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Surgical Pathology of Odontogenic Cysts and Neoplasms
Steven D. Vincent and Robert A. Robinson
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The patient is a 49-year-old male with pain and swelling of the right maxilla first noticed
five days previously. Radiographs reveal a large lesion associated with an impacted maxillary right
third molar.
Dentigerous cysts are developmental odontogenic cysts. They arise in association with
impacted teeth. Their origin is from the reduced enamel epithelium between the follicle and the tooth
crown. The cyst enlarges by accumulation of fluid between the proliferating reduced enamel epithelium
and the crown. Dentigerous cysts most commonly involved the third molars, but any unerupted tooth may be
affected. They account for 25% of all jaw cysts. Dentigerous cysts are usually asymptomatic, but maybe
associated with pain, swelling and may grow so large to displace teeth or erode bone. Importantly, to the oral surgeon, clinical differentiation is frequently not possible
between dentigerous cyst, odontogenic keratocyst, and unicystic ameloblastoma. The radiographic
features of dentigerous cysts are those of lesions with well circumscribed, corticated borders. They are
usually unilocular. The radiographs are not diagnostic and differentiation from odontogenic keratocyst
and unicystic ameloblastoma is not possible using this modality either.
Microscopically, dentigerous cysts have a nonkeratinized stratified squamous epithelial lining which
may have occasional sebaceous or mucus cell metaplasia. There is often a thick fibrous connective tissue
wall. Inflammation can be minimal or marked. The histologic differential diagnosis includes periapical
(radicular) cyst. These cysts are inflammatory and not developmental. They arise when epithelium around
the root is stimulated by inflammation. The histopathologic features may be identical to dentigerous
cysts, therefore the radiographic or clinical description of the cyst is required. Very rarely,
dentigerous cysts may develop an ameloblastoma or develop dysplastic epithelium and evolve into squamous
carcinoma.
The treatment of dentigerous cyst is curettage and removal of the unerupted tooth.
A 17 year old female complains of tenderness for one week in the left posterior aspect of
the mandible. Radiographs show a well circumscribed radiolucency of the right mandibular body and ramus
involving an unerupted third molar.
Odontogenic keratocysts are developmental and arise from epithelial rests of dental
lamina. 75% of odontogenic keratocysts are located in the posterior body of the mandible and ramus. They
may occur in the maxilla with extension into the maxillary sinus. One of the pathologic pitfalls
associated with maxillary odontogenic keratocysts is their underdiagnosis when they present as maxillary
sinus cystic lesions. Squamous lined cysts of the maxillary sinus should be evaluated very carefully for
the histologic features of odontogenic keratocyst. Clinically odontogenic keratocysts may be
asymptomatic or can be large and cause tooth resorption and cortical plate expansion.
The histologic findings are those of a thin, squamous keratinized lining, usually 6-10 cells thick,
although this number can be variable. The epithelium can be parakeratinized (by far the most common) or
be orthokeratinized. (Figure 4). Importantly, the basal layer is palisaded. (Figure 3). Keratocysts
may become inflamed and in that case the squamous lining is thickened and the histologic features can be
altered to the point that they appear as inflamed dentigerous cysts. The palisaded basal layer may only
be seen in a small portion of the cyst and thus it is important to examine the entire specimen. As a
general rule, all odontogenic cysts should be submitted in their entirely for histologic examination.
Orthokeratinizing keratocysts are much less common than those that are parakeratinizing. As their
name implies, there is marked orthokeratosis rather than parakeratosis but there is also no palisaded
basal layer either. (Figure 4) Orthokeratinizing keratocysts should classified as such because their
rate of recurrence after curettage or enucleation is very low, probably 5% or less.
The recurrence rate of the more common (parakeratinizing) keratocyst is up to 30%. Of note, older
literature refers to keratocysts as either parakeratinizing keratocysts or orthokeratinizing keratocysts.
Newer references tend to drop the word "parakeratinizing" for odontogenic keratocysts that are not
orthokeratinizing (and thus are parakeratinizing) but keep the adjective "orthokeratinizing" in the name
for orthokeratinizing odontogenic keratocysts. Currently, "odontogenic keratocyst" without other
modifiers implies one that is parakeratinizing and thus aggressive.
It should be remembered that odontogenic keratocysts are part of the basal cell-nevus syndrome, an
autosomal dominant condition with high penetrance and variable expressivity. Any patient that presents
with multiple (more than one) keratocysts should be evaluated for this syndrome.
Odontogenic keratocysts are treated by enucleation and curettage followed by chemical cautery or
peripheral ostectomy. These patients should be followed for 10 years following removal of the cyst with
a panoramic radiograph every year for 5 years and then every other year.
A 21 year old female presented with asymptomatic buccal cortical plate expansion in the
mandibular left posterior region. A radiograph showed a radiolucency extending from the mandibular left
second premolar to the third molar region.
