Carcinoma ex-pleomorphic adenoma of parotid
Left parotid mass
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A 28 mm x 22.5 mm x 40 mm heterogenously enhancing mass lesion involving the deep lobe of the left parotid is demonstrated. The lesion demonstrates areas of high signal on T2WI and marked restricted diffusion. Although the mass lesion contacts the left mandibular angle, the mandibular cortex and marrow signal is preserved.
There is no abnormal perineural enhancement. Moderately enlarged left-sided level II lymph nodes noted as well as a left retro-pharyngeal lymph node, measuring up to 6.5 mm. Minimally enlarged right-sided level II lymph nodes noted, likely inflammatory.
There is a right rim-enhancing, cyst-like lesion with internally restricting content within the right glosso-tonsillar sulcus, possibly representing a retention cyst.
Intracranially, there is an established (likely previously hemorrhagic) infarct within the left external capsule. The well-rounded cyst-like lesion closely associated with the right anterior commissure, likely representing a prominent perivascular space or an established lacunar infarct.
The heterogenous mass lesion within the deep lobe of left parotid likely represents a malignant lesion.
There is no associated peri-neural tumor spread, however, the ipsilateral level II lymph nodes are enlarged.
Sectioning reveals a large, well-circumscribed, partly encapsulated, pale white tumour 33x24x24mm with areas of necrosis and cystic formation. The tumour is situated 1mm from the medial, posterior and superior margins, 8mm from the lateral margin and >10mm from the anterior and inferior margins. There is a segment of bone at the inferomedial aspect 35x15x12mm with no macroscopic evidence of tumour involvement.
Sections of parotid gland show a salivary duct carcinoma with evidence of intermixed pleomorphic adenoma (carcinoma ex pleomorphic adenoma). Invasive carcinoma is well-circumscribed with a pushing border. The tumour cells demonstrate a squamoid appearance with abundant cytoplasm and form large dilated ducts containing central comedonecrosis. Areas of chondromyxoid stroma with loosely arranged spindled and epithlioid cells represent the residual pleomorphic adenoma component.
Immunohistochemical results show tumour cells stain Her-2+, Androgen Receptor+, GCDFP+ and PSA-.
Completely excised salivary duct carcinoma arising from a pleomorphic adenoma (Carcinoma ex-pleomorphic adenoma), size 33mm with no bony, lymphovascular or perineural invasion. Negative lymph nodes.
Key learning points:
1. The imaging findings of heterogenous signal and irregular margins are not typical for a pleomorphic adenoma, which is the most common mass within the parotid. These findings suggest a malignant etiology.
2. Pleomorphic adenomata are usually surgically excised due to the small risk of malignant transformation.