Pleomorphic Adenoma


Article Author:
Maria Bokhari


Article Editor:
Joshua Greene


Editors In Chief:
James Beauchamp
Mark Pellegrini
Nicole Hale-Crutch


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Kyle Blair
Trevor Nezwek
Radia Jamil
Erin Hughes
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Navid Mahabadi
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Daniyal Ameen
Altif Muneeb
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes
Komal Shaheen
Sandeep Sekhon


Updated:
1/19/2019 2:08:48 PM

Introduction

Pleomorphic adenoma, the most common salivary gland tumor, is also known as benign mixed tumors (BMT's), because of its dual origin from epithelial and myoepithelial elements.It is the commonest of all salivary gland tumors constituting up to two-thirds of all salivary gland tumors.[1][2][3]

Etiology

The etiology of pleomorphic adenoma is unknown, but the incidence of this tumor has been increasing in the last 15-20 years in relation to the exposure of radiation. One study suggests that oncogenic simian virus (SV40) may play a role in the onset or progression of pleomorphic adenoma.  Prior head and neck irradiation is also a risk factor for the development of these tumors. [4]

Epidemiology

Pleomorphic adenoma is the most common benign salivary gland neoplasm. In most studies, it represents 45-75% of all salivary gland tumors; the annual incidence is approximately two to three and a half cases per 100,000 population. Pleomorphic adenoma occurs in individuals of all ages; however, it is most common in the third to sixth decades. Pleomorphic adenoma incidence is slightly more in females than in males (2:1 ratio). Pleomorphic adenomas account for 70-80% of benign salivary gland tumors and are especially common in the parotid gland. [5]Pleomorphic adenoma predominantly affects superficial lobe of the parotid gland. Distribution among the various salivary glands is as follows: 

  • Parotid gland: 84% 
  • Submandibular gland: 8%
  • Minor salivary glands: 6.5% 

Pathophysiology

Microscopically pleomorphic adenoma has a highly variable appearance, hence the name pleomorphic. It is characterized by mixed proliferation of polygonal epithelial and spindle-shaped myoepithelial cells in a variable stroma matrix of mucoid, myxoid, cartilaginous or hyaline origin. Epithelial elements are usually of polygonal, spindle or stellate-shaped cells which may be arranged to form duct-like structures, sheets, clumps,  or interlacing strands. The ducts and tubules are seen usually exhibiting an outer lining in addition to an inner cuboidal epithelial cell layer. This is outer myoepithelial cell layer (or layers) which merges into the surrounding stroma which also contains dispersed or clumped myoepithelial element cells. Areas of squamous metaplasia and epithelial pearls can be found. The tumor lacks the true capsule and is surrounded by a fibrous pseudo capsule of variable thickness. The tumor extends through normal glandular parenchyma in the form of finger-like pseudopodia. These microscopic extensions account for the high risk of recurrence in cases treated with simple enucleation or surgical resections performed with inadequate surgical margins.

Histopathology

Histology will reveal proliferation of myoepithelial and epithelial cells of the ducts. There is also a marked increase in stromal components. The tumor is usually not well encapsulated.

History and Physical

Pleomorphic adenoma mostly presents as a  solitary mobile slow-growing, painless mass, which may be present for many years. Symptoms and signs mainly depend on size, location, and potential to undergo malignant transformation. In the parotid gland, signs of facial nerve weakness occur when the tumor is large or if it undergoes malignant change. Pleomorphic adenoma in the deep lobe of the parotid gland may present as an oral retro tonsillar or para-pharyngeal mass which is visible or usually palpable. Rapid enlargement of a tumor nodule should raise a concern of malignant change. Minor salivary gland tumors may present with a variety of symptoms, including dysphagia, hoarseness,  dyspnea, difficulty in chewing, and epistaxis dependent on the site of the tumor.

Evaluation

The diagnosis is made both on tissue sampling and radiographic studies. Tissue sampling procedures including fine needle aspiration (FNA) and core needle biopsy which can be done in an outpatient setting. These procedures are associated with very low tumor seeding rates.[6][7]

FNA can determine whether the tumor is malignant in nature with an approximate sensitivity of 90%. Core needle biopsy is more invasive but provides more accurate histological typing of the tumor with a diagnostic accuracy of around 97%. Immunohistochemistry may prove to be supportive in delineating the different cell components.

CT examination a pleomorphic adenoma usually appears as smoothly marginated or lobulated homogeneous soft tissue density globular mass. Necrosis can be seen in larger masses. Few foci of calcification are common. Smaller tumors show early homogenous prominent enhancement while in the case of larger tumors enhancement is less marked and delayed.

MRI is similar to CT; smaller masses appear well-circumscribed and homogeneous whereas larger tumors appear heterogeneous.

  • T1: usually of low intensity.
  • T2: usually of very high intensity (especially myxoid type) 6 often have a rim of decreased signal intensity on T2-weighted images representing the surrounding fibrous capsule.
  • T1 C+ (Gd): usually demonstrates homogeneous enhancement. 
  • The presence of either T2 hypointensity or ill-defined margins after contrast administration can be a simple MR imaging malignancy test for parotid tumors, with a sensitivity and specificity of 0.70 and 0.73, respectively.
  • Post contrast STIR images help the delineate the perineural spread of tumor in case of malignant change.

Ultrasound pleomorphic adenomas characteristically appear hypoechoic in texture.  They usually show a lobulated distinct border with or without posterior acoustic enhancement. Ultrasound guided biopsy or FNA are minimally invasive and cost effective procedures. 

Angiography (DSA) can also be considered.

