Pleomorphic adenoma
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]
Synonyms and keywords: Pleomorphic adenoma of the salivary glands; BMT; Benign mixed tumors of the salivary gland
Overview
Pleomorphic adenoma (also known as "Benign mixed tumor of the salivary gland") is a benign neoplastic tumor of the salivary glands. Pleomorphic adenoma is the most common type of salivary gland tumor and the most common tumor of the parotid gland.[1] Pleomorphic adenoma was first described by Beahrs in 1957.[2] Pleomorphic adenoma may be classified according to anatomical distribution into 4 groups: parotid gland pleomorphic adenoma, submandibular gland pleomorphic adenoma, minor salivary gland pleomorphic adenoma, and sublingual gland pleomorphic adenoma. The pathogenesis of pleomorphic adenoma is characterized by an admixture of polygonal epithelial and spindle-shaped myoepithelial elements. The mutation on PLAG1 gene has been associated with the development of pleomorphic adenoma. Pleomorphic adenoma is common and it accounts for 60% of all parotid gland tumors (represents 45-75% of all salivary gland neoplasms). The incidence of pleomorphic adenoma is approximately 2-3.5 per 100,000 individuals worldwide. The most important clinical feature of pleomorphic adenoma is a painless single-nodular parotid mass. Pleomorphic adenoma may be initially asymptomatic. Common symptoms of pleomorphic adenoma, may include: dry mouth, dysphagia, and painful chewing. MRI is the imaging modality of choice for pleomorphic adenoma. Surgical excision in conjunction with pre-surgical biopsy is the most common approach to the treatment of pleomorphic adenoma. The recurrence rate after surgery will depend on the histological subtype (mixed pleomorphic adenomas have a higher recurrence rate). In some cases, patients with pleomorphic adenoma can receive medications to stimulate saliva production, such as pilocarpin and cevimeline.
Historical Perspective
- Pleomorphic adenoma was first described by Beahrs in 1957.[2]
Classification
- Pleomorphic adenoma may be classified according to anatomical distribution into 4 groups:[3]
- Parotid gland pleomorphic adenoma
- Superficial lobe pleomorphic adenoma (most common)
- Submandibular gland pleomorphic adenoma
- Minor salivary gland pleomorphic adenoma
- Sublingual gland pleomorphic adenoma
- Pleomorphic adenoma may also be classified according to histological type into 3 subtypes:[3]
- Mixed (hypocellular)(most common)
- Cellular
- Classic
- Other variants of pleomorphic adenoma, include: lacrimal gland pleomorphic adenoma, where they account for approximately 50% of lacrimal gland tumors.
Pathophysiology
- The pathogenesis of pleomorphic adenoma is characterized by an admixture of polygonal epithelial and spindle-shaped myoepithelial elements.
- Pleomorphic adenoma is commonly located in the parotid gland (80%).
- The mutation on PLAG1 gene has been associated with the development of pleomorphic adenoma.
- On gross pathology, characteristic findings of pleomorphic adenoma, include:
- May have cartilaginous appearance
- Typically well-circumscribed
- Tumor is usually enveloped by a fibrous capsule
- On microscopic histopathological analysis, characteristic findings of pleomorphic adenoma, include:
- Mixture of epithelial and myoepithelial elements
- Background stroma that may be mucoid, mixed, cartilaginous or hyaline
- Epithelial elements may be arranged in duct-like structures, sheets, clumps and/or interlacing strands
- Epithelial elements consist of polygonal, spindle or stellate-shaped cells (hence pleomorphism)
- On inmunohistochemistry, characteristic findings of pleomorphic adenoma, include:
- Positive S-100
- Positive SMA
- Positive GFAP
Causes
- There are no established causes for pleomorphic adenoma.
Differentiating Pleomorphic Adenoma from Other Diseases
- Pleomorphic adenoma must be differentiated from other diseases that cause dry-mouth, single-nodular parotid mass, and dysphagia, such as:
- Warthin tumor
- Mucoepidermoid carcinoma
- Myoepithelioma
- Adenoid cystic carcinoma
Epidemiology and Demographics
- Pleomorphic adenoma is common
- Pleomorphic adenoma accounts for 60% of all parotid gland tumors, and it represents 45-75% of all salivary gland neoplasms.
- The incidence of pleomorphic adenoma is approximately 2-3.5 per 100,000 individuals worldwide.
Age
- Pleomorphic adenoma is more commonly observed among patients aged 60 to 70 years old.
- Pleomorphic adenoma is less commonly observed in children.
- Pleomorphic adenoma is more commonly observed among elderly and adult patients.
Gender
- Pleomorphic adenoma affects men and women equally.
Race
- There is no racial predilection for pleomorphic adenoma.
Risk Factors
- Common risk factors in the development of pleomorphic adenoma, include:[4]
- Ionizing radiation
- Occupations associated with an increased risk, such as:
- Rubber products manufacturing
- Asbestos mining
- Plumbing
- Some types of woodworking
Natural History, Complications and Prognosis
- The majority of patients with pleomorphic adenoma remain asymptomatic for years.
