The value of fine needle aspiration cytology in the clinical management of rare salivary gland tumors

Abstract Salivary gland tumors are relatively rare neoplasms, mostly located in the parotid gland, and few are malignant. Preoperative evaluation of salivary gland tumors includes fine needle aspiration cytology (FNAC). Objective The purpose of this study was to determine the importance of FNAC in the evaluation of rare salivary gland neoplasms. Material and Methods Four cases of rare salivary gland tumors were included, which were preoperatively assessed by clinical investigation, computed tomography, and FNAC. Results The presented cases include myoepithelial carcinoma, oncocytic carcinoma, undifferentiated lymphoepithelial carcinoma, and marginal zone lymphoma. Conclusion FNAC is a reliable diagnostic tool for common salivary gland neoplasms; however, rare tumors often represent diagnostic challenges. Clinical relevance In such rare tumors, the role of aspiration cytology may be limited to establishing the dignity of the lesion (benign/malignant). This knowledge enables the surgeon to choose the most appropriate therapeutic procedure. A definitive diagnosis of rare tumors (either epithelial or nonepithelial) is obtained by histological examination; cytology is limited in this regard due to overlapping features.


Introduction
Salivary gland tumors are relatively rare neoplasms, with an incidence of about 2.5-3 cases per 100,000, and represent about 3% of all head and neck tumors.
Etiology of salivary gland tumors is still under debate; it is presumed that smoking, viral infections, and genetic predisposition may all play a significant role in their pathogenesis. Ionizing radiation is probably the only well-established risk factor with documented role in the etiology of these tumors 15,32 .
The initial preoperative evaluation of salivary gland tumors includes patient history, followed by thorough clinical examination of the face and neck, imaging tests (especially ultrasonography and computed tomography), and fine-needle aspiration cytology (FNAC). FNAC is a preferred method for obtaining morphological diagnosis prior to surgery. It is relatively low cost, less invasive, and has the ability to offer preoperative diagnosis, which makes it a preferred method of diagnosis. FNAC is effective in providing rapid morphological assessment of lesions, offering valuable information about the origin (salivary or nonsalivary), nature (benign or malignant) and/or grade (low or high grade) of the tumors. Information thus obtained is an invaluable aid in proper clinical and surgical management 4,6 .
Although this is valid for most cases, cytology alone, however, cannot provide a definitive diagnosis in some cases where histological diagnosis is the gold standard. FNAC has limitations, especially in identifying rare entities and distinguishing lesions that have overlapping cytological features, which is often the case in salivary gland tumors 3  This complex classification is based on histological features and has the advantage of estimating the prognostic and therapeutic outcomes based on the different behavior of each tumor type. The great diversity of these tumors is related to various cell types found in salivary glands (ductal, acinar, myoepithelial, and basal cell types) 5 . This plethora of diverse types, however, also turns FNAC diagnosis into a challenging task.    follow-up, one month after radiotherapy. Her general condition had improved slightly.

Case 3
A 66-year-old male patient presented with facial asymmetry caused by a painless mass on the right parotid area, discovered a year ago, that showed accelerated growth in the past four months. Clinical examination revealed a firm, irregular, 5 cm diameter mass arising in the right pre-auricular region, fixed to deeper tissues and overlying skin, without clinical evidence of facial nerve involvement. Ultrasonography showed a hypoechogenic mass of 40×33 mm with irregular contour, heterogeneous structure, and rich vascular image, confirmed by computed tomography as well, without lymph node involvement.  During these visits, his general condition seemed to  Lymphoepithelial carcinoma has a strong tendency to metastasize, first to the parotid nodes, followed by the upper cervical and retro-auricular lymph nodes, later to the supraclavicular and paratracheal nodes.
Distant metastases usually involve the lungs, liver, bones, and brain. It has a better prognosis than other undifferentiated carcinomas of the salivary glands, perhaps because of the lymphoid stroma, which has a role in limiting the tumor's aggressiveness 28 .
Marginal zone lymphoma is an extra nodal low grade B-cell non-Hodgkin lymphoma that may affect the parotid gland. Other than the stomach, the salivary gland is one of the most common sites involved by extra nodal marginal zone lymphomas of mucosaassociated lymphoid tissue (MALT) 16 . Characteristically, it presents as a painless, progressively growing mass 13  Some studies found that prognosis is better in cases that arise in the background of Sjögren's syndrome 17 .
FNAC is a valuable diagnostic tool that offers J Appl Oral Sci. 2018;26:e20170267 10/11 the surgeon the ability to risk-stratify patients, to counsel them appropriately, and to avoid surgery in selected cases. Moreover, should FNAC confidently prove the existence of a benign process, facial nerve preservation must be attempted 20 . It is important to mention that, to maintain its high diagnostic accuracy as emphasized by Díaz, et al. 12 (2014), all personnel involved in the process of salivary gland FNAC need to be continuously trained in this rather challenging area of diagnostic cytology 30,33 . Salivary gland cytology is an exciting branch of cytology that over the years has matured for the development of its own unified system for reporting, the Milan classification 25 .

Conclusion
The primary role of FNAC in salivary gland tumors is to offer a morphological diagnosis whenever that is possible. This is possible in most cases; however, in rare neoplasms the cytological diagnosis is difficult, often being only indicative of the nature of the lesion rather than offering specific diagnosis. For cases with discrepancy between cytological and clinical impressions (especially in cases of rare malignant tumors, such as those presented herein), histological examination remains the gold standard.
Due to frequently overlapping histological features of various salivary gland neoplasms, the definitive diagnosis of rare salivary gland tumors (epithelial or non-epithelial) should always be made by histolopathology. Preoperative cytology is useful for the diagnostic triage of salivary masses but the precise diagnosis may sometimes be difficult to interpret by cytology alone.