Keywords
ameloblastoma - cone beam computed tomography - exophytic - plexiform
Introduction
Three-dimensional imaging (3D) in the field of dentistry was evolved to meet the demands
of advanced technologies in diagnosis and also to decide upon various treatment strategies
that pose both diagnostic and surgical challenges. Cone-beam computed tomography (CBCT)
with its copious applications is a more convincing diagnostic tool as this imaging
modality eliminates limitations of two-dimensional (2D) radiography such as superimpositions,
distortions, etc.[1] CBCT can visualize the outline of the skin and also the mucosal outline of the pharynx
and oral cavity though lacks soft tissue contrast resolution. It allows clinicians
to view and appreciate the lesion in three-dimensional architecture thoroughly than
plain radiographs such as panoramic, lateral cephalometric, and anterior–posterior
projections.[2] CBCT can provide a detailed examination of hard tissue findings. CBCT may especially
be useful in distinguishing the desmoplastic subtype of ameloblastoma from other types
as it contains coarse internal calcifications as well as the destruction of surrounding
cortices.
Ameloblastoma is a tumor of benign, but aggressive nature of odontogenic origin. Robinson
in 1937, defined ameloblastoma as “usually unicentric, nonfunctional, intermittent
in growth, anatomically benign, and clinically persistent.” According to the update
from the 4th edition of the World Health Organization Classification of Head and Neck Tumors on
Odontogenic and Maxillofacial Bone Tumors in 2017, ameloblastomas are classified under
benign odontogenic tumors of epithelial origin, and the classification has been simplified
and narrowed to ameloblastoma, unicystic ameloblastoma, and extraosseous/peripheral
types.[3] The involvement of mucosa in solid intraosseous ameloblastoma is a rare secondary
phenomenon, and if it occurs, it is often confused with peripheral exophytic lesions
such as peripheral giant cell granuloma and peripheral ossifying fibroma. Kuru[4] in 1911, first reported the case of intraosseous ameloblastoma manifesting as a
peripheral exophytic lesion. Intraosseous ameloblastoma originates from a central
lesion of the jawbone, proliferates locally, and may infiltrate the cancellous marrow
spaces expanding the bone rather than perforating it. But very rarely, the central
type of ameloblastoma may tend to perforate the cortex of the bone to penetrate and
present as extraosseous exophytic growth of the gingiva or over the adjacent alveolar
mucosa. This article discusses such a rare and abovementioned unusual clinical presentation,
which probably to the best of our knowledge would be the eighth reported case in the
literature. Informed consent for the images or other clinical information relating
to this case was obtained from the patient.
Case History
A 23-year-old male patient reported to the Department of Oral Medicine and Radiology
with a chief complaint of swelling in the right lower back teeth gum region for 2
and a half months. The patient had noticed the swelling 2 and a half months back which
was initially small in size and gradually increased to the presented size. The swelling
was not associated with pain, numbness, or paraesthesia, and there was no history
of trauma. There were no harmful habits in his personal history. All vitals were within
normal limits. On extraoral examination, there was a mild facial asymmetry with a
diffuse swelling on the right lower third of the face, which was measuring approximately
3 × 4 cm in size. The overlying skin appeared normal with no visible pulsations and
no secondary surface changes such as sinus opening or pus discharge. On palpation,
the swelling was firm in consistency and nontender with no local rise in temperature,
and it was nonfluctuant, nonpulsatile, noncompressible, and nonreducible ([Fig. 1]). Two right submandibular lymph nodes of size roughly measuring less than 0.5 cm
were enlarged, oval in shape, firm in consistency, mobile, and nontender.
Fig. 1 Extraoral view showing mild facial asymmetry.
On intraoral examination, a proliferative sessile exophytic growth of size approximately
4 × 1 cm, was present in the buccal aspect of the marginal gingiva of 45, 46, and
47, red in color with the lobulated surface. The growth is firm and nontender with
no visible pus discharge or bleeding ([Fig. 2]). There was evidence of bicortical expansion from 44 to 47 with obliteration of
the buccal vestibule from 45 to 47 ([Fig. 3]).