- Early clinical features include dry mouth, difficulty swallowing, and a palpable single nodular mass.
- If left untreated, patients with pleomorphic adenoma may progress to develop malignant transformation.
- Common complications of pleomorphic adenoma, include:[3]
- Nerve injury
- Cosmetic deformity
- Hemorrhage or hematoma
- Frey syndrome
- If there is a malignant transformation, prognosis is generally poor, and the 5-year survival rate of patients with pleomorphic adenoma is approximately 30%.[3]
Diagnosis
Symptoms
- Pleomorphic adenoma may be initially asymptomatic.
- Symptoms of pleomorphic adenoma may include the following:[3]
Physical Examination
- Patients with pleomorphic adenoma may appear with a facial deformity.
- Physical examination of head and neck, may be remarkable for:[5]
- Submandibular single, mobile, painless, and firm nodular mass
- Eversion of the ear lobe
- Limited mandible motion
Laboratory Findings
- There are no specific laboratory findings associated with pleomorphic adenoma.[3]
Imaging Findings
- MRI is the imaging modality of choice for pleomorphic adenoma.[5]
- On CT, characteristic findings of pleomorphic adenoma, include:
- Smooth, and well-marginated tumors
- The attenuation values of the mass are usually homogeneous and higher than that of the surrounding gland
- Tumor enhancement is variable and can result in a missed diagnosis if delayed images are not acquired
- Pleomorphic adenomas are poorly enhancing in the early phase of contrast enhancement, though the amount of enhancement increases over time).
- On MRI, characteristic findings of pleomorphic adenoma, include:[5]
- Pleomorphic adenomas are usually well-circumscribed
- Homogeneous masses with low intensity on T1-weighted images and high intensity on T2-weighted images.
- They commonly have a rim of decreased signal intensity on T2-weighted images.
- After gadolinium enhancement, the tumors are homogeneously enhancing unless they are large.
Gallery
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MRI: A right parotid pleomorphic adenoma Images courtesy of RadsWiki -
MRI: A right parotid pleomorphic adenoma Images courtesy of RadsWiki -
MRI: A right parotid pleomorphic adenoma Images courtesy of RadsWiki -
MRI: A right parotid pleomorphic adenoma Images courtesy of RadsWiki -
MRI: A right parotid pleomorphic adenoma Images courtesy of RadsWiki -
PET: A right parotid pleomorphic adenoma Images courtesy of RadsWiki
Other Diagnostic Studies
- Pleomorphic adenoma may also be diagnosed using fine needle aspiration (FNA) and core needle biopsy.
- Findings on fine needle aspiration (FNA) and core needle biopsy, include:
- Admixture of polygonal epithelial and spindle-shaped myoepithelial elements
- Mesenchymal stroma (important feature)
- Proliferation of myoepithelium and epithelium
Treatment
Medical Therapy
- There is no treatment for pleomorphic adenoma; the mainstay of therapy is surgery.
- In some cases, patients with pleomorphic adenoma can receive medications to stimulate saliva production, such as:
- Pilocarpine
- Cevimeline
Surgery
- Surgery is the mainstay of therapy for pleomorphic adenoma.
- Surgical excision in conjunction with pre-surgical biopsy is the most common approach to the treatment of pleomorphic adenoma.
- The recurrence rate after surgery will depend on the histological subtype.
- Mixed pleomorphic adenomas have a higher recurrence rate.
Prevention
- There are no primary preventive measures available for pleomorphic adenoma.
- Once diagnosed and successfully treated, patients with pleomorphic adenoma are followed-up every 6 or 12 months.
References
- ↑ Ewa J. Bialek, Wieslaw Jakubowski, Piotr Zajkowski, Kazimierz T. Szopinski, and Antoni Osmolski. US of the Major Salivary Glands: Anatomy and Spatial Relationships, Pathologic Conditions, and Pitfalls. RadioGraphics 2006 26: 745-763.
- ↑ 2.0 2.1 Keerthi R, Raut RP, Vaibhav N, Ghosh A (2014). "Carcinoma ex pleomorphic adenoma: Diagnostic dilemma and treatment protocol". Indian J Dent. 5 (3): 157–60. doi:10.4103/0975-962X.140840. PMC 4213878. PMID 25565746.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Pleomorphic adenoma. Wikipedia. https://en.wikipedia.org/wiki/Pleomorphic_adenoma. Accessed on April 25, 2016
- ↑ Pleomorphic adenoma. Salivary Gland Cancer Treatment–for health professionals (PDQ®).http://www.cancer.gov/types/head-and-neck/hp/salivary-gland-treatment-pdq#link/_403_toc Accessed on February 17, 2016
- ↑ 5.0 5.1 5.2 Pleomorphic adenoma. Radiopedia. http://radiopaedia.org/cases/pleomorphic-adenoma-9 Accesed on April 28, 2016