontogenic cysts are classifed by the World Health Organization as infammatory and developmental according to their epithelial lining. Lateral periodontal cysts (LPC) have been regarded as an independent condition [1-4].

LPCs are defined as nonkeratinized and noninflammatory developmental cysts located adjacent or lateral to the root of a vital tooth. This cyst's most frequent location is at the level of mandibular premolars but it has been reported occurring in the other areas [5].

LPC is one of the cysts of lower incidence among developmental odontogenic cysts. Since pain or other clinical symptoms have seldom been reported, the lesion is often discovered on routine radiographic examination. Radiographs of the lateral periodontal cyst show a well-circumscribed round or ovoid radiolucent area, usually with a sclerotic margin. Most of them are less than 1 cm in diameter [5-8].

Histologically, the lateral periodontal cyst is a distinct type of developmental cyst characterized by a thin, nonkeratinized epithelium usually 1 to 5 cell layers thick, which resembles the reduced enamel epithelium. The epithelial lining exhibits focal thickenings or plaques, in which clear glycogen-containing epithelial cells have often been found. The connective tissue subjacent to the epithelium exhibits a zone of hyalinization [9].

It presents unique characteristics and there is an important differential diagnosis with lesions of endodontic and periodontal origin, and other cysts from the same group [5-8]. The pathogenesis of LPC, the gingival cyst of the adult, the botryoid odontogenic cyst and the glandular odontogenic cyst may be correlated [1]. Some authors, based on the clinical and morphological similarities, reinforce that the gingival cyst of the adult and LPC present a common histogenesis, and these lesions may have the same extra-osseous and intra-osseous characteristics, respectively [10].

This paper reports a classic case of LPC which is located in the anterior region of mandible, and also presents a brief literature review of the clinical, radiological and histopathological features of LPC.

CASE DESCRIPTION AND RESULTS

A 50 year old black female patient was referred to São Paulo State University - UNESP, São José dos Campos Dental School, Department of Biosciences and Oral Diagnosis, São José dos Campos, São Paulo, Brazil, complaining of mandibular left lateral incisor mobility. The patient reported that she had used the stick to tooth in this region, shortly before the change was observed, approximately six months ago.

Clinical examination revealed mild horizontal mobility of the tooth #32. The palpation of vestibular surface of the alveolar process in the region of teeth #32 and #33 was asymptomatic. Vitality test demonstrated vital pulp of teeth #32 and #33.

Periapical radiograph of the site was taken. Radiographic examination revealed a well-circumscribed, unilocular, radiolucent area with approximately 0.5 cm in diameter adjacent to the roots of the left mandibular lateral incisor and canine (Figure 1).

Figure 1

Periapical radiograph showing circumscribed radiolucent area located between two vital teeth #32 and #33.

On the basis of these findings, a clinical diagnosis of lateral periodontal cyst was made. Local anaesthesia was used and full-thickness mucoperiosteal flap was elevated. The cyst capsule was detached from the adjacent bone. A total enucleation of the lesion was realized using a surgical curette (Figure 2).

Figure 2

Photograph showing bone cavity after enucleation of the cystic lesion.

After enucleation, the cyst was histologically examined (Figure 3A). Histological sections showed a single cavity lesion lined by epithelium of variable thickness, sometimes displaying one or two layers of cuboid cells and sometimes showing areas that formed thick clusters of cells more voluminous in the midst of which several PAS positive clear cells were observed. The capsule consisted of fibrous tissue with several bleeding areas and absence of inflammation (Figure 3 B, C and D). The histological findings supported the diagnosis of lateral periodontal cyst of developmental origin.

Figure 3

A = Photograph showing macroscopic aspects of the lesion.

B = Histopathologic view of the lesion shows one cystic cavity only; the capsule of fibrous tissue showed several bleeding areas and absence of inflammation (hematoxylin and eosin stain, original magnification x25).

C = Histopathologic view of the lesion shows epithelium lining rich in cells with glycogen (hematoxylin and eosin stain, original magnification x100).

