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Central calcifying odontogenic cyst. A review of the literature and
the role of advanced imaging techniques
JH Erasmus1, IOC Thompson2, LJ van Rensburg3,4 and AJ van der Westhuijzen1
1
Departments of Oral and Maxillofacial Surgery, 2Oral Pathology and 3Oral and Maxillofacial Radiology, Oral and Dental Teaching
Hospital, University of Stellenbosch, Tygerberg; 4Bellville, Panorama, Republic of South Africa
The central calcifying odontogenic cyst (CCOC) is a rare lesion. This paper reports a new case,
reviews the clinical, histomorphological and radiographic features reported in the literature and
describes the CT and MRI features of this new case. We postulate that, as part of an
evolutionary process, cystic COCs originate as unilocular lesions but may later become
multilocular. The role of advanced imaging and histology in the diagnostic process are
discussed.
Keywords: tomography, x-ray computed; magnetic resonance imaging; odontogenic cysts;
diagnostic imaging
Introduction
Report of a case
The central calcifying odontogenic cyst is a rare lesion.
Its clinical and radiological features are not pathognomonic,1,2 and it is characterized by histological
diversity. Radiographically, it presents as a unilocular
or, occasionally, multilocular radiolucency that may
contain calci®ed radiopacities or tooth-like densities.
Unilocular lesions are therefore compatible with
dentigerous, radicular or residual cysts, while multilocular lesions may resemble ameloblastomas or
odontogenic keratocysts.
The correlative diagnostic imaging and histological
®ndings of some odontogenic tumours and cysts have
been reported in the recent literature3 ± 6 In these cases,
while CT displayed aspects of bone morphology not
visible on plain ®lms, MRI provided essential
macropathlogical detail which correlated well with the
histological ®ndings. The features identi®ed by these
combined imaging techniques are helpful in differentiating cysts from other neoplastic lesions and can thus
alter surgical management.
The purpose of this report is to present a calcifying
odontogenic cyst that occured in the anterior region of
the mandible, to review the relevant literature and to
describe its CT and MRI features, which has to our
knowledge, have not been reported before.
A 29-year-old female was referred to the Department
of Oral and Maxillofacial Surgery, Faculty of
Dentistry, University of Stellenbosch with a painful
swelling in the anterior mandible that had been present
for approximately 1 year.
No unusual features were noted on extra-oral
examination. Intraorally, there was a well-de®ned ®rm
swelling, of 3.562 cm, with a smooth surface on the
lingual aspect of the anterior mandible. The lesion
extended from the right lateral incisor to the left canine
and ¯uctuation of the thinned, expanded lingual cortex
could be demonstrated. The mucosa overlying the lesion
was intact. The right central incisor, both left incisors
and the left canine did not react to cold or electrical
stimulation and the left central and lateral incisors were
mobile. There was no buccal expansion or paraesthesia
of the lower lip. Her medical history was noncontributory.
Radiographic examination disclosed a well-de®ned
unilocular radiolucency of the anterior mandible,
extending transsymphyseally from the right lateral
incisor to the left canine. Root resorption of both the
left central and lateral incisors was evident. (Figures 1
and 2). A single calci®ed focus was noted on the
occlusal view (Figure 2).
The di€erential clinical diagnosis included cystic
ameloblastoma and odontogenic keratocyst.
CT and MRI were performed to characterize the
lesion further. Five mm thick axial CT scans with both
soft tissue and bone algorithms showed a wellcorticated, partially septated, predominantly lingually
expansile cystic lesion in the anterior mandible,
Correspondence to: Dr JH Erasmus, Faculty of Dentistry, University of
Stellenbosch, Private Bag X1, Tygerberg 7505, South Africa
Received 2 May 1997, accepted 23 September 1997
Calcifyng odontogenic cyst
J Erasmus et al
31
measuring 362 cm. Although the lingual cortex was
very thin there was no loss of continuity. The cyst
contents measured 26 Houns®eld units consistent with
a ¯uid more dense than water (Figure 3).
MRI at 0.5 tesla included T2-weighted FSE
images (long TR/TE, 4725/120 ms) and T1-weighted
(short TR/TE, 520/25 ms) SE images before and
after intravenous gadolinium-DTPA (`Magnevist'1
0.1 mmol/kg) Schering, Berlin, Germany).
