|Year : 2014 | Volume
| Issue : 2 | Page : 179-181
Warthin tumor with extensive squamous and mucinous metaplasia: Pathologist's dilemma
JB Leena, Reshma G Kini, Sumanth Devaraju, Subhan R Ali
Department of Pathology, Father Muller Medical College, Mangalore, Karnataka, India
|Date of Web Publication||1-Jul-2014|
J B Leena
Department of Pathology, Father Muller Medical College, Kankanady, Mangalore - 575 002, Karnataka
Source of Support: None, Conflict of Interest: None
Secondary changes in Warthin tumor (WT) are not uncommon. Diagnostic error in Fine Needle Aspiration (FNA) is caused by a lack of typical features and the presence of individual atypical squamous cells in a necrotic background, mimicking carcinoma. Mucoepidermoid carcinoma, squamous cell carcinoma, and oncocytoma are the commonest tumors diagnosed in place of WT, the source of error being the presence of squamous metaplasia in the former two and the absence of the lymphoid cells in the latter. We report a case of WT with extensive squamous and mucinous metaplasia with desmoplasia and a certain degree of atypia which was diagnosed on FNA as Low Grade Mucoepidermoid Carcinoma (LGMEC). Prior FNA of the lesion may be the reason for the extensive metaplasia, desmoplasia, as well as atypia in our case. An extensive histopathological examination of the superficial parotidectomy specimen helped us arrive at the correct diagnosis.
Keywords: Mucinous metaplasia, squamous metaplasia, Warthin
|How to cite this article:|
Leena J B, Kini RG, Devaraju S, Ali SR. Warthin tumor with extensive squamous and mucinous metaplasia: Pathologist's dilemma. Muller J Med Sci Res 2014;5:179-81
|How to cite this URL:|
Leena J B, Kini RG, Devaraju S, Ali SR. Warthin tumor with extensive squamous and mucinous metaplasia: Pathologist's dilemma. Muller J Med Sci Res [serial online] 2014 [cited 2021 Sep 28];5:179-81. Available from: https://www.mjmsr.net/text.asp?2014/5/2/179/135768
| Introduction|| |
Warthin tumor (WT) is a benign tumor, seen most commonly in middle age. The risk in smokers is eight times that of nonsmokers.  Some tumors, variously termed, infarcted, infected, or metaplastic, account for 6% to 7% of Warthin tumors. 
Fine Needle Aspiration (FNA) of salivary glands is a good diagnostic test with reasonable sensitivity and specificity. False-negative results in a malignancy are either due to hypocellular aspirate in a cystic lesion or due to errors of underdiagnosing low-grade tumors which have bland cytologic features. False-positive diagnosis emanate from overcalls of reactive changes that occur in the setting of associated inflammatory reactions.  Awareness of such changes could enhance the accuracy of cytopathology reports and make FNA a reliable mode of preoperative diagnosis. 
| Case Report|| |
A 36-year-old man presented with a slowly growing painless mass in the right parotid region for 2 years with recent onset of mild facial nerve weakness. The mass was firm, mobile, and measured around 4 × 3 cms. Prior FNA study elsewhere had been reported as suggestive of malignant salivary gland neoplasm.
FNA of the mass was cellular and showed sheets of squamous cells with mildly pleomorphic vesicular nuclei in a background of mucin and scattered lymphocytes. Some of these cells also showed vacuolated cytoplasm [Figure 1]a and b. Based on these findings, a possibility of mucoepidermoid carcinoma was considered.
|Figure 1: (a) May-Grünwald-Giemsa stain, (MGG) stained FNA smear showing mucoid background, (b) Papanicolaou stain (PAP) stained FNA smears show mildly atypical squamous cells MGG = May-Grünwald-Giemsa stain, FNA = Fine Needle Aspiration, PAP = Papanicolaou stain|
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Superficial parotidectomy specimen showed a grey white well-encapsulated solid lesion measuring 3 × 3 cms with cystic spaces [Figure 2].