Fig. 2 Intraoral view showing the exophytic gingival growth.
Fig. 3 Bicortical expansion with a displacement of 46.
Grade III mobility was elicited in 45, 46, and 47 with a displacement of the crown
of 45, 46 from normal alignment ([Fig. 3]). The oral hygiene status was fair. On the basis of history and clinical examination,
we inferred a provisional diagnosis of peripheral exophytic growth most probably pyogenic
granuloma. However, an exophytic growth would not cause bicortical expansion or grade
III mobility and displacement of adjacent teeth, which made this case arrive into
a clinical dilemma with a suspicion to think in terms of malignancy such as squamous
cell carcinoma or osteosarcoma. Considering the location and severity, ameloblastoma
and central giant cell granuloma were considered in the differential diagnosis.
Investigations
Routine hematological investigations revealed no significant findings and were within
normal limits.
Orthopantomogram revealed a well-defined unilocular radiolucency extending from mesial
of 44 to distal of 47 with an evidence of knife-edge type of root resorption in 44,
45, and 47 and complete root resorption up to the cervical third of crown in 46 with
scalloped corticated borders in the inferior aspect along the inferior border of the
mandible and right mandibular nerve canal displaced downward ([Fig. 4]).
Fig. 4 Panoramic view: well-defined unilocular lesion with corticated borders and resorption
of roots.
The mandibular right lateral occlusal view revealed significant expansion of the buccal
cortex which was less pronounced on the lingual aspect ([Fig. 5]).
Fig. 5 Lateral mandibular occlusal view: bicortical expansion without perforation of cortex.
CBCT axial section revealed a well-defined multilocular hypodense region extending
from distal of 43 to distal of 47 with evidence of buccal and lingual cortical plate
expansion and thinning with perforation on a buccal plate in 44 and 47 regions ([Fig. 6A]). The axial section also showed a single, straight, complete, and thick septa at
the level of the middle third of the root of 44 ([Fig. 6B]) that was recognized to separate the tumor into large and small compartments, anterior
and posterior to 44. Coronal section showed loss of superior boundary of right inferior
alveolar nerve canal with knife-edge type root resorption in 44, 45, and 47. There
was complete root resorption extending up to the cervical third of the crown in 46
([Fig. 6C]). The sagittal section revealed tilting of the crown of 46 to distal aspect ([Fig. 6D]). The 3D reconstruction revealed through and through perforation of the buccal and
lingual cortical plates with the intact inferior border of the mandible ([Fig. 6E]).
Fig. 6 (A) CBCT axial view showing a well-defined multilocular hypodense lesion with bicortical
expansion and perforation of the buccal cortex marked in green arrows. (B) CBCT axial view showing single, straight, complete, and thick septa marked in green
arrow. (C) CBCT coronal view showing perforation of cortex with resorption of root of 46 marked
in green arrows. (D) CBCT sagittal view showing periapical hypodense lesion with tilting of 46 to the
distal aspect marked in green arrow (E). CBCT 3D reconstruction view showing through and through the perforation of buccal
and lingual cortex. CBCT, cone beam computed tomography.
H & E-stained section from an incisional biopsy of the intraoral exophytic growth
exhibited network of odontogenic epithelium forming a plexiform pattern and reverse
polarity of peripheral cells with extensive inflammatory reaction suggesting a plexiform
type of ameloblastoma with dysplastic features. However, excisional biopsy sections
from the noninflammatory area were advised for the final diagnosis. The lesion was
surgically enucleated with curettage and extraction of the involved teeth 42, 43,
44, 45, 46, 47, and 48 ([Fig. 7]) under general anesthesia.
Fig. 7 Gross view of surgically enucleated and curetted lesion with the extraction of involved
teeth.
H & E-stained section from excisional biopsy exhibited a network of the odontogenic
epithelium with clear distinction of peripheral and central cells. The peripheral
cells showed reversal of polarity in occasional areas, and the central cells of the
network showed a stellate type of cells with areas of cystic degeneration in the connective
tissue stromal area ([Fig. 8]). The histopathology of the lesion was confirmative of “plexiform type of ameloblastoma.”
