Familial Nasopharyngeal Carcinoma 6

318 B. O’Sullivan and E. Yudefined by three points: (1) the superior margin ofthe sternal end of the clavicle, (2) the superior marginof the lateral end of the clavicle, (3) the point wherethe neck meets the shoulder (Greene et al. 2002).As defined this would include caudal portions oflevels IV and VB. All cases with lymph nodes (wholeor part) in the fossa are considered as N3b. Such adivision is difficult to determine on cross-sectionalimaging and potentially may not be described universallyin this manner by radiologists in their interpretationof CT and MRI data sets. In essence, the SCF andthe N staging criteria depend greatly on clinical examination,especially palpation. Furthermore, it is alsodifficult to delineate the supracavicular regions formodern radiotherapy treatment planning, and instead,more conventional lymph node levels are oftenrequired in clinical trial protocols. Recent data suggestthat the N categorization system for NPC could beadapted to be consistent with the international consensusguidelines that are used for other head andneck disease sites (Ng et al. 2007; Mao et al. 2008), andthe traditional nomenclature would not longer beneeded. This would have practical value for diagnosticreporting, radiotherapy planning, and may well bemore consistent (Mao et al. 2008). While the actualterms used to describe low lying neck disease wouldchange if the international consensus guidelines fortopographic lymph node description were adopted, itwould neither change the NPC TNM neck classificationitself nor would it affect the stage grouping.24.5.3Base of Skull and Intracranial InvasionSkull base invasion is apparent in about one-third ofpatients with NPC (Roh et al. 2004) and cranial nervedysfunction has been reported in approximately 10%of patients (Liu et al. 2009). However, invasion of thebase of skull is a heterogeneous condition with arange of potential diagnostic settings. These includeminimal asymptomatic disease detected with highquality MRI, frank gross intracranial disease with apresentation spectrum ranging from a subtle bonyerosion of the skull base to extensive intracranialinvasion that may rarely include brain invasion.Subtle paralysis of cranial nerves, especially theabducens nerve, may accompany minimal diseasebut gross paralysis of multiple cranial nerves in NPCusually indicates significant direct erosion of theskull base, especially in patients with intracranialextension. Frequently, this may result from theFig. 24.5. Coronal contrast enhanced magnetic resonanceimage shows abnormal thickening and enhancement of theright cavernous sinus due to intracranial disease extension(dashed arrow). There is also perineural tumor trackingalong V3 across the widened right foramen ovale (curvedarrow). The solid arrow shows the normal appearing leftcavernous sinusinvolvement of the cavernous sinus directly by theprimary disease, but perineural disease extensionmay also occur, especially along the third division ofthe trigeminal nerve (Fig. 24.5). There is evidencethat minimal invasion of the skull base or minimalcranial nerve involvement is by no means as prognosticallydetrimental as very gross intracranialextension (Nishioka et al. 2000), further emphasizingthe rationale for why the AJCC has emphasizedthe importance of clinical evaluation of cranialnerves in staging assessments (Greene et al. 2002).NPC patients with cranial nerve palsy and intracranialextension are both still classified as T4 by thecurrent TNM, and there is no sufficient data availableyet to create a subclassification of T4 (e.g., T4a vsT4b) such as that introduced in the 6th edition TNMfor other head and neck cancers (Greene et al. 2002;Sobin and Wittekind 2002). Future explorations ofTNM will likely consider this issue, and investigatorsshould attempt to assemble larger and more robustdata sets to permit base of skull and intracranial diseaseto be better characterized. By this means, thisgenerally ominous but heterogeneous situation maybe classified more optimally in the future.