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the peripheral ameloblastoma ( pa ) is generally described as an exceedingly rare lesion , which accounts for 15% of all ameloblastomas .
the pa is also known as the extra - osseous ameloblastoma , soft tissue ameloblastoma , ameloblastoma of mucosal origin , or ameloblastoma of the gingiva .
pa shows several histologic characteristics of an intra - osseous , infiltrating ameloblastoma ( ia ) but it occurs in soft tissues overlying and does not invade the underlying bone .
a 44-year - old male patient presented to the department of oral pathology and microbiology with a firm soft - tissue lesion behind the maxillary right third molar .
the patient has been aware of the lesion since last 1-year and the lesion was gradually increasing in size .
there was no extraoral swelling on the right side of face or associated lymph node enlargement .
on palpation , a firm submucosal mass was revealed posterior to maxillary right third molar of approximately 2 cm  2 cm in size .
lesion was spherical in shape and not fixed to the underlying structures [ figure 1 ] .
intraoral view of 2  2 cm lesion in right retromolar trigone area intraoral periapical showed no evidence of any bone involvement .
magnetic resonance images report revealed a well - defined lesion of 1.8 cm  1.6 cm in the right retromolar trigone with no obvious erosion of bony surface .
it appears as hypointense signal t1-weighted image [ figure 2a ] , and hyperintense signal on short tau inversion recovery image [ figure 2b ] . on suspecting a benign soft tissue tumor of salivary gland , a peripheral odontogenic tumor or a tumor like - growth
( a ) mri shows a well - defined lesion of 1.8  1.6 cm in the right retromolar trigone .
t1 weighted image showing hypointense signal . ( b ) lesion appear as hyperintense signal on stir ( short ti inversion recovery ) image h and e stained sections showed dense connective tissue stroma containing numerous islands and cords of odontogenic epithelium [ figure 3 ] .
peripheral cell were tall columnar / cuboidal , palisaded , and polarized with stellate - like cells present in the center of the islands showing squamous metaplasia
. islands of odontogenic epithelium showing microcysts and central stellate reticulum - like cells with squamous metaplasia ( h and e stain , 10 ) the histologic findings were suggestive of peripheral acanthomatous ameloblastoma . to further confirm the diagnosis , immunohistochemical analysis was done using ck19 and ber - ep4 markers [ figure 4 ] .
lesional areas showed strong positive expression for ck19 while negative expression for ber - ep4 .
( a ) lesional tissue showing strongly positive expression for ck19 ( 10 ) ( b ) lesional tissue showing negative expression for ber - ep4 ( 10 )
pa can be confused clinically with an epulis , fibroma , gingival tumor , or carcinoma including intraoral basal cell carcinoma ( bcc ) and hence difficult to diagnose based only on clinical findings .
similarly in our case , we were not able to suspect pa based only on clinical findings and only after histopathological examination , the final diagnosis was achieved .
bone involvement is noted in only few cases of pa , which has been referred to as cupping or saucerization which results from the pressure of the tumor on bone , while most of the cases of pa are superficial to cortical bone with no sign of bone involvement . in our case ,
pa occurs at a significantly higher age and is more common in males as compared to ia [ table 1 ] .
comparison between pa and ia the most common site for pa is mandibular premolar region ( 32.6% ) followed by anterior mandibular region ( 20.7% ) and maxillary soft palatal tissue of the tuberosity area ( 11.1% ) . in our case ,
, pa has a marked tendency to be acanthomatous as seen in our case . regarding the cellular origin of pa ,
first , lesions which are located entirely within the connective tissue of the gingiva , showing no continuity with the surface epithelium , most likely arise from remnants of the dental lamina located in the soft tissues overlying the tooth - bearing areas of the jaw bones .
second , lesions may arise from the surface epithelium , in some cases at one or a few sites and in others multifocally . in the present case , as there was no continuity of the lesional tissue with the surface epithelium , hence it appears to arise from the remnants of the dental lamina .
immunohistochemical profile of pa previous studies have shown that pa and ia are positive for ck19 and negative for ber - ep4 , whereas the opposite is true for bcc . in the study done by kato et al .
, all cases were negative for ber - ep4 , suggesting that pa and ia are tumors with a common origin , and that pa is derived from odontogenic epithelial remnants , rather than from basal cells of the oral epithelium .
thus ihc markers such as ck19 and ber - ep4 can be used to differentiate pa from intraoral bcc . in our case ,
ck19 [ figure 4a ] was expressed strongly positive while ber - ep4 [ figure 4a ] showed negative expression as shown in previous reports .
gardner ( 1977 ) stated that term pa is potentially dangerous in that this diagnosis may lead to unnecessarily aggressive treatment .
the current treatment of choice is conservative supraperiosteal surgical excision with adequate disease - free margins . 
  in the present case ,
the patient denied any form of surgical treatment and hence is kept on regular follow - ups . because of the common perception that pa does not exhibit the persistent growth and invasiveness of ia , it is usually assumed that lesion will not progress after excision .
however , it has been seen that some tumors indeed have significant invasive capacity with high recurrence potential . according to philipsen et al .
( 2001 ) , a total of six cases of a very rare malignant variety of pa have been published .
( 2004 ) reported the first completely documented example of malignant pa with metastasis and they suggested that large size ( over 2 cm in diameter ) is a powerful predictor of aggressive behavior , no matter how apparently innocuous .
immunohistochemical profile of pa previous studies have shown that pa and ia are positive for ck19 and negative for ber - ep4 , whereas the opposite is true for bcc . in the study done by kato et al .
, all cases were negative for ber - ep4 , suggesting that pa and ia are tumors with a common origin , and that pa is derived from odontogenic epithelial remnants , rather than from basal cells of the oral epithelium .
thus ihc markers such as ck19 and ber - ep4 can be used to differentiate pa from intraoral bcc . in our case ,
ck19 [ figure 4a ] was expressed strongly positive while ber - ep4 [ figure 4a ] showed negative expression as shown in previous reports .
gardner ( 1977 ) stated that term pa is potentially dangerous in that this diagnosis may lead to unnecessarily aggressive treatment .
the current treatment of choice is conservative supraperiosteal surgical excision with adequate disease - free margins . 
  in the present case ,
the patient denied any form of surgical treatment and hence is kept on regular follow - ups . because of the common perception that pa does not exhibit the persistent growth and invasiveness of ia , it is usually assumed that lesion will not progress after excision .
however , it has been seen that some tumors indeed have significant invasive capacity with high recurrence potential . according to philipsen et al .
( 2001 ) , a total of six cases of a very rare malignant variety of pa have been published .
( 2004 ) reported the first completely documented example of malignant pa with metastasis and they suggested that large size ( over 2 cm in diameter ) is a powerful predictor of aggressive behavior , no matter how apparently innocuous .
pa is a rare tumor that is histologically identical to ia usually treated by conservative supra - periosteal excision .
long - term follow - up is advised to detect late local recurrences and metastatic transformation .
peripheral ameloblastoma ( pa ) is a rare and unusual entity with histological characteristics similar to those of the common intraosseous ameloblastoma . in this paper , we present a case of pa in a 44-year - old male affecting the right retromolar trigone area along with its immunohistochemical profile using ck19 and ber - ep4 markers .