Treatment / Management

Previously carried out enucleation procedure has been abandoned because of high associated rates of recurrence. Presently pleomorphic adenoma of the parotid gland is treated either with superficial (Patey's operation) or total parotidectomy with the latter being the more frequently performed procedure due to lower incidence of recurrence. Meticulous technique is required to preserve the facial nerve. The tumors of the submandibular glands are treated with simple excision procedure with preservation of adjacent nerve including the mandibular branch of the trigeminal nerve, the hypoglossal nerve, and the lingual nerve.[8]

When in the minor salivary glands, a five mm margin should be obtained. These tumors do not invade into periosteum. Thus, the bone need not be resected. When tumor bed recurrences occur, they show significant resistance to treatment, with management options including monitoring only, surgery, and radiotherapy.

Pleomorphic adenomas harbor a small risk of malignant transformation. The malignant potential is proportional to the time the lesion is in situ (1.5% in the first five years, 9.5% after 15 years). Therefore, excision is warranted in almost all cases. Other risk factors for malignancy include advanced age, radiation therapy, large size, and recurrent tumors.

Differential Diagnosis

Differentials for pleomorphic adenoma include Warthin tumor, parotid nodal metastasis, facial nerve schwannomas, myoepitheliomas, mucoepidermoid and adenoid cystic carcinoma, and a large variety of other neoplasms nonspecific to salivary glands. Histopathology remains the gold standard in differentiating them all.

Enhancing Healthcare Team Outcomes

Pleomorphic adenoma of the parotid gland is not a common lesion. However, the majority of patients present to the primary care provider with complaints of a painless mass on the side of the face. Thus, primary care providers and nurse practitioners should have some idea about the differential diagnosis of such lesions and make appropriate referrals. The ideal treatment for pleomorphic adenomas is surgical excision. Even though the lesion is benign, there is a reported recurrence rate of 7-15%. All patients who undergo excision of this lesion need to be informed about the potential for facial nerve injury, which can occur if the tumor is in close proximity of the nerve. If the facial nerve is injured, the patient must be taught an eye care program and how to use lubricating drops to prevent keratopathy. A referral to an ophthalmologist is highly recommended. Depending on the severity of nerve injury, it may take months or years to fully recover eyelid function. [9](Level V)


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Pleomorphic Adenoma - Questions

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What is the most common type of parotid tumor?



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A 51-year-old man presents with a 6-month history of a slowly enlarging 2-cm mass in the tail of the parotid gland. He denied any symptoms. He underwent a superficial parotidectomy. What is the most probable histopathologic diagnosis of this mass?



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A 56 year old female is found to have painless, unilateral, slow growing tumor of the parotid gland. What is the best treatment?



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A 52 year old male presents with a slowly growing mass of the hard palate. It is asymptomatic and measures 0.75 x 0.75 cm. No other abnormalities are found. Needle biopsy shows a pleomorphic adenoma. Select the best management.



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What neoplasm is the most common in the parotid gland?



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Which of these is a risk factor for pleomorphic adenoma?



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A 49-year-old female presents with complaints of a mass just below her ear. She noticed it this past weekend while showering. She denies any trauma and is on no medications. On exam, the mass is firm but feels irregular on the surface. A fine needle aspiration biopsy is read as pleomorphic adenoma. Which of the following is considered to be a risk factor for this malignancy?



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Pleomorphic Adenoma - References

References

Mc Loughlin L,Gillanders SL,Smith S,Young O, The role of adjuvant radiotherapy in management of recurrent pleomorphic adenoma of the parotid gland: a systematic review. European archives of oto-rhino-laryngology : official journal of the European Federation of Oto-Rhino-Laryngological Societies (EUFOS) : affiliated with the German Society for Oto-Rhino-Laryngology - Head and Neck Surgery. 2018 Nov 13     [PubMed]
Lee JH,Kang HJ,Yoo CW,Park WS,Ryu JS,Jung YS,Choi SW,Park JY,Han N, PLAG1, SOX10, and Myb Expression in Benign and Malignant Salivary Gland Neoplasms. Journal of pathology and translational medicine. 2018 Nov 14     [PubMed]
Meshram GG,Kaur N,Hura KS, Pediatric Pleomorphic Adenoma of the Parotid: Case Report, Review of Literature and Novel Therapeutic Targets. Children (Basel, Switzerland). 2018 Sep 18     [PubMed]
Gündüz AK,Yeşiltaş YS,Shields CL, Overview of benign and malignant lacrimal gland tumors. Current opinion in ophthalmology. 2018 Sep     [PubMed]
Zhan KY,Khaja SF,Flack AB,Day TA, Benign Parotid Tumors. Otolaryngologic clinics of North America. 2016 Apr     [PubMed]
Kato H,Kawaguchi M,Ando T,Mizuta K,Aoki M,Matsuo M, Pleomorphic adenoma of salivary glands: common and uncommon CT and MR imaging features. Japanese journal of radiology. 2018 Aug     [PubMed]
Shalley S,Chand N,Aggarwal A,Garg LN,Yadav V,Yadav A, Diagnostic Accuracy of Fine Needle Aspiration Cytology in Lesions of Oral Cavity and Salivary Glands: A Clinico-Pathological Study. The open dentistry journal. 2018     [PubMed]
Gleave EN,Whittaker JS,Nicholson A, Salivary tumours--experience over thirty years. Clinical otolaryngology and allied sciences. 1979 Aug     [PubMed]
Infante-Cossio P,Gonzalez-Cardero E,Garcia-Perla-Garcia A,Montes-Latorre E,Gutierrez-Perez JL,Prats-Golczer VE, Complications after superficial parotidectomy for pleomorphic adenoma. Medicina oral, patologia oral y cirugia bucal. 2018 Jul 1     [PubMed]

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