On T2-FSE images the cyst contents displayed an
homogenous high signal intensity, similar to cerebrospinal ¯uid (CSF). The incomplete septum was clearly
identi®ed on the T2 FSE images and displayed uptake
of the contrast by the overlying epithelium on T1weighted images (Figures 4 and 6). The major
component of the cyst extended into the left sublingual
space but there was no extraosseous spread. (Figure 4).
On short TE/TR images (T1-weighted) the cyst
contents displayed a degree of T1 shortening and
appeared isointense with muscle, indicative of a high
protein content (Figure 5). Short TE/TR (T1-weighted)
images showed uptake of contrast in the lining
epithelium which was of varying thickness (Figure 6).
However, no calci®cations were identi®ed on either CT
or MRI. A plexiform follicular ameloblastoma was
considered the most likely diagnosis.
L
Figure 1 Cropped panoramic radiograph showing a well de®ned
unilocular radiolucency of the anterior mandible. Root resorption of
the left central and lateral incisors is evident
Figure 3 Axial 5 mm CT Scan shows bony septum anteriorly (arrow
A) and the well corticated lingual expansion (arrow B)
Figure 2 Oblique occlusal radiograph showing the thin lingual
expansion, root resorption of the left central and lateral incisors and
a small nonspeci®c linear shaped calci®ed focus in relation to the left
lateral incisor. This opacity could be identi®ed retrospectively on the
panoramic radiograph
Figure 4 Axial 5 mm T2-Fast Spin Echo MR scan showing the
lesion ®lled with homogenous, high signal intensity ¯uid extending
into the left sublingual space, and the incomplete septum, anteriorly
Calcifyng odontogenic cyst
J Erasmus et al
32
Figure 7 Photomicrograph of the cyst wall showing the odontogenic
epithelial lining with sheets of ghost cells (original magni®cation
6200)
Figure 5 Axial 5 mm T1-SE MR image showing the cyst contents
isointense with muscle
Figure 8 Photomicrograph showing sheets of ghost cells with areas
of calci®cation (original magni®cation 6200)
Figure 6
Axial 5 mm T1-SE MR image scan following the
administration of contrast showing the varying thickness of the
enhanced epithelium
The cyst was enucleated under general anaesthesia
and con®rmed the imaging ®ndings. The non-vital
teeth were endodontically treated. The postoperative
course was uneventful. Histological examination
con®rmed the diagnosis of calcifying odontogenic cyst.
Discussion
An incisional biopsy was performed under local
anaesthesia. Histological examination showed a cystic
lesion with a ®brous capsule lined by odontogenic
epithelium of varying thickness. The basal cells of the
epithelium were predominantly columnar with features
similar to those of ameloblasts, while the overlying cells
were more loosely arranged resembling stellate reticulum.
(Figure 7). Sheets of eosinophilic ghost cells with areas of
calci®cation were a prominent feature. (Figure 8).
Dysplastic dentine (dentinoid) was observed in the
connective tissue adjacent to the epithelium and the
capsule contained a chronic in¯ammatory cell in®ltrate.
The lesion was diagnosed as a calcifying odontogenic cyst.
Epithelial-lined cysts seldom occur in skeletal bones,
because embryonic epithelial rests are normally not
found in them. They do, however, occur in the jaws
where the majority are lined by epithelium derived
from remnants of the odontogenic apparatus. These
odontogenic cysts are classi®ed as either of developmental or in¯ammatory origin.7 The calcifying odontogenic cyst (COC) is a rare example of a developmental
odontogenic cyst.
Gorlin and colleagues (1962)8 were the ®rst to
describe this entity. They initially regarded it as the
oral analogue of the cutaneous calcifying epithelioma
of Malherbe but later labelled it the calcifying
Calcifyng odontogenic cyst
J Erasmus et al
33
odontogenic cyst. Prior to this, Rywkind (1932)
described it as a variant of the cholesteatoma, while
Maitland (1947)10 regarded it as a type of ameloblastoma. The COC has also been reported under a variety
of other designations including: dentinogenic ghost cell
odontogenic tumour,11 epithelial odontogenic ghost cell
tumour,12 ghost cell cyst,13 calcifying ghost cell
odontogenic tumour,14 and dentino-ameloblastoma.15
The WHO presently describe the calcifying odontogenic cyst as a non-neoplastic cyst, but classify it as a
benign tumour.16 Langlais and colleagues (1995)17
proposed the term calcifying odontogenic lesion
(COL), which encompasses both the cystic and
tumorous forms as well as combined lesions containing elements of both.
