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CASE REPORT
Year : 2019  |  Volume : 8  |  Issue : 4  |  Page : 268-271

Pleomorphic adenoma of soft palate with extensive squamous metaplasia – A diagnostic enigma


1 Department of Pathology, Institute of Medical Sciences and SUM Hospital, Bhubaneswar, Odisha, India
2 Department of E.N.T, Institute of Medical Sciences and SUM Hospital, Bhubaneswar, Odisha, India
3 Department of Radiology, Institute of Medical Sciences and SUM Hospital, Bhubaneswar, Odisha, India
4 Department of Surgical Oncology, Institute of Medical Sciences and SUM Hospital, Bhubaneswar, Odisha, India

Date of Submission07-Nov-2018
Date of Decision22-Aug-2019
Date of Acceptance28-Sep-2019
Date of Web Publication16-Dec-2019

Correspondence Address:
Prof. Rashmi Patnayak
Department of Pathology, Institute of Medical Sciences and SUM Hospital, Bhubaneswar, Odisha
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JDRNTRUHS.JDRNTRUHS_103_18

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  Abstract 


Pleomorphic adenoma is the most common salivary gland tumor. It can have a wide range of morphological spectrum. But extensive squamous metaplasia mimicking squamous cell carcinoma is quite uncommon. Palate is a common site for minor salivary gland tumor. Less than hundred cases of pleomorphic adenoma with extensive squamous metaplasia have been reported in English literature, thus making it a rare entity. A 60-year old female presented with a well-defined swelling in the soft palate. The histology was reported as pleomorphic adenoma of soft palate with extensive squamous metaplasia and focal adipocytic metaplasia. The histopathological identification of this entity is important as it can mimic malignancy, particularly squamous cell carcinoma. Correct diagnosis helps in unnecessary aggressive therapy.

Keywords: Minor salivary gland tumor, pleomorphic adenoma, soft palate, squamous metaplasia


How to cite this article:
Patnayak R, Mohanty S, Sahoo AK, Panda AK, Jena A. Pleomorphic adenoma of soft palate with extensive squamous metaplasia – A diagnostic enigma. J NTR Univ Health Sci 2019;8:268-71

How to cite this URL:
Patnayak R, Mohanty S, Sahoo AK, Panda AK, Jena A. Pleomorphic adenoma of soft palate with extensive squamous metaplasia – A diagnostic enigma. J NTR Univ Health Sci [serial online] 2019 [cited 2020 Apr 7];8:268-71. Available from: http://www.jdrntruhs.org/text.asp?2019/8/4/268/273129




  Introduction Top


Pleomorphic adenoma is the most common benign salivary gland tumor. It accounts for a majority of all salivary gland neoplasms.[1],[2] The incidence of pleomorphic adenoma in intraoral minor salivary glands is 40%–50%.[2],[3] The morphological patterns has wide variations including presence of squamous cells, mucous cells, oncocytes, sebaceous cells, bone, adipose tissue, and crystalline materials.[1],[2],[3] There are several unusual histological findings in pleomorphic adenoma that may mimic malignancy, like extensive squamous metaplasia mimicking squamous cell carcinoma (SCC). This can be a source of potential diagnostic pitfall.[4] Focal squamous metaplasia is found in about 20% of pleomorphic adenoma.[2],[3],[5] This squamous metaplasia is attributed to ischemia, repair following infarction, and necrosis of the salivary gland. Rarely extensive squamous metaplasia with cystic changes is reported.[2],[3],[4] Here, we present an unusual case of pleomorphic adenoma of soft palate with extensive squamous metaplasia and focal adipocytic metaplasia.


