Keywords
Ameloblastoma - granular - stellate reticulum
Introduction
Odontogenic tumors (OT) are a collection of heterogeneous lesions derived from epithelial
and/or mesenchymal elements that are part of the tooth-forming apparatus.[[1]] Ameloblastoma is well-documented as a locally invasive benign neoplasm thought
to ascend from the cellular components of the enamel organ.[[2]] An epithelial odontogenic tumor of the jaw that exhibits diverse microscopic patterns,
which occurs either individually or in combination with other patterns.[[3]] The current World Health Organization (WHO2017) classification of odontogenic tumors
divides ameloblastoma into four types as follows: ameloblastoma, unicystic type, ameloblastoma
extraosseous or peripheral type, and metastasizing malignant.[[4]] Ameloblastoma most significantly concerns oral pathologists due to its high incidence
among all odontogenic tumors and true neoplastic (infiltrative and recurrent) potential
combined with its varieties of histopathological patterns.[[5]] The six main histopathological subtypes (variants) of ameloblastoma are as follows:
(a) follicular, (b) plexiform, (c) acanthomatous, (d) granular cells, (e) basal cell,
and (f) desmoplastic form.[[6]]
It is generally a painless, slow growing, locally aggressive tumor causing expansion
of the cortical bone, perforation of the lingual or the buccal cortical plate and
infiltration of the soft tissues. It has peak incidence in the third and fourth decade
of life, but can be found in any age group with equal gender predilection (1:1). In
the mandible, majority of ameloblastomas are found in the molar ramus region.[[7]] Granular cell ameloblastoma is one of the rarest entities and accounts for about
5% of all ameloblastomas.[[8]] Histopathologically, it is characterized by having numerous large eosinophilic
granular cells.[[9]]
Case Report
A 35-year-old female patient visited the department of Oral Medicine and Radiology
with a chief complaint of swelling in the right side of the face for the past 6 months.
Patient was apparently normal one year ago. Then she noticed swelling in the right
side of the face for which she consulted a dentist and got two teeth extracted from
the right lower back tooth region. She gave a history that the swelling was subsided.
Again, after 6 months she started to notice the swelling started in the same region,
which was initially smaller in size and gradually increased to the present size. There
was no history of pain associated with the swelling.
On extra oral examination, diffuse swelling was present on right side of the face
measuring about 3 × 5 cm extending anteroposteriorly from the corner of the lip to
the angle of the mandible and superoinferiorly from corner of the lip to 2 cm below
the inferior border of the mandible [[Figure 1]]. Skin over the swelling was stretched and shiny. No ulcerations or discharge was
present. Facial asymmetry was present on the Right side. On palpation, the swelling
was hard in consistency and non-tender. Skin over the swelling was pinchable. Mouth
opening was not restricted. Lymph node examination revealed two submandibular glands,
which were palpable, both measuring 1 cm in diameter, firm in consistency, tender,
and freely movable on the right side.
Figure 1: Extra oral view
On intraoral examination, diffuse swelling involving the right lower alveolus extending
from mesial aspect of 45 to retromolar trigone. There was obliteration of the buccal
vestibule. Swelling was present on the lingual aspect extending to 1 cm above the
floor of the mouth. The surface over the posterior aspect was erythematous and covered
by white slough area [[Figure 2]]. No pus discharge or bleeding was present. On palpation, the swelling was soft
to hard in consistency. Buccal and lingual cortical plate expansion was present. Provisionally
diagnosed as benign tumor of the right mandible. Investigations carried out were panoramic
radiography [[Figure 3]], computed tomography [[Figure 4]], blood investigations, and excisional biopsy. Panoramic Radiograph revealed a multilocular
lesion in the right body of the mandible extending from the distal aspect of 43 extending
to the right ramus of the mandible. There was destruction of inferior border and posterior
border of ramus. Inferior alveolar canal was not appreciated. There was absence of
resorption of roots 44, 45, 46. Computed tomography axial slice revealed diffuse expansile
lesion in right side of the mandible with soft tissue enlargement of the same side.