The odontogenic origin of the COC is widely
accepted.18 Praetorius et al11 suggested that it develops
in the dental follicle, gingival tissue or bone from
remnants of either odontogenic epithelium or reduced
enamel epithelium. The pathogenesis is, however, still
controversial.15 While it is accepted that the epithelial
lining may induce the production of dentinoid or an
odontoma, the question whether COCs that have
features of other odontogenic tumours develop them
secondarily or whether the COCs are themselves a
secondary phenomenon in pre-existing odontogenic
tumours, is still unresolved.19 The former concept is
widely accepted,13 but several investigators still support
the latter possibility.20 ± 22
The majority of COCs arise centrally in bone, but
several peripheral (extraosseous) examples have been
reported,20,23,24 Both central and peripheral forms occur
with equal frequency in the maxilla and mandible.7,24,25
The majority of lesions are located in the incisor-canine
area.25 The COC comprises between 0.37 ± 2.1% of all
odontogenic tumours.8,15,24,26 The peripheral variant
comprises 13 ± 25% of the COCs.7,20,23 Praetorius et
al11 reported a bimodal age distribution, with peaks in
the second and sixth decades. The odontomaassociated type occurred at an earlier age (17 years),
while the neoplastic variant was more common in older
patients.7 Buchner found an almost equal gender
distribution.25 The highest prevalence occurred in the
second and third decades, with a mean age of 30.3
years.
The central COC presents as an asymptomatic hard
swelling of the jaws that produces expansion rather
than erosion of bone.24,25 Pain indicates secondary
infection.23 Early lesions are usually detected following
routine radiographic examination and they are often
associated with an unerupted tooth.1,27 The peripheral
COC presents on the gingiva as a non-speci®c wellcircumscribed sessile or pedunculated mass with a
smooth surface. They resemble other epulides such as
gingival ®bromas or peripheral giant cell granulomas.24
The de®nitive diagnosis of COC is made histologically, due to the lesion's lack of characteristic clinical
and radiological features, as well as its variable
biological behaviour. Cystic and solid variants of
COCs are described with the cystic variant comprising
the majority of cases.15,18,25,28,29 The histological features
of the COC are complicated by its frequent association
9
with other odontogenic tumours, such as the complex
or compound odontoma, ameloblastoma, odontoameloblastoma, ameloblastic ®broma, ameloblastic
®bro-odontoma and the adenomatoid odontogenic
tumour.15,18,21,25,26,29 Five malignant tumours have been
reported.11,20,30,31 The associated tumour rather than the
cyst determines the biological behaviour of these
lesions21,23 This histological diversity together with it's
variable clinical behaviour illustrate the unusual nature
of this lesion and has resulted in di€erent classifications.11,25 Many authors accept the classi®cation
developed by Praetorius et al11 in an analysis of 16
cases (Table 1). Buchner25 recognized the multicystic
COC as a separate entity in an excellent review of 215
cases of central COCs and proposed a more detailed
classi®cation that encompass all reported clinical and
pathological variations of this lesion (Table 2).
Enucleation is the preferred mode of treatment for
simple cystic lesions, but, when an odontogenic tumour
co-exists, the tumorous part of the lesion determines
the type of treatment.11 Recurrence is unusual. Only
nine cases have been reported and all recurred within 8
years.25 A follow-up period of at least 10 years is,
therefore, recommended.
According to Buchner's classi®cation25 this lesion
would be classi®ed as a central multicystic COC (type
B 1a). The classi®cation of Praetorius does not
recognise multicystic lesions as a separate entity.
The presence of radiopacities could suggest a
diagnosis of an adenomatoid odontogenic tumour, a
calcifying epithelial odontogenic tumour or an ameloblastic ®bro-odontoma.1 Nagao and colleagues21
reported in a series of 23 cases only three cases of
multilocular lesions, which converts to a ratio of 7.6 : 1.