Unicystic ameloblastoma is a variant of ameloblastoma. It is one of the most difficult
of the odontogenic lesions to diagnose. Clinically it may be asymptomatic or may expand the cortical
plate and may resorbe the tooth structure. Radiographically it presents as a unilocular radiolucency.
Microscopically it shows a palisaded basal layer, polarization of basal cell nuclei to the end of the
cells, hyperchromatism of the basal cells, vacuolation of the basal cell cytoplasm, stratum spinosum like
stellate reticulum and sometimes keratinization. Portions of unicystic ameloblastoma do not show
ameloblastic epithelium and secondary inflammation make the diagnosis very difficult. Importantly,
ameloblastic epithelium must not penetrate the wall of the cyst. If so, the lesion behaves as a solid
ameloblastoma. Microscopic variants include luminal type in which the ameloblastic epithelium is
confined to the luminal layer and the intraluminal in which nodules of ameloblastic epithelium project
into the cyst lumen.
These lesions are destructive and 15% may recur after simple enucleation.
Figure 4 illustrates the histopathology of three different types of cysts discussed so far, unicystic
ameloblastoma, dentigerous cyst and odontogenic keratocyst.
Case 3 - Figure 3 - Unicystic ameloblastoma
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Case 3 - Figure 4 - Comparison of unicystic ameloblastoma (top), dentigerous cyst (middle) and odontogenic keratocyst (bottom)
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A 62 year old female has a firm mildly painful swelling in the buccal vestibule adjacent to
the mandibular right first premolar and canine. Radiographs show a 1.5 cm radiolucency distal to the
root of the canine involving the apex of the premolar.
Ameloblastoma is a neoplasm that recapitulates ameloblastic development. There are
three clinical types, solid, unicystic (discussed as Case 3) and peripheral. Solid ameloblastoma
involves the mandible in 80% of cases and the maxilla in 20%. The male:female incidence is equal and the
median age is 35. Radiographically the lesion may be unilocular or multilocular and the appearance has
been described as being soap bubble or honeycomb like. There are many variants of solid ameloblastoma:
follicular, acanthomatous, desmoplastic, basal cell, plexiform and granular cell. Follicular variants
are the most common and show epithelial islands (Figures 2,3) with peripheral columnar cells with reverse
polarity and whose central areas resemble stellate reticulum. Cyst formation is common and the stroma
may be fibrous. The acanthomatous variant (Figure 4) shows abundant keratin formation and should not be
mistaken for squamous cell carcinoma. The desmoplastic variant shows small epithelial nests and cords
with dense fibrous stroma. There are few peripheral palisaded cells and the centrally placed cells are
less spindled. The basal cell variant is least common and peripheral columnar cells can be lacking and
there may be little stellate reticulum present. The plexiform variant shows long anastomosing plexiform
epithelial cords. The granular cell variant shows cells whose cytoplasm is granular and the change may
be focal or widespread. No matter what the variant, the behavior is the same. Ameloblastoma infiltrates
cancellous bone such that a 1 centimeter margin beyond the radiographic extent of the tumor is suggested
for surgical therapy.
A 7 year old male presents with expansion of the mandible distal to the left first primary
molar. The radiographs reveal a well circumscribed radiolucency coronally to an impacted molar.
Ameloblastic fibroma is a proliferation of immature odontogenic mesenchymal and
epithelial cells. No mineralization or production of enamel, dentin or cementum is seen. There is no
gender predilection and most patients are under 20 years of age. It may occur in any tooth bearing site
but is more common in the premolar-molar region of the mandible. Radiographically they are well
demarcated, well corticated radiolucencies that may be unilocular or multilocular.
Microscopically they are composed of young basophilic fibromyxoid tissue. There are islands, cords
and strands of ovoid, cuboidal and occasionally columnar epithelium. There is no evidence of
mineralization.
Treatment is conservative surgical enucleation and the recurrence rates are very low.
A 57 year old female presents with a 3 cm enlargement of the left mandibular ramus. The
radiograph reveals a well demarcated, mixed radiolucency/radio-opacity.
Calcifying odontogenic cyst may vary from a simple central bony, thin epithelial lined
cyst to a complex focally solid tumor-like mass. Some believe that variants may be a neoplasm with
cystic degeneration. They may occur in any tooth bearing site but most often in the posterior mandible.
There is no gender predilection and the lesion has been diagnosed in patients under 10 and over 80.
Clinically they may present as a firm but asymptomatic expansion of the buccal cortical plate.
Radiographically they may be unilocular or multilocular. Varying amounts of radio-opaque material can be
seen, depending on the amount of mineralization.
Calcifying odontogenic cysts histologically may be cystic, multicystic or solid. They can show a
stratified squamous epithelium with a well defined basal layer consisting of cuboidal or columnar cells.
Ghost cells similar to those found in pilomatricoma are seen. (Figure 3, 4)
In addition mineralization resembling dentin or cementum may be seen.