Microscopy revealed a well-circumscribed tumor with multiple cystic spaces lined predominantly by metaplastic squamous and mucinous cells arising from oncocytic epithelium. The fact that they were metaplastic was evident from areas, which showed fusion of squamous cells with the oncocytes. Islands of these cells were seen extending into the subepithelium. Subepithelium showed lymphoid follicles and large areas of fibrosis adjacent to the cysts as well as the islands which imparted pseudoinfiltrative appearance. The oncocytic epithelium constituted only a small percentage of the epithelial component [Figure 3]. Cholesterol clefts were also seen. A diagnosis of WT with extensive mucinous and squamous metaplasia was made.
|Figure 2: Gross: Superficial parotidectomy specimen showing a grey white encapsulated tumor with focal hemorrhages|
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|Figure 3: Microscopy showing cystic spaces lined by oncocytic epithelium and merging of squamous islands with the oncocytic epithelium|
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| Discussion|| |
WT is a benign tumor commonly encountered in salivary gland specimens. WT occur almost exclusively in the parotid, is slightly more common in females, shows an association with cigarette smoking and may be bilateral in about 10% of the cases. Studies demonstrate that this tumor is associated with cigarette smoking, which may be due to irritation of the ductal epithelium by tobacco smoke that initiate tumorogenesis. The most accepted hypothesis about the origin of WT is that it develops from salivary duct inclusions in the lymph nodes. 
On palpation, most WT feel soft or boggy but in situations of increased fluid accumulation they may feel quite tense and firm. The patients can be otherwise asymptomatic or can have facial pain. Facial nerve palsy may be seen in tumors associated with inflammation and fibrosis, which can be mistaken for malignant tumor. ,
Warthin tumors have a characteristic cytomorphologic appearance represented by three main components -
oncocytes, lymphocytes, and the fluid background. Cytological difficulties can be divided into three areas:
- Absence of one or more diagnostic components;
- Squamoid pattern; and
- Mucinous metaplasia. The fluid of WT often imparts a dirty background appearance that may be confused with tumor necrosis. 
Mucoepidermoid carcinoma, squamous cell carcinoma, and oncocytoma are the commonest tumors diagnosed in place of WT. Our case showed extensive areas of mucinous and squamous metaplasia diagnosed as Low Grade Mucoepidermoid Carcinoma (LGMEC) on FNA.
To add to these challenges, it has been shown that metaplastic/reparative changes can occur in benign salivary gland neoplasms due to physical trauma induced by FNA. These changes include squamous metaplasia, infarction, necrosis, subepithelial stromal hyalinization, acute/chronic hemorrhage, inflammation with multinucleated giant cells, granulation tissue with subsequent fibrosis, cholesterol cleft formation, pseudoxanthomatous, reaction and microcystic degeneration. 
In the present case, FNA showed mucoid dirty background and squamous epithelial cell clusters. However, oncocytes were not visualized in the smears and there were few lymphocytes which was misleading and lead to the diagnosis of LGMEC. Subsequent histopathology showed widespread squamous and mucinous cell clusters with fibrosis and pseudoinfiltrative appearance leading to a diagnostic dilemma. Patient had mild facial nerve palsy and history of previous FNA, the possibility of LGMEC had to be ruled out.
The key to the diagnosis of Warthin was lack of tumor infiltration into the surrounding normal parenchyma. Another important differentiating feature is the evidence that the metaplastic squamous cells merged with the oncocytes which is not seen in mucoepidermoid carcinoma. Squamous metaplasia of WT usually lacks keratinization, which is seen in most squamous cell carcinoma. 
Extensive areas of mucinous and squamous metaplasia, pseudoinfiltrative appearance of the metaplastic squamous epithelium in the residual tumor often invite an erroneous diagnosis of squamous cell or mucoepidermoid carcinoma. But lack of true infiltrative growth into the surrounding parenchyma and merging of the squamous islands with oncocytic epithelium should point to the correct diagnosis. Though literature gives evidence of squamous and mucinous metaplasia, this case showed extensive areas of mucinous and squamous metaplasia. This could possibly be due to the metaplastic and reparative changes that happened subsequent to the previous FNA. , Our case did present with mild facial nerve palsy which is explained by the extent of fibrosis. 
We would like to highlight post FNA tissue changes in this case as we need to be aware of such changes to avoid potential diagnostic errors in the interpretation of specimens. To date, surgical excision is considered the treatment of choice in the management of Warthin tumors. Awareness of potential diagnostic difficulties in some cases invites surgery over conservative management. 
| Conclusion|| |
Extensive squamous and mucinous metaplasia occuring in WT can mimic low-grade tumors such as mucoepidermoid carcinoma on FNA. Furthermore, the secondary changes observed in this case are probably due to the previous FNA. Awareness of the various secondary changes that can occur following FNA will help prevent an erroneous interpretation in FNA setting and direct correct management.
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[Figure 1], [Figure 2], [Figure 3]