In 33% of cases COCs are associated with unerupted
Table 1 Classification of calcifying odontogenic cysts proposed by
Praetorius et al11
Type
Description
1a
1b
1c
2
Simple unicystic type with little or no dentinoid
Odontoma producing type
Ameloblasomatous proliferating type
Neoplastic variant (dentinogenic `ghost' cell tumor)
Table 2 Classification of calcifying odontogenic cysts proposed by
Buchner25
Type
Description
A
Peripheral (extraosseous) COC
Cystic variant
Neoplastic (solid) variant
Central (intraosseous) COC
Cystic variant
Simple (unicystic or multicystic)
Associated with an odontoma
Associated with odontogenic tumours (other than
odontoma)
Other variants (such as clear cell variant,
pigmented variant)
Neoplastic (solid) variant
Malignant COC
B
1
(a)
(b)
(c)
(d)
2
3
Calcifyng odontogenic cyst
J Erasmus et al
34
teeth.7 Root resorption or root divergence may also be
observed. The peripheral COC rarely exhibits radiographic bony involvement, but it may causes super®cial
erosion of the underlying bone.24,28
CT complements conventional radiographs by
depicting the anatomy and topography more accurately. Lesions can be characterized as cystic or solid
by virtue of Houns®eld attenuation values. The intraand extraosseous extent of lesions are more accurately
determined. Axial sections are invaluable in the
assessment of lesions that are situated in the
symphysis of the mandible. Conventional and panoramic ®lms provide insucient detail in this area.32 In
our case the use of CT virtually excluded the OKC as a
di€erential diagnosis because it lacked the generally
accepted features, namely a thick, sclerotic margin, a
cloudy lumen and minimal cortical expansion.17
MRI produces multiplanar, superior imaging of the
soft tissues without exposing the patient to radiation. It
accurately di€erentiates between cysts and solid
tumours. Cyst contents can be characterized as ¯uid,
keratin or blood degradation products.32 With MRI the
margins of cystic lesions can be accurately evaluated
for possible soft tissue extension; T2-weighted images
re¯ect tumour-tissue margins most accurately.33 Fibrous or incomplete ossi®ed septa and mural nodules
can be demonstrated. The latter may be the only
diagnostic clue that a mural ameloblastoma is arising
in a pre-existing dentigerous cyst. MRI is regarded as
superior to CT in the evaluation of mandibular lesions,
because it can depict both cortical and medullary
involvement.33
The histological nature of the lesion and age of the
patient are important factors in recurrence of the COC.
Wright and co-workers34 noted that four recurrent
cases occured in patients over the age of 60. The
histology of three recurrent cases was documented: one
solid neoplastic tumour,7 one mixed cystic and solid
COC associated with an odontoma34 and one cystic
lesion.35
In this case the incomplete bony septum detected
with CT and MRI was an unexpected ®nding. A
similar phenomenon has been observed in ameloblastomas: MRI demonstrated that apparent incomplete
bony septa were in fact completed by soft tissue.6
Based on this observation, we postulate that cystic
COCs originate as unilocular lesions but may become
multilocular as part of an evolutionary process. The
septa are initially ®brous, but may become ossi®ed
later. Partially ossi®ed septa may, therefore, be
interpreted as an indication of a longstanding lesion.
It also implies that apparent unicystic COCs discovered
at an advanced age, may often be actual multilocular
lesions. It is possible that the recurrent cystic COCs
were multilocular, because our case demonstrated that
septa may not be evident without the help of advanced
imaging techniques. We speculate that multilocularity
underlies the role of age in recurrent cystic COCs.
Langlais et al17 stated that in some lesions of the exact
same histological tissue type, a multilocular pattern
may someday prove to be more predictive of
recurrence than a unilocular presentation. Except for
the bony septum, no other calci®cations were identi®ed
on either modality. On ®rst principles, it is expected
that MRI using conventional sequences would be
insensitive to small areas of calci®cations. Gradientecho recalled sequences should be able to detect subtle
calci®cations by virtue of increased susceptibility to
artifact.36 High resolution CT scans might also detect
more subtle calci®cations. The signi®cance of radiopaque ¯ecks or calci®cations on conventional radiographs has been addressed in the literature.17 The fact
that it may actually be septa in the process of
ossi®cation, adds more signi®cance to this plain ®lm
observation.
In conclusion, although the role of CT and MRI in
the pre-operative evaluation of this case is well
demonstrated, no characteristic features were revealed. Because the COC lacks pathognomonic
clinical, radiological, CT and MRI features, it should
be included in the di€erential diagnosis of cystic
lesions that present anterior to the ®rst molar teeth.
The plain ®lm observation of a calci®ed focus in a
radiolucent lesion can be an important clue to the
possibility of a multilocular lesion. The de®nitive
diagnosis of this lesion remains dependent on
histological evaluation.
Acknowledgements
Dr L Janse van Rensburg in the practice of Drs Schnetler,
Corbett and partners provided imaging facilities to the
Dental Teaching Hospital, University of Stellenbosch; Ms
P de Klerk, T Jonker, G Claasen, M Davids and J Hans
performed the examinations; Schering (SA) provided the
contrast material.
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