[Nuclear magnetic resonance tomography in the diagnosis of parotid tumors. A comparison of methods].

The diagnostic value and the limitations of magnetic resonance imaging (MRI) in the management of large parotid masses were evaluated in a prospective clinical study. The results were compared with computed tomography (CT) and B-mode ultrasonography (US). MRI was performed using a Siemens 1.5 Tesla Magnetom with a RF head coil and surface RF coils. The images were evaluated by the following parameters of clinical importance: tumour detectability and marginal appearance, internal architecture, regional extension, and artifact degradation. MR imaging of parotid masses was superior to CT and US for the following reasons. The marginal appearance of the tumour was sharp and further enhanced in T2 weighted pictures. The extension of the tumour can be well seen by use of transaxial and frontal projections. This is an advantage especially when the mass extends to the retromandibular fossa or even to the pterygopalatine fossa. The position of the jaw, external ear canal, mastoid, skull base, and vessels of the neck are clearly shown without artifact degradation. Benign neoplasms can be well differentiated from malignant tumours which show local infiltration into the adjacent anatomical structures as well as irregularities of their internal structure. However, their appearance in MRI can be identical to that of an acute inflammation of the parotid gland. In summary MRI is the imaging technique of choice for extensive parotid masses, whereas US is effective for small tumours not situated in the retromandibular fossa.