**4. Overview**

In this chapter, the intraoral SG tumours and tumour-like lesions are being discussed under following six headings for better understanding of these tumours and related diagnostic challenges and pitfalls.

### **4.1 Matrix-containing tumours**

The matrix producing tumours of intraoral SGs are pleomorphic adenoma (PA), adenoid cystic carcinoma (ADCC), polymorphous adenocarcinoma (POA). Carcinoma ex pleomorphic adenoma (CEPA), epithelial-myoepithelial carcinoma (EMC) are other matrix producing tumours that can also occur in intraoral SGs.

#### *4.1.1 Pleomorphic adenoma (PA)*

Pleomorphic adenoma is the most common benign tumour of SGs. Although, majority of PA occur in parotid gland**,** some studies documents PA as most common neoplasm in intraoral minor SGs [2, 4]. In the oral cavity, it usually presents as a solitary nodule or mass in the palate, sometimes with obstructive clinical symptoms.

**Key cytological features –** Smears show variable cellularity with cells arranged in clusters and sheets, embedded in a fibrillary chondromyxoid ground substance or matrix (**Figure 1**). The majority of cells are myoepithelial which may be ovoid, spindle, plasmacytoid, epithelioid, clear or stellate shaped. The nuclei of cells are round to oval, often with eccentric nucleus with bland finely granular chromatin and inconspicuous nucleoli. The cytoplasm is pale with well-defined cell borders. Stripped naked nuclei are not seen. PA may show diverse metaplastic changes including squamous metaplasia with or without keratinisation, oncocytic, clear cell, sebaceous, lipomatous and cartilaginous metaplasia. Hyaline globules can be seen. The prototypical PA is placed in benign category (IVA) of the Milan system.

#### **Diagnostic challenges and pitfalls – Pleomorphic Adenoma (PA)**

a.Sometimes, aspirate from PA may consist of only chondromyxoid substance without presence of epithelial and myoepithelial cells. The diagnosis of a neoplasm can be suspected but reaspiration is needed to rule out the possibility of other matrix producing tumours such as adenoid cystic carcinoma (ADCC) which can also occur at various intraoral locations. Both of these tumours have fibrillar metachromatic matrix and may show formation of hyaline globules. However, the matrix in PA is fibrillar with frayed edges (**Figure 2a**) while in ADCC the matrix is in form of beaded finger-like fragments, acellular spheres and tubules with sharply defined edges (**Figure 2b**) [15, 16]. Cellular PA with scant matrix particularly may resemble solid variant of ADCC. The cells of ADCC are basaloid and careful examination of nuclear chromatin of cells reveals distinguishing features. The cells in PA have bland finely granular chromatin while the cells of ADCC have coarse nuclear chromatin, high nuclear-cytoplasmic (N:C) ratio, scant cytoplasm and nucleoli [15]. The cells of ADCC may show focal nuclear moulding. Stripped naked nuclei can be seen in ADCC but not in PA. However, in challenging cases, it is not always possible to distinguish between the two entities. Such cases may be placed in SUMP category (IVB) of the Milan system. Follow-up and excision may be advised keeping clinical context in mind.

#### **Figure 1.**

*1a: FNAC smear showing abundant chondromyxoid matrix with embedded cells in a case of pleomorphic adenoma (May-Grunwald Giemsa stain x 40), 1b: Corresponding histopathology showing nests, interlacing cords and strands of epithelial and myoepithelial cells in a myxoid stroma (Haematoxylin & Eosin x 40).*

*Cytopathology of Intraoral Salivary Gland Tumours and Tumour-Like Lesions… DOI: http://dx.doi.org/10.5772/intechopen.98872*

#### **Figure 2.**

*2a: Smear showing abundant fibrillar metachromatic matrix with frayed edges in pleomorphic adenoma (May-Grunwald Giemsa stain x 40), 2b: Showing metachromatic matrix in form of acellular beaded, fingerlike fragments and hyaline spherical globules with well-defined borders in a case of adenoid cystic carcinoma (May-Grunwald Giemsa stain x 40).*


#### **Figure 3.**

*3a: FNAC smear showing pleomorphic adenoma with squamous metaplasia (arrows) (May-Grunwald Giemsa stain x 4), 3b: Corresponding histology showing squamous metaplasia with evidence of keratinisation (arrow) surrounded by myxoid stroma (Haematoxylin & Eosin x 40).*

of high grade atypical features in cells (**Figure 4**) and even a focal presence of areas depicting conventional PA consisting of benign cell clusters and chondromyxoid matrix (**Figure 4**), should lead to the diagnosis of CEPA [18, 19].


#### **Figure 4.**

*4a: Showing malignant cells with high N:C ratio and hyperchromatic nuclei (black arrows) in a case of carcinoma ex-pleomorphic adenoma with evidence of metachromatic matrix of pre-existing pleomorphic adenoma (white arrow) (May-Grunwald Giemsa stain x 40), 4b: Corresponding histology showing sheet of malignant cells (white arrow) arising in background of myxoid stroma (black arrow) of pleomorphic adenoma (Haematoxylin & Eosin x 10).*

#### **Figure 5.**

*5a: FNAC smear showing population of myoepithelial cells (black arrow) with metachromatic matrix (white arrow) in a case of myoepithelial predominant pleomorphic adenoma (May-Grunwald Giemsa stain x 40). 5b: Smear showing myoepithelial cells with pale to clear cytoplasm (arrow) in a case of a myoepithelioma (May-Grunwald Giemsa stain x 40).*

and is not of much significance as both entities are benign (Milan system category IVA) and management is almost similar.