D = Histopathologic view of the lesion shows PAS positive clear cells (PAS x100).

Follow-up of the case, twenty four months after operation, showed uneventful healing and spontaneous regeneration of bone in periapical radiography.

DISCUSSION

LPC is considered as developmental odontogenic cyst with unusual occurrence that may be associated with vital teeth. LPC represents approximately 0.8% to 2% of all odontogenic cysts [1,9]. Literature review shows that the LPC is more prevalent in adults in the 5th - 7th decades, with mean age of 52 years, without preference for race or sex. The most frequently reported location of LPC is the mandibular premolar area, followed by the anterior region of maxilla (Table 1) [5,6,8,11-20]. In most cases the LPC does not present distinctive clinical symptoms; the associated teeth are vital, unless secondarily infected. Hence, the PLC is often discovered on routine radiographic examination.

Table 1

Data from clinicopathological studies of Lateral periodontal cyst (LPC)

Study	N	Gender	Mean age(years)	Race	Location
Krier 1980	1	Male	37	Caucasian	Mandible
Cohen et al. 1984	24	Male: 12Female: 12	54	Caucasian: 13Nigerian: 11	Mandible: 18Maxilla: 6
Rasmusson et al. 1991	32	Male: 21Female: 11	55	Not reported	Mandible: 28Maxilla: 4
Buchner et al. 1996	1	Male	38	Nigerian	Mandible
Carter et al. 1996	25	Male: 13Female: 12	46	Caucasian: 13Nigerian : 8Not reported: 4	Mandible: 21Maxilla: 4
Tolson et al. 1996	1	Male	50	Nigerian	Mandible
Meltzer JA 1999	1	Female	73	Caucasian	Mandible
Kerezoudis et al. 2000	2	Male: 2	58	Caucasian	Mandible: 1Maxilla: 1
Mendes et al. 2006	2	Male: 1Not reported: 1	59	Not reported	Mandible: 2
Ortega et al. 2007	1	Male	31	Not reported	Maxilla
Nart et al. 2007	1	Female	74	Caucasian	Mandible
Formoso Senande et al. 2008	11	Male: 6Female: 5	37	Not reported	Mandible: 3Maxilla: 8
Nikitakis et al. 2010	2	Male: 1Female: 1	61	Caucasian	Mandible: 1Maxilla: 1

The pathogenesis of LPC may be related to the three etiopathological hypotheses: reduced enamel epithelium [9], remnants of dental lamina [11] and cellular remnants of Malassez [1]. The first hypothesis is that the cyst is lined by nonkeratinized epithelium reminiscent of the reduced enamel epithelium which is supported by PCNA immunohistochemical expression. The second theory is related to dental lamina remnants, based on the fact that LPC histopathologically presents glycogen-rich clear cells, which is also seen in the dental lamina. The third hypothesis offered that the epithelial remnants of Malassez presented in the roots surface, principal location of the LPC, play a role.

The diagnosis of LPC should be restricted to cysts that are located in the periodontal side. Differentiation between the original lesion and inflammatory cysts and keratocystic odontogenic tumours should be based on clinical, radiographic and pathohistological findings [9,11,21].

Radiographically, the cyst presents as a well circumscribed round or teardrop-shaped radiolucent area (generally not exceeding 1 cm in diameter) with a radiopaque rim, located laterally to the root of a vital tooth. The periodontal ligament space as a rule is not enlarged and there must not be a communication between the cyst's cavity and the oral environment [5,11,12,19-21]. Occasionally, LPC may be multicystic, and called as odontogenic botryoid cyst due to macro- and microscopic features resemble to "bunch of grapes" (from the Greek word "botrios") [11,12,21,22].

The radiographic features may be inconclusive relative to the diagnosis. Other interradicular radiolucencies must be distinguished from the LPC: anatomic radiolucencies, such as the mental foramen, maxillary sinus and the nutrient canals; cyst of pulpal origin, other cysts of the jaws, odontomas and other tumours. It may resemble a cyst that develops laterally through a side channel accessory in a non vital tooth [6,12]. In a retrospective study of injuries of no endodontic origin, 3.8% cases of LPC responsible for various treatments without success were found [6].