  Case Report Top


A 60-year-old female presented with a swelling in the soft palate of 2 months duration. The swelling was painless. She did not have any other complaint. The swelling was well-defined and of the size 2 × 2 cm. Clinically, the swelling was diagnosed as benign cyst of salivary gland origin. Her computed tomography picture showed a well-defined swelling in the soft palate [Figure 1]a, [Figure 1]b. She underwent complete exicisional biopsy. The cut section of the gross specimen was grayish white and a well-defined solid mass was noted. There were no cystic areas, hemorrhage, or necrosis [Figure 1]c. Histopathological sections revealed stratified squamous lining epithelium and a well-defined lesion in the subepithelium. There were islands and nests of squamous cells with many keratin pearls constituting about 80% of the tumor. The cells had bland nuclear morphology and mitotic activity was minimal. Focal ductal and myoepithelial proliferation was noted. A small chondromyxoid area was seen. There were no areas of necrosis. Capsular or vascular invasion was not seen. Focal adipocytic metaplasia is also noted. Adjacent benign minor salivary gland was present [Figure 1]d, [Figure 1]e, [Figure 1]f, [Figure 1]g,[Figure 1]h. The final histopathology diagnosis was given as pleomorphic adenoma with extensive squamous metaplasia and focal adipocytic metaplasia. Margins were negative.
Figure 1: (a and b) Computed tomography picture showing a well-defined swelling in the soft palate (c) Grayish white and a well defined solid mass in cut section of the gross specimen (d) Histopathology showing many keratin pearls (hematoxylin and eosin × 40) (e) Histopathology showing many squamous area and keratin (hematoxylin and eosin × 100) (f) Area of adipocytic metaplasia (hematoxylin and eosin × 200) (g) Characteristic area of pleomorphic adenoma showing ductal and myoepithelial proliferation (hematoxylin and eosin × 400) (h) Focal area showing chondromyxoid area (hematoxylin and eosin × 400)

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Currently, the patient is doing well.


  Discussion Top


Pleomorphic adenoma is the most common salivary gland tumor. As such, in minor salivary gland tumors are uncommon and they represent <20% of all salivary neoplasms. The characteristic histopathology of pleomorphic adenoma includes biphasic proliferation of epithelial and myoepithelial cells intermingled with a mesenchymal component.[1],[2],[3]

Pleomorphic adenoma of minor salivary glands has a female predilection. It occurs over a wide age range, and the peak incidence is between the fourth and fifth decades of life. The most common site for minor salivary gland tumors is the palate. Our patient was a 60-year-old female. Clinically, pleomorphic adenoma is a slow-growing, firm, painless mass, which occasionally has an ulcerated surface.[2],[3],[4],[5]

Histopathologically, pleomorphic adenoma exhibits a wide range of morphologic pattern.

Because of the presence of extensive squamous metaplasia and keratin, a variety of differential diagnoses can be considered in the present case. They are conventional SCC, adenoid, or adenosquamous cell carcinoma, mucoepidermoid carcinoma, and even benign condition such as necrotizing sialometaplasia.[4]

Conventional SCC is an important differential diagnosis in cases showing extensive squamous metaplasia like the present case. SCC may invade or entrap normal-appearing salivary glands.[4] The present case was not considered as SCC because of the lack of dysplasia in squamous islands and presence of typical area of pleomorphic adenoma with focal chondromyxoid area.

Adenoid SCC and adenosquamous cell carcinoma were not considered in the present case due to the absence of any true glands/ducts with atypia and absence of intracytoplasmic mucins. There was absence of cellular and nuclear atypia, necrosis, capsular invasion, an aggressive growth pattern, and nerve or surrounding tissue infiltration.[5]

Pleomorphic adenomas, particularly of minor salivary glands of palate, may contain large areas of squamous and mucinous metaplasia, thereby arising the suspicion of mucoepidermoid carcinoma.[3],[4],[5],[6],[7],[8] It is usually distinguished from mucoepidermoid carcinoma by at least focal presence of characteristic ductal and myoepthelial proliferation and myxochondroid stroma. In mucoepidermoid carcinoma, prominent keratinization and keratin pearl formation are rare.[1],[2] In our case, there was extensive squamous metaplasia, but these cells had bland morphology with minimal mitotic activity. In addition, a tiny area of chondromyxoid stroma was identified.

Cribriform structures if present in pleomorphic adenoma may mimic adenoid cystic carcinoma.[3],[5] No such area with atypia was identified in the present case.

Clinically, a diagnosis of necrotizing sialometaplasia or chronic sialadenitis may be considered because of its location in palate. But on histopathological examination, the absence of necrosis and presence of characteristic areas of pleomorphic adenoma showing ductal and myoepithelial proliferation along with chondromyxoid stroma ruled out necrotizing sialometaplasia.[5]

Few cases are reported in English literature with extensive squamous metaplasia.[4],[5],[7],[8] Similar to our case, Brisebois et al. have published one such case with extensive squamous metaplasia and adipocytic metaplasia.[5] They performed immunohistochemistry with markers such as epithelial membrane antigen which was positive in the luminal cells, smooth muscle actin, and s-100 highlighting the myoepithelial cells. In their case, keratin 5/6 and 903 were all positive for the entire specimen.

