Clinical History
Slow growing, non tender, non painful mass of the left retromandibular region in an adult male patient.
Imaging Findings
The patient complained of a slowly growing mass of the left retromandibular region. At the clinical examination the mass appeared solid, well circumscribed, not tender or painful. An US examination
was performed, which showed a hypoechoic, well defined mass, with intranodular vascularization at color Doppler examination., located in the left parotid gland. No other significant findings were
observed, and the US diagnosis was that of a pleomorphic adenoma of the left parotid gland. The patient underwent a neck MR examination, then undewent surgery for excision of the mass.
Discussion
The pleomorphic adenoma is the most common benign salivary gland tumor, accounting for as many as 80% of all such tumors and it is also the most common benign parotid gland tumor (about 85%). It is
histologically composed of 2 subtypes of cells: epithelial and mesenchymal. These tumors are typically well demarcated from the surrounding tissue by a fibrous capsule, variable in thickness and
completeness. These lesions have been reported to contain small protrusions (pseudopodia) extending beyond the central mass, caused by variability in the growth rates of the various cell types. This
factor contributes to recurrence rates as high as 50%, depending on the type of surgical intervention. Most parotideal pleomorphic adenomas are confined to the superficial lobe, but they can
occasionally arise in the deep lobe. Women are predominantly affected, with a ratio of 3:2; the typical age of occurrence is between the fourth and sixth decades. Parotid pleomorphic adenomas usually
arise as a slow-growing, firm, slightly compressible parotid mass. Almost all are asymptomatic, and they are usually brought to the attention when routine physical examination is performed or when
the patient feels or sees a parotid mass. Differential diagnosis (1) is with malignant parotid tumors, and with other conditions such as sarcoidosis, lymphoma, lymphadenopathy. The MR expected
characteristic appearances (2) of pleomorphic adenomas are usually of a well-circumscribed, homogeneous mass hypointense on T1 images and hyperintense on T2 (these two features are present in the
case shown), with the fibrous capsule forming a hypointense rim on T2-weighted and fat-suppressed T1, usually showing homogeneous contrast enhancement after gadolinium, and areas less enhancement in
larger masses (as in Figure 2). When it becomes large, the tumor may have areas of fibrosis, necrosis, and hemorrhage (visible in Figure 1), with inhomogeneous signal intensity apparent in these
cases. Lobulation is commonly visualized and is also suggestive of the diagnosis. Special attention should be paid to any possible invasion into adjacent soft tissues. All pleomorphic adenomas should
be surgically removed because the risk of malignancy if untreated, with an adequate margin of grossly normal surrounding tissue needed to prevent local recurrence due to microscopic pseudopod-like
extensions into the surrounding tissue, due to "dehiscences" in the false capsule (3). Spiro (4) reported a recurrence in 7% of 1342 patients with benign parotid neoplasms and 6% of patients with
benign minor salivary gland tumours. In our case the surgeon felt confident enough to proceed to enucleation of the tumor, without parotideal resection. Malignant degeneration, most commonly to
carcinoma, is relatively rare and has been reported to occur in 2-7% of untreated cases. In rare cases, pleomorphic adenomas degenerate into a true malignant mixed tumor and a metastasizing benign
mixed tumor (5). In this case the surgon opted for enucleation instead of rescission of larger surgical margins, to have a shorter time in general anesthesia for the patient, who suffered an unstable
cardiac condition.
Differential Diagnosis List
Pleomorhic adenoma of the left parotid gland.
Final Diagnosis
Pleomorhic adenoma of the left parotid gland.
