Pleomorphic adenoma

General features:
Also known as benign mixed tumor
70-80% of all benign salivary tumors
Most occur in parotid gland (60%–90%)
90% superficial to facial nerve
40-60 yrs
More common in women
Usually solitary and unilateral
Slow growing painless mass
Most are in superficial lobe

Recurrence and malignant transformation:
Malignant transformation may occur - carcinoma ex pleomorphic adenoma (malignant mixed tumor), carcinosarcoma (true malignant mixed tumoe), metastasizing benign mixed tumor
If left untreated, 25 may undergo malignant transformation
Recurrence known to occur, more with enucleation
Recurrences - often multiple, around the original lesion (cluster of grapes)

US:
US shows round welldefined hypoechoic lobulated mass with posterior enhancement; May be heterogeneous or show cystic changes or calcification; May show peripheral, basket-like flow
USG used for FNA, FNAB or core biopsy

CT:
Smaller are homogeneous, well-defined, hyperattenuating (may be hypoattenuating or cystic)
Larger are illdefined, lobulated, heterogeneous due to necrosis and/or hemorrhage
Varibale mild enhancement
Dystrophic calcifications or ossifications - rarely seen - but highly suggestive of diagnosis
May be slightly illdefined, appearing aggressive - secondary to hemorrhage or surrounding inflammation

MR:
Low on T1, high on T2
Low signal capsule on T2, and fat sat post Gd T1 - often seen
Large ones may be heterogenous with various signals due to haemorrhage

Management:
Facial nerve–sparing partial parotidectomy
Often recur

Differentials:
Lymphnodal disease suggests malignancy
Low signal on T1 and T2 suggests malignancy in known pleomorphic adenoma
References:
1. Lowe LH et al. Swelling at the Angle of the Mandible: Imaging of the Pediatric Parotid Gland and Periparotid Region. Radiographics. 2001;21:1211-1227
2. BialekEJ etal. US of the Major Salivary Glands: Anatomy and Spatial Relationships, Pathologic Conditions, and Pitfalls. RadioGraphics 2006;26:745-763
3. Howlett DC. High resolution ultrasound assessment of the parotid gland.British Journal of Radiology (2003) 76, 271-277
4. Som PM and Curtin HD. Head and Neck Imaging. 4th Edition. Mosby