Pleomorphic Adenoma. The impersonator- a case report and review.

The curious case-

A 35-year-old female patient reported to the outpatient department of Fatima Hospital, Gorakhpur, India with the chief complaint of swelling over right side of face, for the past three years. She was referred to the Department of Laboratory Medicine for FNAC.

While taking history of this case, the patient said that the swelling was painless, and initially smaller in size which gradually increased to the present size. She did not have any difficulty with speech and deglutition. The patient had taken homeopathic medication for the swelling for the past two years, but it did not reduce in size.

On systemic examination, the patient was healthy and there was no regional lymphadenopathy.

On extraoral examination, there was facial asymmetry due to swelling on the right side which was dome-shaped, 4x3 cms with smooth surface and was present on the right cheek region.

On bimanual palpation the mass could be felt between buccal mucosa and skin, and it was not fixed to the deeper structures. Mouth opening was adequate and there were no signs of motor or neurosensory deficit in the region of the lesion

CT scan of face was suggestive of well-defined encapsulated homogeneously enhancing lesion in the right buccal space region without invasion of the adjacent structures. Differential diagnosis of the lesion included minor salivary gland tumour, tumour of accessory parotid salivary gland, lipoma and neurofibroma.

After explaining about the FNAC procedure and taking consent from the patient, the FNAC was performed using a 23-gauge needle, with a 10 ml syringe. The blood mixed particulate material was aspirated. Both airdried and alcohol-fixed smears were made for MGG and haematoxylin and eosin stains.

The smears were cellular and showed dual cell population composed of ductal cells and myoepithelial cells in small cohesive clusters with few plasmacytoid cells, spindle shaped cells in a background of abundant fibrillary chondroid myxoid ground substance and was cytologically diagnosed pleomorphic adenoma.

The patient underwent for surgery. Excisional biopsy specimen revealed a soft circumscribed encapsulated mass measuring 4.0 cm x 3 cm x 1.5 cm in size, tan in colour, and was firm in consistency. Cut section was firm, tan and exhibited some gelatinous areas and foci of calcification.

Histopathology revealed an encapsulated mass composed of tubules, clusters, and anastomosing trabeculae of epithelial cells with foci of myxoid and myxochondroid areas. Eosinophilic secretions were noted in some of the tubules. No significant atypia or increase in mitosis was noted. Lymphocytic cell infiltration was seen at periphery. Foci of cystic change was present. This confirmed the diagnosis of PA of salivary gland. Because the tumour was not associated with the parotid duct or gland, it was considered to be of buccal minor salivary gland origin. The patient was advised for a follow up.

PA of buccal minor salivary glands is a very rare occurrence both in adults and children. In this case of PA of buccal minor salivary gland the patient was successfully treated by wide local surgical excision, and aftera follow-up period of one year there was no recurrence.

PLEOMORPHIC ADENOMA- a brief review...

What is Pleomorphic adenoma (PA)?

It is a benign mixed tumour composed of epithelial and myoepithelial cells arranged in various morphological patterns, demarcated from the surrounding tissues by a fibrous capsule.

What are the common sites of occurrence of PA ?

• The most common sites for PA are salivary glands. Most commonly involved are major salivary glands -

• Parotid gland(84% ); Submandibular gland(8%) and minor salivary glands (6.5%).

• Among minor salivary glands, palate is the most commonly affected site followed by lips, cheeks, gingiva, floor of the mouth, tongue, tonsil, pharynx, retromolar area, and nasal cavity.

What is the age and sex predilection for PA?

It usually occurs in the fourth to sixth decades of life and is found more commonly in women than in men.

What is the gross appearance of PA?

PA usually presents as a mobile slowly growing, painless, firm, lobulated swelling.These benign neoplasms are usually well circumscribed and round or oval in shape. They vary in consistency from soft and fluctuant to firm and rubbery, depending on the presence of cystic or mucoid degeneration or the formation of chondroid or osteoid tissues. The size of the tumour varies from 1 to 7 cm in diameter.

What imaging studies and investigations should be done for diagnosis?

CT scan, MRI, and ultrasonography are useful in determining the size and extent of lesions and in determining the bone involvement.

Incisional biopsy of PA in situ may predispose to recurrence and it is contraindicated.

Fine needle aspiration cytology is the preferred diagnostic modality.

What are the histological types for PA?

PA has three histological subtypes: Myxoid (80% stroma), Cellular (myoepithelial cells predominating), and Mixed (classic). Histologically, they have epithelial and mesenchymal elements.

Epithelial cells are arranged in cord-like and duct-like cell patterns, along with areas of squamous metaplasia. The intercellular matrix shows fibrous, hyaline, myxoid, cartilaginous, and osseous areas. Myoepithelial cells are responsible for such pleomorphic extracellular matrix production.

In the minor glands, lesions are often more solid or cellular than those seen in the major glands, and the myoepithelial cells are often polygonal with a pale eosinophilic cytoplasm giving an epithelioid or plasmacytoid phenotype.

What is the Immunohistochemistry profile for PA?

Ductal (epithelial) cells are typically positive for cytokeratins (e.g. AE1 / AE3, CAM5.2 and CK7)

Myoepithelial cells are positive for GFAP, S100, SOX10, actin - alpha smooth muscle, calponin, p40 and p63

PLAG1 and HMGA2 can be used as surrogate immunohistochemical markers for underlying PLAG1 or HMGA2 fusion.

What is treatment for PA?

Surgical excision with an adequate margin of normal surrounding tissue is the treatment of choice for PA.

Ra­diotherapy is not indicated due to the radioresistant nature of the tumour.

What is the prognosis?

Inadequate resection, rupture of the capsule, or tumour spillage during excision can lead to local recurrence as these tumours often have microscopic pseudopod-like extensions into the surrounding tissues through the capsule.

Spiro et al. reported a recurrence in 7% of 1,342 patients with benign parotid neoplasms, and in 6% of patients with benign minor salivary gland tumours.

In few cases PA of minor salivary glands can undergo malignant transformation into carcinoma for example PA and metastasizing benign mixed tumour.

Recurrence after many years of surgical excision as well as malignant transformation is a concern, hence long-term follow-up of up to 10 years is necessary.

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