The histopathology revealed that LPC is a developmental cyst characterized by a thin layer of nonkeratinized epithelium with a thickness of 1 - 5 mm, which resemble the reduced enamel epithelium. Nonkeratinized squamous epithelium is composed of 1 - 5 layers of cells displaying a palisade distribution. The epithelium lining can be rich in epithelial plaques composed of the clear fusiform cells rich in glycogen. Some areas of the epithelial thickening, referred to as plaques or theca, are commonly found, and the connective tissue subjacent to the epithelium exhibits a zone of hyalinization. Inflammation is not a feature and the walls of the cyst consist of mature collagen fibrous tissue [10,12,21]. However, it is possible to observe the histopathological variant of LPC - botryoid cyst, that should receive a greater attention considering the rate of recurrence [14,18,23,24] and unusual presentation [25,26]. The botryoid cyst represents a histopathological variant which presents with multilocular cystic "grape-like" appearance in the bone. Histopathological findings shows multiple cystic spaces lined by nonkeratinized stratified squamous epithelium [14,24-26].

The mobility of mandibular lateral incisor and canine reported by the patient can be justified by the cyst growth. However, LPC does not reach proportions that are larger than 1 cm [10,12,21] while cysts of inflammatory origin tend to grow continuously. In cases of a vital tooth, LPC can still be clinically confused with cysts that develop in inflammatory processes in cases of advanced periodontal disease, where the presence of periodontal inflammation stimulates epithelial proliferation. In most cases the differential diagnosis must be established with radicular cysts, in a view of their high frequency. These lesions are characterized by necrosis of the affected tooth, as a result of which vitality testing proves negative. Follicular or dentigerous cysts are always associated to an impacted tooth (particularly a lower third molar), while primordial cysts are mostly located in the ascending mandibular ramus. Authors suggest the investigation of the possibility of LPC causing isolated bone defects [27].

It is interesting to know that the soft tissue variant of LPC corresponds to gingival cyst of the adult [28]. Some authors state that both lesions have the same histogenesis [15,28]. Adult gingival cysts present the same histogenesis, location and clinical features as LPCs, though the rests of odontogenic epithelium appear in the soft tissues - not in bone as in the case of LPCs. As a result, there are no radiological findings [15].

Finally, the importance of diagnosis is especially related to the differential diagnosis with keratocystic odontogenic tumour due to its aggressive and infiltrative growth leading to high recurrence rates which requires a more invasive treatment. The keratocystic odontogenic tumour is one of the most aggressive odontogenic tumours due to its relatively high recurrence rate, relatively fast growth, and the tendency to invade adjacent tissues; it has been reported that it can penetrate even the skull base [29]. Scharfetter et al. [30] demonstrated both: slowly and rapidly proliferating areas in different parts of the keratocystic odontogenic tumour epithelium and the connective tissue wall. He suggested that the invasive growth of keratocystic odontogenic tumour probably resulted from active growth of the connective tissue wall. Other possible explanations for its high recurrence are increased fibrinolytic activity in the cyst wall, increased mitotic activity, epithelial proliferation in the connective tissue, and a residual dental lamina with subsequent new cyst formation [29]. The bone resorption by the cyst is mediated by activation of osteoclast-like cells [31] and/or biologically active collagenases [32].

The enucleation is the treatment for LPC, which can often be done without injury to adjacent teeth [13,17]. The recurrence is not common; it has been reported with the botryoid variant [33].

CONCLUSIONS

The lateral periodontal cyst can be considered in the differential diagnosis when a radioloucent lesion appears adjacent to the roots of vital teeth. A histological study is essential in order to confirm the diagnosis. The treatment of choice is surgical removal and subsequent histological evaluation to confirm the diagnosis. Relapses are infrequent.