Pleomorphic adenoma is a benign, slow-growing neoplasm that most commonly affects the parotid gland. It has epithelial, myoepithelial, and stromal components. The prognosis is generally good after the surgical removal, however, there is an increased incidence of recurrence particularly if the parotid gland is affected.
Pleomorphic adenoma or benign mixed tumor, occur most frequently (85%) in the parotid glands , followed by the minor salivary glands in 10% of the cases, and then by the submandibular glands at 5% . The adenoma presents as a small, mobile, slowly growing, painless mass of 2-6 cm; however, occasionally much larger tumors have been encountered . Patients have varying symptoms, which may depend on the location of the tumor, and may include hoarseness of voice, dyspnea, and difficulty in chewing and eating.
The tumors occur most frequently in middle-aged women. They originate in most cases from the superficial lobe of the parotid gland and present as a swelling of the gland below the ear; however, they can develop in the deep lobe of the parotid gland, where they will not be easily noticed in early stages . Tumors of the deep lobe of the parotid gland, and of the minor salivary glands sometimes appear in the parapharyngeal space . More common locations for adenomas of the minor salivary glands are the hard and soft palate, and the mucosa of the lip . Most tumors are solitary, but bilateral tumors have also been found . The facial nerve is rarely involved.
The adenomas are often encapsulated. The histological pattern varies case by case [3[. All tumors are mixtures of epithelial cells, myoepithelial and basal cells, with varying contributions from stroma; using the relative amounts of different cell types and stroma for predicting future outcomes has not yet met with success .
Although PA is a benign tumor, it can become malignant. Surgical removal of the tumor by enucleation –or preferably by parotidectomy at the first incidence - is the cornerstone of treatment. Surgery has to be done carefully to preserve the facial nerve and to avoid rupture, which could lead to recurrence of the tumor.
Pleomorphic adenomas of the lacrimal glands (PALG) constitute about a tenth of the lacrimal gland tumors. Patients with PALG present with slowly progressing proptosis. The treatment for PALG is total removal of the tumor .
The radiological tools for the diagnosis and differentiation of salivary gland disease are computerized tomography (CT) scans, magnetic resonance imaging (MRI), and ultrasonography  . MRI may be the instrument of choice over CT scan, because of its superior definition of soft tissue and tumor margins . Ultrasound may also be used to serve as the first diagnostic tool; it can differentiate malignant lesions from benign ones with very high accuracy (96%), and can successfully predict PA cases . Apart from location, shape, dimensions and margin , ultrasound can distinguish between cystic and solid masses, and between intra- and extracapsular tumors . It can also be used for guiding fine needle biopsy .
Fine needle aspiration biopsy is also an important tool for preoperative diagnosis; it is safe and reliable but its sensitivity is variable and is more accurate for the diagnosis of benign lesions than for malignant ones   .
Because of the diverse histological appearance of PAs, it may not be easy to differentiate them histologically from other neoplasms, such as myoepithelioma or some carcinomas .