Introduction

Salivary gland tumors most commonly involve the parotid gland. Among all the salivary gland tumors, 80% are benign and of all the benign tumors 80% originate from the parotid gland [1, 2]. The pleomorphic adenoma is the most common benign tumor whereas mucoepidermoid carcinoma is the most prevalent malignant tumor [2, 3]. Mucoepidermoid carcinoma is comprised of different proportions of epidermoid, mucous, and intermediate cells which further divides it into low-grade and high-grade mucoepidermoid carcinoma [4].

To diagnose the parotid mass fine needle aspiration cytology (FNAC) is a common investigation to proceed with and decisions can be taken for the surgical management and extent of the surgery. Here we present a case of Mucoepidermoid carcinoma of the parotid gland mimicking pleomorphic adenoma on cytology.

Case Report

A 17-year-old female presented with slow-growing painless swelling below the right ear for two years. The patient sought medical treatment locally and had a history of incision and drainage of pus 3 weeks back. Following the drainage, incision site healing occurred in the upper part, but the patient developed ulceration over the lower aspect of the incision site. Her medical history was unremarkable. On clinical examination, a single firm swelling of 3 × 2 cm with central ulceration and erythematous overlying skin just below the right ear lobule was present. The healed scar of the previous incision showed fixity to the skin in its upper aspect; the rest of the overlying skin mobility appeared normal and a healing ulcer was present in the lower aspect of the previous incision. On palpation, there was no other neck swelling, and no cervical lymph node enlargement was seen. Clinical examination appeared to be a benign parotid swelling on the basis of the long duration of progression, no associated pain, and no sudden increase in swelling [Fig. 1]. Further investigation proceeded and fine needle aspiration cytology was performed.

Fig. 1
figure 1

Pre-operative clinical presentation

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FNAC smears showed features suggestive of Pleomorphic Adenoma. [Fig. 2] On basis of the cytology report, superficial parotidectomy was done under general anesthesia and the specimen was sent for histopathological evaluation. Grossly the tumor was soft to firm measuring 2.5 × 2 × 1 cm. Formalin-fixed, paraffin-embedded tissue sections were stained with hematoxylin and eosin (H&E), and periodic acid Schiff (PAS) for routine histologic review. On histopathology diagnosis of Low-grade Mucoepidermoid carcinoma was given. [Fig. 3] The patient was followed and there was no evidence of recurrence [Fig. 4].

Fig. 2
figure 2

Shows sheets of the mononuclear benign-looking pump to spindle cells in a myxoid background on cytological examination

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Fig. 3
figure 3

Shows histopathological features of low-grade mucoepidermoid carcinoma of the parotid gland

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Fig. 4
figure 4

Post-operative follow-up presentation

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Results

Histopathology revealed periodic acid Schiff (PAS) positive low-grade mucoepidermoid carcinoma in the parotid gland [Fig. 3] showing small nests, cords, and cystic spaces of epidermoid cells along with intermediate cells and clusters of monocytes with clear cell change with focal changes of extracellular mucin and intracellular keratinization. All the margins of the tumor except the tail were uninvolved and adequate margin was excised.

Whereas preoperatively the cytological examination [Fig. 2] revealed sheets of mononuclear ductal cells with plump to oval myoepithelial cells in the myxoid degeneration background suggesting pleomorphic adenoma.

Discussion

Fine needle aspiration cytology is a minimally invasive procedure with good accuracy commonly performed preoperatively in parotid swelling to make a diagnosis. Mucoepidermoid carcinoma is the most common malignant neoplasm of the salivary gland and the parotid gland is most commonly involved [5]. High-grade tumors are easily diagnosed when compared to low-grade tumors due to the presence of epidermoid cells, intermediate cells, and mucous cells simultaneously in the mucinous background [6]. Low-grade Mucoepidermoid carcinoma is a diagnostic challenge in cytology, it can be misdiagnosed as a benign lesion like a pleomorphic adenoma or cyst [7, 8].

In our case, due to low cellularity and relatively benign-looking cytological feature with the myxoid background, it was misdiagnosed as a pleomorphic adenoma of the parotid gland which is the most common benign neoplasm.

Conclusion

Fine needle aspiration cytology alone is not completely reliable to diagnose mucoepidermoid carcinoma of the parotid gland especially low-grade variants as there is the simultaneous presence of epidermoid or squamoid cells, intermediate cells, and mucous cells in the mucinous background and constitutes a definitive diagnosis. It can be missed and difficult to obtain in the cytology samples. High clinical suspicion should always lead to the diagnosis and further evaluation for the complete removal of the tumor [9].