eRadiograph Volume 7: Imaging of Oral Cavity | Page 226

gland are benign whereas in the sublingual gland only 15 – 20% are benign.
Tumors are classified into two types: epithelial those arising from glandular and
ductal epithelium; and non-epithelial those arising from other tissue elements such
as fat, lymph node, vascular and neural tissues.
Epithelial
PLEOMORPHIC ADENOMA:(PA)
This is the most common benign tumor of the major salivary glands (70 – 80%). 84%
of all pleomorphic adenoma arise in the parotid gland – They are termed pleomorphic
as they may contain glandular, ductal or solid components. These present as slow
growing painless tumors. 90% of these occur in the superficial portion of the parotid
gland. On CT they appear as well defined lobulated masses of higher density than
parotid gland parenchyma. Pleomorphic adenoma may have lobulated margins and
dystrophic calcification. Presence of dystrophic calcification is highly suggestive of PA.
Occasionally they may be cys tic, due to mucoid contents simulating a cyst on imaging
or appear heterogenous due to presence of necrosis and haemorrhage. All
pleomorphic adenoma enhance densely with IV contrast. The smaller lesions enhance
homogeneously whereas larger lesions enhance heterogeneously due to presence of
necrosis, haemorrhage, cystic change. On MRI these lesions are hypointense on
T1W1, hyperintense on T2W1. A hypointense capsule may be seen on T2WI. Larger
tumors may appear inhomogeneous due to the presence of necrosis/haemorrhage,
calcification/ ossification. Treatment is parotidectomy as recurrences may occur with
only enucleation, subsequently producing multiple daughter lesions.

On imaging these may appear as a focal aggressive mass within a pleomorphic
adenoma, or an aggressive mass with inhomogeneity.-necrosis, haemorrhage,
irregular and infiltrating margins. On MRI this malignant transformation may be seen
as a focal hypointense mass within T2 hyper intensity or replacement of T2
hyperintensity with hypointensity.
WARTHIN TUMOR:(WT)
THIS IS THE Second most common benign tumor arising in parotid gland constituting
4 –10% of all parotid tumors. These are slow growing cystic neoplasm arising from the
lower portion of the parotid gland (tail of parotid) over the angle of the mandible.

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Parotid Space

Pleomorphic adenomas if left untreated (25%) may turn malignant known as
carcinoma ex pleomorphic adenoma.This risk of malignancy change is usually related
to the tumour being present for a long duration. Malignant change may also occur in a
previously resected pleomorphic adenoma. Malignant change manifests as rapid
growth in a previously benign parotid mass generally associated with pain and facial
nerve paralysis. These may metastasize to lymph nodes, bone, brain and lung.