The patient was followed up after marginal mandibulectomy of the involved lesional
site. Immediate short-term follow-up after 1 week from the day of surgery showed satisfactorily
healing surgical site with a complaint of numbness of the lower lip, which was probably
due to iatrogenic injury to the mandibular nerve. Later after 4 months, long-term
follow-up revealed a completely healed surgical site ([Fig. 9]) with reversal of lost sensations to the lower lip. The patient will be further
planned for prosthetic rehabilitation of the surgical defect and missing teeth so
as to improve his masticatory function.
Fig. 8 H- and E-stained section exhibiting plexiform ameloblastoma.
Fig. 9 Long-term follow-up showing completely healed surgical defect with missing teeth
42 to 48.
Discussion
Ameloblastoma is a slow growing, locally aggressive, and benign epithelial odontogenic
tumor, which accounts for 10% of all odontogenic tumors in the jaw. This conventional
type is particularly seen in young adults with a median age of 35 years with no specific
gender predilection. About 80% of these cases occur in the mandible frequently in
the posterior region.[5] Histologically, it displays two distinct types: follicular and plexiform. In the
plexiform ameloblastoma, the ameloblast-like tumor cells are arranged in irregular
masses, or as a network of interconnecting strands of cells and sometimes double rows
of columnar cells are lined up back-to-back.[6]
The existence of peripheral (soft tissue location) forms of ameloblastoma is well
documented though rare. However, ameloblastoma exhibiting as soft tissue gingival
overgrowth is a rare phenomenon. Kuru[4] in 1911, reported the first case of intraosseous ameloblastoma manifesting as a
peripheral (exophytic) lesion. Later, two similar cases were reported by Tongdee and
Ganggakavin and Stevenson and Austin respectively, probably very few similar cases
have been reported in the English literature.[7] CBCT imaging is highly useful in revealing regions of perforation of the expanded
cortical plate as a result of the inability of the production of periosteal new bone
to keep up with the rate of growth of the expanding ameloblastoma.
In our case, most of the clinical features were favorable for the diagnosis of peripheral
exophytic lesions such as pyogenic granuloma or peripheral giant cell granuloma.
However, effects on surrounding structures such as tooth mobility, displacement, and
cortical expansions are uncommon with these exophytic lesions, which enunciated a
clinical dilemma in this case. There were no carious teeth in the involved region
to think in terms of radicular cyst nor was there any missing tooth in that quadrant
to consider dentigerous cyst. An odontogenic keratocyst does not expand the bone to
this degree, and hence the mere consideration of malignancies such as squamous cell
carcinoma or osteosarcoma could not be ruled out. A radiological dilemma arose after
the orthopantomogram, which revealed a well-defined unilocular radiolucency with sclerotic
borders suggestive of cystic lesions with significant root resorption thereby ruling
out malignancy. Bicortical expansion with thinning of the buccal plate without perforation
was seen in the lateral occlusal view. To have an unambiguous radiographical finding
and also to ratify whether the peripheral exophytic growth is an independent lesion
or extension from the central lesion within the bone, CBCT was recommended.
CBCT unveiled the multilocularity of the lesion with breaching of the buccal cortical
plate causing perforation through which the lesion had proliferated as an exophytic
growth over the gingiva. Further, Hounsfield units (HU) derived from greyscale values
of CBCT, traced few areas of cyst-like component (3.9 to 22.9 HU) and major areas
with tumor components (35.9 plus/minus 12.6 HU) which clearly depicted that the lesion
would probably be the result of cystic degeneration which was later confirmed in the
histopathological report.[8]
[9] This finally convinced the diagnosis of an intraosseous odontogenic tumor masquerading
with a peripheral exophytic growth, proved in the histopathological sections as plexiform
ameloblastoma. Sanjay et al[7] reported a similar case in a 45-year-old male patient in the same location. Kiran
Holikatti et al[10] and Tabatabaei et al[11] reported ameloblastomas presenting as gingival enlargement with an unusual presentation
in 50-year-old female and 41-year-old female patients, respectively, at the third
molar region. But in all three of the abovementioned cases, routine 2D imaging itself
depicted multilocular radiolucency (soap bubble appearance) although there was no
bicortical expansion and clued the diagnosis in favor of odontogenic cyst or tumor,
which was clinically well relatable without posing clinical or radiodiagnostic dilemma.
