Tumours of the oropharynx and oral cavity: perineural spread and bone invasion.

Clinical examination of the oral cavity and oropharynx provides essential information in the assessment of neoplastic lesions. A precise evaluation of their deep spread along the most common growth pathways can be achieved by imaging, ranging from the basic, but nowadays incomplete, information of conventional X-ray, to the sophisticated details obtained by MR. Three oncological questions must be faced: the three dimensional evaluation of primary tumour spread; the assessment of nodal involvement; the post-treatment survey with the early detection of local recurrences, during the follow up. Either CT or MR accurately assesses the deep extension of neoplasms, nevertheless, the most cost-effective protocol is provided by a combination of CT and ultrasound (staging respectively T and N). MR is the technique of first choice when an infiltration of the base of the tongue or perineural spread is suspected, because of its superior ability to detect muscular invasion and segmental abnormalities of cranial nerves. Bone involvement can be adequately showed by MR not only because focal erosions of the cortical rim are well demonstrated, but also by means of the early demonstration of bone marrow abnormalities. Moreover, MR plays an essential role during the follow up, as it is the only morphological imaging technique permitting to differentiate recurrent tumour and necrosis from scar tissue.