These lesions are treated with conservative surgical excision and the recurrence rates are very low.
A 50 year old male presents with buccal cortical plate expansion in the right mandibular
premolar region. The second premolar exhibits significant clinical mobility. A radiograph shows a
unilocular circumscribed radiolucency involving the right mandibular premolar region.
Calcifying odontogenic tumor is an epithelial odontogenic tumor characterized by sheets
of hyperchromatic, ovoid and squamous cells with foci of mineralization and amyloid.
They occur more often in the mandible than the maxilla (2:1). They tend to be in the molar and
premolar region and there is a bimodal age pattern, with a slight increase in tumors reported during the
20's and again during the 40's. Radiographically they are well circumscribed corticated, unilocular or
multilocular radiolucencies. Small radio-opacities may be detected.
Microscopically they show island and sheets of polygonal, epithelial cells showing foci of remarkable
pleomorphism and nuclear hyperchromasia. Prominent intracellular bridges are seen and amyloid is
present. Foci of mineralization are seen.
These tumors respond to conservative surgical removal and recurrence rates are less than 10%.
A 27 year old male had swelling of the left maxilla first noticed two weeks previously.
The enlargement was painless. A multilocular radio-opacity involving a signficant portion of the
maxillary sinus was seen.
Odontogenic myxoma is a benign odontogenic neoplasm resembling the mesenchymal portion
of the tooth forming unit, the dental papillae. Clinically they more often occur in the mandible,
generally in the posterior regions, and occur in the second to third decade of life. There is no gender
predilection. They may be unilocular of multilocular on radiographs and have a well demarcated,
corticated border, consistent with their benign histology.
On microscopic examination, myxomas are relatively acellular, with pale basophilic mesenchymal matrix
with prominent thin walled vascular channels. These lesions may contain a variable number of epithelial
rests. The background is composed of spindled or stellate cells with small nuclei. Mitoses are very
rare.
Because of its gelatinous nature, tumor enucleation can be difficult. Enucleation followed by
chemical cauterization is often the therapeutic management of choice for small lesions. Larger lesions
may require resection. Recurrence rates vary significantly based on initial treatment and size of the
lesion at initial diagnosis.
A 27 year old male presents with a well circumscribed radiolucent lesion involving the
impacted maxillary left third molar. The lesion is asymptomatic and of unknown duration.
Glandular odontogenic cyst is most commonly found in the anterior mandible but can be
found in the maxilla as well. Radiographs are not specific and may appear to show a unilocular or
multilocular lesion. The process has well defined margins with a sclerotic border.
Microscopically mucus containing cells in a nonkeratinizing squamous lined cyst are seen. No
stellate retiuculm or uniform basal cell layer is seen. The important microscopic differential diagnosis
includes mucoepidermoid carcinoma. However in glandular odontogenic cyst no large islands of squamous
and mucus cells are seen.
Treatment consists of enucleation and curettage.
A 15 year old female presents with unerupted maxillary left premolars and a well
circumscribed radiolucency noted on the radiograph.
Adenomatoid odontogenic tumors are lesions that are characterized by a female:male
incidence of 2:1, occurrence in the second decade and location in the anterior jaw with a maxilla:
mandible ratio of 2:1. They may be associated with impacted teeth. They are usually a unilocular on
radiographs with a sharp border and may contain fine "snowflake" radio-opacities.
Microscopically they show spindle shape epithelial cells that form rosettes and duct like structures
as well as showing amyloid formation and mineralization.
These lesions are treated conservatively and enucleation may suffice. The recurrence rate is low.
A 13 year old male presents with a well circumscribed radiolucency/radio-opacity of the
left mandibular third molar region.
Ameloblastic fibro-odontomas usually present in young adults in the posterior jaws.
Radiographically they may be unilocular or multilocular but are well circumscribed with a corticated
border with a mixed radiolucency/radio-opacity appearance.
Microscopically there are island and cords of cuboidal epithelium in a myxoid background.
Mineralization is seen with enamel, dentin and cementum formation. The mineralized material may be
organized to resemble poorly formed teeth.
These lesions are treated conservatively with simple curettage and recurrences are rare.
A 24 year old male presents with an asymptomatic multilocular, radio-opaque lesion in the
maxillary premolar region of unknown duration. The lesion has caused dilaceration of the first premolar
roots.
Odontomas are the most common odontogenic tumor. Some believe that these lesions are
actually hamartomas. The maxilla is more often involved than the mandible. Most cases are diagnosed
before age 20. Odontomas are either classified as compound or complex. Radiographically a homogeneous
radio-opacity is a complex odontoma and a lobulated radio-opacity is likely to be compound odontoma.
Grossly and microscopically, compound odontomas are arranged to suggest teeth while complex odontomas
show sheets of dentin, cementum and enamel epithelium arranged haphazardly.
The treatment of odontoma is simple curettage and these lesions have no recurrence.
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