However, unilocular radiolucency with buccal cortex expansion mimicking our case was
reported by Shetty et al[12] as central plexiform ameloblastoma with exophytic growth, but in the anterior mandible
in a 11-year-old patient. A complete review of all the seven cases reported so far
in the literature along with the present case with all details is represented in the
table below ([Table 1]).
Table 1
Detailed comparison of seven reported cases from the literature
|
Author and Year
|
Age
|
Sex
|
Site and size
|
Radiological features
|
Histopathological features
|
|
Kuru 1911[a]
|
–
|
–
|
–
|
–
|
|
|
Tongdee and Ganggakavin, 1978[a]
|
–
|
–
|
–
|
–
|
–
|
|
Stevenson and Austin, 1990
|
47 y
|
Female
|
Left mandibular third molar alveolar crest region, approximately 1 cm in size.
|
Intraoral periapical radiograph showed well-defined unilocular radiolucency.
|
Follicular and acanthomatous types
|
|
Shetty et al, 2010
|
11 y
|
Male
|
Left mandibular anterior region, of size 3 cm.
|
The panoramic view showed large unilocular radiolucency.
|
Plexiform type
|
|
Sanjay et al, 2011
|
45 y
|
Male
|
Right anterior region of the mandible of size 3.5 × 3.5 cm.
|
The intraoral periapical radiograph showed a multilocular soap bubble appearance.
|
Follicular type
|
|
Holikatti et al, 2015
|
50 y
|
Female
|
The lingual aspect of the right posterior mandibular alveolar ridge region, approximately
3 × 3 cm in size.
|
The panoramic view revealed irregular multilocular radiolucency.
|
Acanthomatous type
|
|
Tabatabaei et al, 2014
|
41 y
|
Female
|
Posterior region of the right third molar tooth of size 3 × 3.5 cm.
|
The panoramic view revealed soap bubble multilocular radiolucency with well-defined
margins.
|
Follicular type
|
|
The Present case report
|
23 y
|
Male
|
Right mandibular premolar, a molar region of size 4 × 1 cm.
|
The panoramic view showed well-defined unilocular radiolucency.
CBCT showed well-defined multilocular hypodense lesion.
|
Plexiform type
|
a Detailed information is not available in the literature.
Although peripheral ameloblastoma and peripheral intraosseous ameloblastoma exhibit
similar clinicopathological features presenting as an exophytic soft-tissue lesion,
the difference in their biological behavior often challenges diagnosis.[13] This is where CBCT plays a pivotal role in clearly demarcating the penetration of
intraosseous tumor from inside by perforating the buccal cortical plate thus eliminating
peripheral ameloblastoma, which is completely superficial and seldom causes bone infiltration,
even before confirming it through histopathological criteria.
This presented case is rare in literature because of the age that it was seen in a
young patient (23 years old) and the ability of the lesion to penetrate the periosteum
and breach through the overlying epithelium presenting into an unusual prominent exophytic
growth thus exhibiting a diagnostic challenge both clinically and radiographically.
To conclude, the presentation of such tumors with an exophytic lesion could always
be a diagnostic challenge and would invite all possible confusions to consider the
most common exophytic lesions and the rare peripheral ameloblastoma. Thus, CBCT provides
all accessory information when compared with conventional panoramic radiography about
the extent, borders, internal architecture of the bone, the effects imposed on adjacent
structures, being a highly useful tool with easy availability and less cost for accurate
diagnosis of lesions of the jaws, especially to counteract such clinical dilemma by
allowing the clinicians to better evaluate for best treatment outcomes.
