salivary gland tumors occurring in the sublingual gland are rare as compared to other locations , such as the parotid and submandibular glands . among malignant salivary gland tumors , the most frequent type is adenoid cystic carcinoma , followed by adenocarcinoma and carcinoma ex pleomorphic adenoma .
the malignant component is frequently a poorly differentiated carcinoma , high - grade adenocarcinoma or salivary duct carcinoma .
however , most other types of salivary gland carcinomas have been described in carcinoma ex pleomorphic adenoma , and some cases show diverse differentiation with several distinct types within the tumor mass . according to the world health organization histological classification published in 2005 ,
malignat changes in the pleomorphic adenoma include three different types : carcinoma ex pleomorphic adenoma , carcinosarcoma and metastasizing pleomorphic adenoma .
the macroscopic features that suggest malignant transformation in pleomorphic adenoma include poorly defined and/or infiltrative tumor margins , the presence of foci of hemorrhage , and necrosis .
also the coexistent benign and malignant elements are considered as well . herein , we report a case of carcinoma ex pleomorphic adenoma that occurred in the sublingual gland , and presented histological findings of microinvasion beyond the original capsule and abundant myoepithelial cells .
a 70-year - old japanese man was referred to our clinic for further evaluation of a mass located in the left floor of the mouth .
there were no subjective symptoms , including pain and tenderness , and the patient had not noticed it until his dentist pointed it out .
extraoral examination results were unremarkable and no abnormal mass in the face or lymphadenopathy in the bilateral neck was seen .
an intraoral examination revealed a painless , non - tender , elastic hard , smooth mass measuring 1.5  cm1.5  cm .
the mass was covered by intact oral mucosa and it was not fixed to the surrounding structures , including the mandible ( figure 1 ) .
a reduced secretion of saliva from the left orifice of wharton 's duct was found . in a magnetic resonance ( mr )
examination , a space occupying mass lesion , which showed homogeneous low signal intensity on t1-weighted images and homogeneous intermediate signal intensity on t2-weighted images , was delineated ( figure 2 ) . on dynamic mr images , tumor located in sublingual space
was gradually enhanced as compared to that of surrounding sublingual glands ( figure 3 ) .
the mass was located in the sublingual space and a clear interface with the sublingual gland was evident .
we made a clinical diagnosis of a benign salivary gland tumor originating from the sublingual salivary gland .
since tumors arising from the sublingual gland have a high chance of being malignant , excision of the mass with the sublingual salivary gland in an en bloc fashion via an intraoral approach was performed under general anesthesia . during the operation , the tumor mass was found located deep within the sublingual gland and above the mylohyoid muscle , and a sharp and blunt dissection from the mandible , extrinsic tongue musculature , and mylohyoid muscle was performed .
the postoperative course was uneventful , and there was no recurrence or metastasis for 5 years and 10 months postsurgically .
the macroscopic appearance of the resected specimen was solid in nature and it was completely encapsulated .
the cut surface showed a grayish white , homogeneous , solid mass with no bleeding foci or necrotic areas ( figure 4 ) .
histopathological examination revealed that the tumor was composed of a pleomorphic adenoma consisting of myxoid , chondroid and mucoid materials , as well as duct - like structures and cell - rich mesenchymal tissues ( figure 5a ) .
although it was well encapsulated , there was a rupture of the fibrous capsule and tumor cells had slightly invaded the surrounding fat tissues ( figure 5b ) .
diffuse cell - rich sheets composed of myoepithelial cells with round nuclei were also seen , among which there were mitotic figures and atypical cells ( figure 5c and 5d ) .
immunohistochemical examinations , including smooth muscle actin , s-100 protein and glial fibrillary acidic protein ( gfap ) , cytokeratin were performed . in the parenchyma ,
staining for cytokeratin highlighted the ductal cells , whereas stromal cells that had differentiated into myxoid , chondroid and mucoid cells were not stained .
the cells that composed of cell - rich sheets were positive to smooth muscle actin ( figure 6 ) .
postoperative ultrasound examination of the neck and f - fluorodeoxyglucose positron emission tomography study revealed no metastatic deposits .
