Diagnostic utility of FNAC in salivary gland tumors

Salivary gland neoplasms make up 6% of all head and neck tumors. An estimated 700 deaths (0.4 per 100,000 for males and 0.2 per 100,000 for females) related to salivary gland tumors occur annually. Patients with malignant lesions typically present after age 60 years, whereas those with benign lesions usually present before 50 years.
 

There are five broad categories of salivary gland neoplasms:

• Malignant epithelial tumors (Acinic cell carcinoma ,Mucoepidermoid carcinoma, Adenoid cystic carcinoma ,Polymorphous low-grade adenocarcinoma)
• Benign epithelial tumors (Pleomorphic adenoma, Myoepithelioma',Warthins tumor, Oncocytoma)
• Soft tissue tumors (haemangiomas,Lymphangiomas)
• Hematolymphoid tumors ( Hodgkins lymphoma)
• Secondary tumors.

Clinical features
Slowly increasing painless swelling in oral and perioral regions of the mouth are seen, in case of benign lesions. Malignant tumors can cause facial paralysis, numbness of face, difficulty in mastication and swallowing. Submandibular neoplasms often appear with diffuse enlargement of the gland, whereas sublingual tumors produce a palpable fullness in the floor of the mouth. Painless masses on the palate or floor of mouth are the most common presentation of minor salivary neoplasm. Laryngeal salivary gland neoplasms may produce airway obstruction, dysphagia, or hoarseness. Minor salivary tumors of the nasal cavity or paranasal sinus can manifest with nasal obstruction or sinusitis.

Fine needle aspiration cytology as diagnostic tool:
FNAC provides useful preoperative information about a mass lesion arising in the salivary gland. The sensitivity and specificity ranges from 60% to 100% and 90% to 100%, respectively. False-negative and false-positive results occur in salivary gland FNACs. False-negative results are due to bland cytologic features and the difficult evaluation of hypocellular cystic lesions, while false-positive cases are mainly due to associated inflammatory reactions.

FNAC of normal salivary gland: The acinar cells are arranged as grape-like clusters, composed of round or pyramidal cells, usually with uniform eccentric nuclei and abundant granular or vacuolated cytoplasm. Duct cells often form small groups or linear arrangements and appear crowded compared with acinar cells because of the lesser amount of cytoplasm that they possess. Duct cells are smaller than acinar cells, and if they lose their cytoplasm, they can easily be confused with lymphocytes. Sometimes, adipocytes and constituents of salivary gland tissue are seen.
FNAC of common salivary gland tumors:

Pleomorphic adenoma: Myoepithelial and ductal cells present in various proportions are seen. In many cases, myoepithelial cells dominate the smear, forming irregular tissue fragments and scattered background single cells. The myoepithelial cells are in form of plasmacytoid, spindle or stellate shaped with occasional, clear cell changes. Ductal cells are in form of flat sheets composed of small cuboidal cells with round nuclei. Stroma, is seen often as the metachromatic, magenta chondromyxoid matrix. There is overall fibrillary appearance of the matrix.

Warthin tumor: Small flat sheets of oncocytes & scattered lymphocytes are seen in granular "cystic" background. The oncocytes display abundant granular cytoplasm with sharp cytoplasmic borders and bland nuclear features. Lymphoid component shows small, mature background lymphocytes. Rarely, metaplastic squamous and sebaceous gland cells are seen.

Oncocytoma: Oncocytes are present as cohesive 3-dimensional clusters and are usually 3 or more cells thick. The nuclei often exhibit mild atypia and prominent nucleoli. However, occasionally significant nuclear pleomorphism may be seen, but mitotic figures are uncommon. The cytoplasm may appear dense bluish gray, and the cytoplasmic granules, representing numerous mitochondria, may be difficult to detect. Lymphocytes or other cell types are absent or very rare.

Low-grade mucoepidermoid carcinoma: The cellular component of MEC shows a mixture of mucus-secreting cells and goblet cells. Mucus-secreting cells exhibit abundant foamy or vacuolated cytoplasm, low N/C ratios, and loose cellular groups. Small uniform cells with scant cytoplasm are present as tight cohesive clusters.

Acinic cell carcinoma: Smears are quite cellular, showing both single cells and large irregular clusters. The peripheral borders of the cluster demonstrate frayed borders, whereas central part of the cluster often show vessel like structures. Well-differentiated acinic cell carcinoma closely resemble normal acinar cells, are large and polyhedral with abundant bluish gray vacuolated and granular cytoplasm and eccentric nuclei. The cytoplasmic granules are much larger than the granules of oncocytic cells.

Adenoid cystic carcinoma: The cytologic architecture frequently mimics the histologic patterns showing cribriform or tubular structures. The chromatin appears coarse but uniform without identifiable nucleoli, and nuclear pleomorphism is minimal. The background of adenoid cystic carcinoma usually is populated by scattered naked nuclei of tumor cells. The stroma in classic cribriform or tubular adenoid cystic carcinoma shows balls or spheres and cylinders of various sizes. The interface between tumor cells and stroma often is sharply demarcated.

Salivary duct carcinoma: Cellular smears are seen with tumor cells showing cribriform or pseudopapillary formations often associated with necrosis Nuclei are large and irregular with thickened membranes and prominent nucleoli. The cytoplasm is generally moderate to abundant and appears eosinophilic. Bands of hyalinized collagen are seen,which are considered to be stromal response to tumor infiltration.

Conclusion: FNAC is a minimally invasive technique that is known to play an important role in the diagnosis and management of patients with salivary gland tumors. The heterogeneity of benign and malignant tumors with similar cytologic features accounts for indeterminate diagnosis. In such situations, biopsy along with histo-chemical evaluation is indicated to arrive at definitive diagnosis.

Posted in: Medicine