In an article by Lim et al., the authors have opined that the pattern of cytokeratin expression can be helpful in determining squamous metaplasia. According to them, the cells that express high-molecular-weight cytokeratin (HMW CK) have undergone squamous metaplasia, but those expressing low-molecular-weight cytokeratin (LMW CK) and p63 have not yet undergone squamous metaplasia.[9]

In our case, the gross and microscopic appearance of a well-circumscribed lesion, characteristic area of pleomorphic adenoma, and bland morphology of the squamous islands helped us render a diagnosis of pleomorphic adenoma with extensive squamous metaplasia.

Therefore, it is essential to examine the histopathology carefully so as to arrive at the correct diagnosis and avoid unnecessary extensive surgery.

The treatment of choice is wide local excision.[1],[2] The recurrence rate is around 5%–30% and is associated with incomplete surgical excision. There is also a risk of malignant transformation, usually giving rise to a carcinoma ex pleomorphic adenoma.[5],[6],[7] A close postoperative follow-up is essential.

Our patient had an uneventful postoperative period and is currently under follow-up for 1 year without any evidence of recurrence or malignant transformation.


  Conclusion Top


The awareness of this entity of pleomorphic adenoma with extensive squamous metaplasia is important as it can mimic malignancy.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Friedrich RE, Li L, Knop J, Giese M, Schmelzle R. Pleomorphic adenoma of the salivary glands: Analysis of 94 patients. Anticancer Res 2005;25:1703-5.  Back to cited text no. 1
    
2.
Reddy V, Wadhwan V, Aggarwal P, Sharma P, Reddy M. A benign salivary gland tumor of minor salivary gland mimicking an epithelial malignancy. Contemp Clin Dent 2015;6:247-9.  Back to cited text no. 2
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3.
Lopes MLDS, Barroso KMA, Henriques ÁCG, Dos Santos JN, Martins MD, de Souza LB. Pleomorphic adenomas of the salivary glands: Retrospective multicentric study of 130 cases with emphasis on histopathological features. Eur Arch Otorhinolaryngol 2017;274:543-51. doi: 10.1007/s00405-016-4253-5.  Back to cited text no. 3
    
4.
Sharma S, Mehendiratta M, Chaudhary N, Gupta V, Kohli M, Arora A. Squamous metaplasia in pleomorphic adenoma: A diagnostic and prognostic enigma. J Pathol Transl Med 2018;52:411-5.  Back to cited text no. 4
    
5.
Brisebois S, Chababi Atallah M, Borduas M, Fortier PH. A challenging case of squamous metaplasia in a pleomorphic adenoma: Diagnostic and clinical pitfalls. J Surg Case Rep 2015;2015:pii: rjv113. doi: 10.1093/jscr/rjv113.  Back to cited text no. 5
    
6.
Skálová A, Andrle P, Hostička L, Michal M. Pleomorphic adenoma of salivary glands: Diagnostic pitfalls and mimickers of malignancy. Cesk Patol 2012;48:179-83.  Back to cited text no. 6
    
7.
Goulart MC, Freitas-Faria P, Goulart GR, Oliveira AM, Carlos-Bregni R, Soares CT, et al. Pleomorphic adenoma with extensive squamous metaplasia and keratin cyst formations in minor salivary gland: A case report. J Appl Oral Sci 2011;19:182-8.  Back to cited text no. 7
    
8.
Nasit JG, Dhruva G. Extensive squamous metaplasia with cystic change in pleomorphic adenoma: A potential diagnostic pitfall in fine needle aspiration cytology. Clin Cancer Invest J 2013;2:166-9.  Back to cited text no. 8
    
9.
Lim S, Cho I, Park JH, Lim SC. Pleomorphic adenoma with exuberant squamous metaplasia and keratin cysts mimicking squamous cell carcinoma in minor salivary gland. Open J Pathol 2013;3:113-6.  Back to cited text no. 9
    


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