based on these findings , a final diagnosis of myoepithelial carcinoma ex pleomorphic adenoma ( pt1n0m0 ) was made .
additional treatments including neck dissection and adjuvant radiation were not performed , because there were no evidences of recurrence and metastasis , and patient adapted a  wait - and - see ' approach .
salivary gland tumors are rarely found located in the sublingual gland , though such masses have been shown to be malignant in 80%90% of the reported cases .
nagler and laufer reported that they did not observe any benign tumors occurring in the sublingual glands .
clinically , an asymptomatic swelling in the floor of the mouth is the most common complaint associated with malignant sublingual gland tumors , though one case was incidentally discovered by a dentist , which was the same as with the present patient , who did not notice the mass until pointed out by his dentist . tumors of the sublingual salivary gland are generally not recognized until they reach an advanced stage , mainly because of minimal symptomatology . in order to detect a sublingual malignant neoplasm in the early stage ,
in addition , it is important to rule out malignancy when a sublingual mass is presented .
a diagnosis of malignant salivary neoplasm must be considered for every patient who has a swelling in the area of the major salivary glands or a submucosal mass in the oral cavity or pharynx , even if the swelling has been present for years . in the present case
, there were no apparent features that indicated a malignant tumor in the results of our physical examination or in diagnostic images .
clinically , we routinely use magnetic resonance imaging ( mri ) as a diagnostic tool for mass lesions located in soft tissues .
reported mr findings for an adenoid cystic carcinoma originating from the sublingual gland and a gingival squamous cell carcinoma that had invaded the sublingual gland , which both demonstrated destruction of the gland . in the present case ,
reported that dynamic mri was useful in differentiating malignant from benign tumors , as well as for detecting the extent of invasion of a sublingual carcinoma . according to the marginal appearance and enhancement timing of the present mass lesion , we considered that it was benign rather than malignant in nature .
further , since a large part of the tumor margin was encapsulated , we thought it was difficult to diagnose the present case as malignant in nature , because of the marginal features on diagnostic images , including those obtained with mri . in the world health organization classification of salivary gland tumors , the histological proportion of benign versus malignant components can be quite variable .
occasionally , extensive sampling is necessary to find the benign component and in rare case , a benign remnant might not be found . as for infiltrative growth ,
three subtypes can be distinguished : non - invasive , minimally invasive and invasive . in the present case ,
our final diagnosis was minimally invasive carcinoma ex pleomorphic adenoma , as there was microinvasion beyond the capsule .
reported a histopathologic subclassification for 37 cases of carcinomas ex pleomorphic adenoma , which yielded 13 cductal , 10 undifferentiated , 9 terminal duct and 3 myoepithelial types , with two cases that could not be classified because of the small csize of the surgical specimen . in the present case , because cells showing myoepithelial differentiation were abundant , it could be subclassified as a myoepithelial type .
tortoledo et al . also reported two variables , measured invasion in millimeters and histological subclassification cof the malignant neoplasm , as valuable guides for prognosis and biologic behavior .
however , they found no definite association between gross dimensions of the tumor and incidence of recurrence or metastasis .
when recurrence and distant metastasis occur , survival is so low ; therefore , early and adequate removal of that carcinoma ex pleomorphic adenoma is extremely critical .
although metastasis to the lung is rare , patients treated for carcinoma ex pleomorphic adenoma should be investigated for distant metastasis , such as to the lungs and bone , thus long term follow - up examinations for local recurrence and systemic metastasis of our patient are essential .
 we report a case of carcinoma ex pleomorphic adenoma of a sublingual gland in a 70-year - old man . under a clinical diagnosis of benign salivary gland tumor , excision of the mass with the sublingual salivary gland in an en bloc fashion via an intraoral approach was performed . 
 histopathologically , there was a rupture of the fibrous capsule and diffuse cell - rich sheets composed of myoepithelial cells with round nuclei were also seen . 
 immunohistochemically , the cells that composed of cell rich sheets were positive to smooth muscle actin . 
 final diagnosis of myoepithelial carcinoma ex pleomorphic adenoma was made . 
Introduction
Case report
Discussion