Epithelial-Myoepithelial Carcinoma of Parotid Gland—A Surprising Clinical Entity-医学工程与组织工程研究-医学新闻-世界最新医学信息文摘

Epithelial-Myoepithelial Carcinoma of Parotid Gland—A Surprising Clinical Entity

Jaimanti Bakshi, Grace Budhiraja, Karan Gupta, Sourabha K Patro, Nalini Gupta

Department of Otolaryngology & Head-Neck Surgery & Department of Cytopathology, PGIMER, Chandigarh, India

ABSTRACT

Objective: Objective of this study is to highlight the importance of considering clinical and radiological findings in pa-rotid tumors before operating tumors with high suspicion of malignancy though reported as benign on histopathology. Material and Methods: 20 years old female patient underwent radical parotidectomy for epithelial-myoepithelial carci- noma of the left parotid gland which was diagnosed on FNAC. Contrast CT and contrast MRI also showed a tumor in- volving left parotid gland with destruction of ramus of mandible and loss of tissue planes medially & laterally. Facial nerve was infiltrated by tumor, thus sacrificed. Post operatively, patient had left facial palsy and was discharged after 7 days without any other sequelae. Postoperative histopathology showed pleomorphic adenoma with positive resection margins medially, superiorly & posteriorly. No further treatment was given in view of the benign nature of the tumor. Results: Patient was kept on monthly follow up and was disease free at one year follow up. Conclusion: Aggressive surgical treatment should be planned for malignant parotid tumors to give a better tumor free survival. Misdiagnosis can occur on FNAC as it can hit only one part of the tumor thus missing a malignant tumor or can interpret pleomorphic adenoma as epithelial-myoepithelial carcinoma.

Keywords: Myoepithelial; Parotid; Carcinoma; Pleomorphic Adenoma

1. Introduction

Pleomorphic adenoma is the most common neoplasm of both the major and minor salivary glands. It is composed of an array of tissue types, of both epithelial and mesen- chymal origins, and is regarded as benign in clinical be- havior, but has the potential to undergo malignant trans- formation. Epithelial-myoepithelial carcinoma (EMC) is a rare biphasic tumor of the salivary glands typically arising in the parotid. Fine needle aspiration cytology is widely used in the initial investigation of salivary gland swellings and whilst the cytological features of this tu-mour have been described they are not well recognized. Epithelial-myoepithelial carcinoma (EMC) is a rare type of malignant tumor, accounting for about 1% of all sali-vary gland tumors [1,2] and recognizes a typical biphasic pattern: a central ductular structure, often containing eosinophilic material surrounded by clear cells of myoe- pithelial origin. It was firstly described as a glycogen- rich or clear cell adenoma because of the clear cell com- ponent. Donath et al. [3] noted that the myoepithelial component was an integral part of the tumor and in 1972 he introduced the term epithelial-myoepithelial carcinoma while describing this entity where he described the clini- copathological features of a case of epithelial-myoe-pithelial carcinoma of the parotid gland and highlighted the importance of awareness of this tumor in the differ- ential diagnosis of biphasic tumors on Fine needle aspi-ration cytology. In 1991, the WHO recognized EMC as a distinct entity and subtype of salivary gland adenocar- cinoma, and it became part of the new classification system [4]. It is currently felt that most malignant sali-vary gland tumors arise from either the excretory duct or the intercalated duct reserve cell. Either of these two cells have the potential for differentiation into a variety of epithelial tumor. EMEC arises most commonly in the parotid gland but has also been described in the sub-mandibular gland, in the minor salivary glands and pal-ate [4,5]. There is a female predominance, with a peak occurrence in the seventh decade [4]. EMEC is a low- grade malignant tumor that may commonly recur locally after resection. Distant metastasis rarely occurs [3-5]. The lesion may be encapsulated, but the capsule may be incomplete and tumor nodules extend through it. Nu-clear pleomorphism and metastasis are rare, although perineural and vascular invasion may occur. Because of cytological bland appearance; this tumor has been de-scribed as a type of adenoma. Prognosis is usually fa-vorable.

2. Case Report

2.1. History

A 22 years old woman presented to our institution with a 6 months history of a painless swelling in the region of the left parotid gland. On examination, a 7 cm diameter, firm tumor mass was palpable in the gland. The growth was well demarcated, extending from zygomatic arch to angle of mandible with a smooth external appearance. It had a moderately firm consistency with fixity to neigh- boring tissues. It was non-tender with no associated facial weakness or cervical lymphadenopathy. The oral cavity was normal on inspection.

Ultrasonography done at another center revealed nor- mal parotid glands with hypoechoic thickening with amorphous calcification seen deep to the gland. Fine needle aspiration done in private hospital showed the presence of round cells with moderate to abundant cyto- plasm, which was vacuolated in few cells. Nuclei were round to oval with finely stippled cytoplasm. Some of the cells were binucleate. The cytological interpretation was not specific. Possibility of osteogenic, chondrogenic or reticuloendothelial cell origin was suggested.

Fine needle aspiration cytology done at our institute showed predominant scattered and occasional clusters of malignant cells, the tumor cells were round to oval with eccentrically placed nuclei, prominent nucleoli and mod-erate to abundant amount of basophilic cytoplasm. Many multinucleated giant cells, atypical mitotic figures were also noticed. Overall features were suggestive of myoe- pithelial, epithelial carcinoma (Figure 1).

MRI done at our institute-revealed a7 × 5 × 5 cm lobulated soft tissue mass extending on both sides of leftmandible, heterogeneously hyper-intense on T2 (Figure 2), iso-intense on T1 (Figure 3) showing sunray type of pattern with few hypointense areas suggestive of necrosis. Laterally the mass was displacing and compressing the parotid gland posterolaterally with maintained fat planes and masseter muscle anterolaterally, superiorly mass was involving both coronoid and condylar processes of man-dible. Medially it was indenting the lateral wall of left parapharyngeal space with normal nasopharynx. No sig-nificant lymphadenopathy was seen.

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