Imaging diagnosis of salivary gland tumor

Abstract

The histopathological diagnosis of salivary gland tumors is sometimes difficult, because the tumors have various histologic patterns and manifold tissue components coexist in a histologic pattern. Therefore, the differential imaging diagnosis of a benign and malignant tumor in the salivary gland is also sometimes difficult.
A salivary gland lesion in which the border is slightly unclear is sometimes a malignant tumor, even though the borderline looks almost clear on the images. Therefore, in the imaging diagnosis of salivary gland tumors, the clearness of the boundary on the images is very important and its cautious interpretation is essential; the clearness should be judged not by CT but by ultrasonography and MRI. Moreover, the CT and MRI images should be observed by optimal indication on a DICOM Viewer, if possible.
Regarding major salivary gland tumors: over 70% of parotid gland tumors are benign, 40% of submandibular gland tumors are malignant, and 80% of sublingual tumors are malignant. These figures are important when interpreting diagnostic images of major salivary gland tumors. A parotid gland tumor in which the border is not always clear should be suspected as malignant. A lesion that is confirmed as a sublingual gland tumor on diagnostic images should be diagnosed as a malignant tumor.
Concerning minor salivary gland tumors: when the tumor is small, a borderline is often clear even though the tumor is malignant. Hence, imaging findings of a lesion with a clear boundary are not evidence of a benign tumor in the minor salivary gland. In malignant salivary gland tumors of the palatal region, particular attention should be paid to weak bone invasion, which cannot be detected on imaging findings. In the lip and buccal region, ultrasonography is the most effective imaging modality. It is necessary to remember that mucoepidermoid carcinoma occurs also in the jawbones.