There was involvement of right angle and ramus of mandible with buccal and cortical
plate destruction. 3D CT revealed the involvement of the right body, angle, and ramus
of the mandible with bicortical plate expansion. Excisional biopsy was done [[Figure 5]] and specimen [[Figure 6]] was sent for histopathological examination, which revealed granular cell ameloblastoma
of the right mandible [[Figure 7]].
Figure 2: Intraoral view
Figure 3: Panoramic radiograph reveals multilocular radiolucency in the right body and ramus
of mandible with thinning of the inferior border of mandible and break in the ramus
Figure 4: Axial CT scan showing a well-defined multilocular lesion in right side of mandible
with bicortical expansion and multiple perforations. 3D CT showing a large destructive
lesion of mandible extending from right first molar to ramus of the right mandible
Figure 5: Surgical view
Figure 6: Biopsy Specimen
Figure 7: Photomicrograph
Discussion
Churchill in 1934, defined ameloblastoma as unicentric, non functional, intermittently
growing anatomically benign but clinically persistent tumor.[[10]] Granular cell change in ameloblastoma was first reported by Krompecher in 1918
and was called pseudoxanthomatous cells.[[11]] Granular cell ameloblastoma is an uncommon variant of ameloblastoma. Kameyama et al. stated in their clinico pathological study that only 1 out of 77 ameloblastoma cases
was classified as Granular cell ameloblastoma.[[12]] Reichart et al. studied all accessible literature on ameloblastoma of the jaws from 1960 to 1993
and reported that out of a total of 1593 cases with available data on histologic subtypes,
there were only 56 cases of the granular cell variant.[[13]]
The biological behavior of granular cell ameloblastoma does not seem to fluctuate
from the other histologic subtypes of ameloblastoma; it can be locally aggressive
and has a comparatively greater chance of recurrence.[[14]] Granular cell ameloblastoma is analyzed by the presence of granular cells, which
characteristically occur within the central area of tumor and progressively replace
the stellate reticulum.[[15]] The granular cells have an oval to polyhedral shape and tend to be large. The follicles
may have a thin rim of stellate reticulum like cells that separates the granular cells
from the peripheral columnar layer and the nucleus is displaced to the periphery of
the cells. Conspicuous coarse granules pack and distend the cytoplasm and have a tendency
to stain eosin, granting a notable manifestation. Occasionally, granular cell change
may affect the peripheral columnar cells.[[16]] Ultrastructurally, the granular cells are consistent with lysosomes and are immunohistochemically
positive for vimentin, CD68, muramidase, and bcl-2 and negative for cytokeratin and
S-100 protein.[[17]]
Radiographically granular cell ameloblastoma resembles all the classical features
of ameloblastoma. The most typical radiographic feature is that of a multilocular
radiolucent lesion. The lesion is often described as having a “soap bubble” appearance
(when the radiolucent loculations are large) or as being “honeycombed” (when the loculations
are small). Buccal and lingual cortical expansion is frequently present. Resorption
of the roots of teeth adjacent to the tumor is common. All the classical radiographic
features were noted in our case except for root resorption. In many cases an unerupted
tooth, most often a mandibular third molar is associated with the radiolucent defect.[[18]]
The granular cell tumor is an unusual benign soft tissue neoplasm that displays predilection
for the oral cavity. The most common site is the tongue, followed by the buccal mucosa.
Differential diagnosis from a granular cell ameloblastoma is necessary when there
is peripheral localization or cortical perforation and soft tissue extension of the
ameloblastoma. Granular cell tumor usually occurs in the fourth to sixth decades and
shows a female predilection. Clinically, it appears as an asymptomatic sessile nodule
of small size.[[18]]
Conclusion
Granular cell ameloblastoma is one of the rarest variant of ameloblastoma with unique
and higher recurrence rate. However, it should be differentiated from the other granular
cell lesions primarily because of its aggressiveness and higher recurrence rate. Patient
has to be periodically reviewed because of its high recurrence rate.
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