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Salivary glands » General
Pleomorphic Adenoma
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Presentation 52-year-old male patient with pain and bulging sensation in the right parotid region. A sonogram was requested.
 
 
Caption: Longitudinal sonogram of the right parotide gland.
Description: Longitudinal sonogram reveals a hypoechoic nodule, lobulated distinct border +/- posterior acoustic enhancement with through transmission.
 
 
Caption: Transverse sonogram of the right parotide gland.
Description: Transversal sonogram reveals a hypoechoic nodule, lobulated distinct border +/- posterior acoustic enhancement with through transmission.
 
 
Caption: Longitudinal sonogram of the right parotid gland.
Description: Longitudinal sonogram reveals a hypoechoic nodule, lobulated distinct border +/- posterior acoustic enhancement with through transmission. The color doppler shows low vascularization in its interior and peripheral flow with small branches that tend to radiate towards the center of the tumor.
 
 
Caption: Longitudinal sonogram of the right parotid gland.
Description: Longitudinal sonogram reveals a hypoechoic nodule, lobulated distinct border +/- posterior acoustic enhancement with through transmission. The power doppler shows low vascularization in its interior and peripheral flow with small branches that tend to radiate towards the center of the tumor.
 
Differential Diagnosis
When in the parotid gland consider:

- Warthin tumour.
- Mucoepidermoid carcinoma.
- Myoepithelioma.
- Adenoid cystic carcinoma. (ACC)
- Parotid nodal metastasis.
- Parotid non-Hodgkin lymphoma.
- Intraparotid facial nerve schwannoma.
 
Final Diagnosis Pleomorphic Adenoma
 
Discussion
Pleomorphic adenoma is a common benign salivary gland neoplasm characterised by neoplastic proliferation of parenchymatous glandular cells along with myoepithelial components, having a malignant potentiality.

It is the most common type of salivary gland tumor and the most common tumor of the parotid gland. It derives its name from the architectural Pleomorphism (variable appearance) seen by light microscopy. It is also known as "Mixed tumor, salivary gland type" (BMT's), which describes its pleomorphic appearance as opposed to its dual origin from epithelial and myoepithelial elements.

Pleomorphic adenomas account for 70-80% of benign salivary gland tumours and are especially common in the parotid gland (see below) 1,2. Patients are typically middle aged1, and prior head and neck irradiation is a risk factor for the development of these tumours.

The sonographic features are:

Although findings do depend on tumour size, in general, they are well circumscribed rounded masses, most commonly located within the parotid gland.

When they arise from the deep lobe of the parotid they can appear entirely extra parotid, seen in the parapharyngeal space, without a fat plane between it and the parotid, and widen the stylomandibular tunnel. Pleomorphic adenomas can also arise from salivary rest cells in the parapharyngeal space itself without connection to the parotid gland.

- Typically, hypoechoic. May show a lobulated distinct border +/-  posterior acoustic enhancement with through transmission3.
- It can be very hypoechogenic that confuse with a cyst (adjust gain). Use color Doppler to demonstrate solid nature1.
- Larger size adenomas (greater than 30mm) can suffer from cystic or hemorrhagic degeneration1.
- Dystrophic calcifications in long-evolving adenomas (overlap with findings of a malignant lesion), but without associated adenopathies3.
- Characterization of the adenoma by ultrasound: sensitivity 82%, specificity 86% and accuracy of 84%2.
- The Doppler pattern is variable, generally low vascularization is observed in its interior and peripheral flow with small branches that tend to radiate towards the center of the tumor (not pathognomonic). IR <0.8 and IP <1.8, suggest benignity3.
- Ultrasound is also useful in guiding a biopsy (both FNAC and core biopsies) but needs to be carried out with care to avoid facial nerve damage4,5.

Surgical excision is curative, however as the tumour is poorly encapsulated (despite imaging suggesting otherwise), there is a significant rate of recurrence in the tumour bed. Exact rates of recurrence vary widely depending on series and surgical technique (1-50%)1.

There is a small risk of malignant transformation into a carcinoma ex-pleomorphic adenoma which is proportional to the time the lesion is in situ (1.5% in first 5 years, 9.5% after 15 years), thus excision is recommended in essentially all cases. Additional risk factors for malignancy include advanced age, large size, radiation therapy and recurrent tumours2,6.
 
Case References
1. Thoeny HC. Imaging of salivary gland tumours. Cancer Imaging. 2007;7 : 52-62. doi:10.1102/1470-7330.2007.0008 - Free text at pubmed - Pubmed citation.
2. Moonis G, Patel P, Koshkareva Y et-al. Imaging characteristics of recurrent pleomorphic adenoma of the parotid gland. AJNR Am J Neuroradiol. 2007;28 (8): 1532-6. doi:10.3174/ajnr.A0598 - Pubmed citation.
3. Białek EJ, Jakubowski W, Karpińska G (Sep 2003). "Role of ultrasonography in diagnosis and differentiation of pleomorphic adenomas: work in progress". Arch Otolaryngol Head Neck Surg. 129 (9): 929–33. doi:10.1001/archotol.129.9.929. PMID 12975263.
4. Howlett DC, Menezes LJ, Lewis K et-al. Sonographically guided core biopsy of a parotid mass. AJR Am J Roentgenol. 2007;188 (1): 223-7. doi:10.2214/AJR.05.1549 - Pubmed citation.
5. Wan YL, Chan SC, Chen YL et-al. Ultrasonography-guided core-needle biopsy of parotid gland masses. AJNR Am J Neuroradiol. 2004;25 (9): 1608-12. AJNR Am J Neuroradiol (full text) - Pubmed citation.
6. Kato H, Kanematsu M, Mizuta K et-al. Carcinoma ex pleomorphic adenoma of the parotid gland: radiologic-pathologic correlation with MR imaging including diffusion-weighted imaging. AJNR Am J Neuroradiol. 2008;29 (5): 865-7. doi:10.3174/ajnr.A0974 - Pubmed citation
 
Technical Details
Ultrasound scanner. - Voluson 730 PRO. General Electric.
Transducer.- 10 - 12MHz linear array.
Scanning in both transverse and longitudinal planes.
 
Follow Up The patient underwent a biopsy, showing a pleomorphic adenoma. Then the tumor was removed.
 
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