These tumours usually occur in older patients (6th to 8th decade), who have had a pleomorphic adenoma in situ for many years (typically 10-15 years) 1.
Patients will describe having had a stable parotid mass for many years, before experiencing rapid growth, often associated with painful facial nerve palsy due to tumour infiltration 1.
As these tumours are aggressive and infiltrating, they present as irregular masses extending into the gland parenchyma and beyond.
- T1: heterogeneous signal due to haemorrhage, necrosis and calcification 1
- T2: heterogeneous but generally low signal
- ADC: low values (compared to pleomorphic adenomas which typically have elevated values)
For staging see malignant salivary tumour staging.
Treatment and prognosis
These tumours have a high rate of metastasis at the time of diagnosis (25-76%) typically to brain, bone, lungs and of course local lymph nodes 2.
The differential is essentially that of other malignant salivary gland tumours including:
- 1. 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]
- 2. 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]