Familial Nasopharyngeal Carcinoma 6

88 C. K. Ong and V. F. H. ChongabcFig. 8.9. Nasopharyngeal carcinoma with superior spreadthrough the foramen lacerum. (a) Axial contrast-enhancedfat-saturated T1-weighted MR image shows a left-sided nasopharyngealcarcinoma with predominantly posterolateralspread (arrow). (b) Coronal contrast-enhanced fat-saturatedT1-weighted MR image reveals further superior extensionthrough the left foramen lacerum (black arrow). Note theadjacent petrous internal carotid artery (white arrow). (c)High-resolution bone algorithm CT image shows no evidenceof skull base erosion8.3.2.5Superior SpreadAs noted earlier, foramen lacerum is within the confinesof the pharyngobasilar fascia and for a longtime, it was believed to provide an unimpeded routeof tumor infiltration into the intracranial cavity(Fig. 8.9). However, many studies have since showedthat more NPC spread intracranially via direct erosionof the skull base (Fig. 8.10) (Sham et al. 1991b).Skull base invasion is seen in up to one-third of thepatients, 12% on CT, and 31% on MRI (Chong et al.1996; Roh et al. 2004). MRI is able to detect earlymarrow signal changes secondary to osseous infiltrationwithout cortical bone erosion.8.3.3Staging: Tumor VolumePrimary tumor volume represents a significant independentprognostic factor in the treatment of malignanttumors, including NPC (Wei and Sham 2005).Larger tumors are related to increased number oftumor clonogens, as well as other adverse radiobiologicfactors including tumor hypoxia and thus theirrelative radioresistance (Johnson et al. 1995; Lartigauet al. 1993; Bentzen et al. 1991). There is an estimated1% increase in risk of local control failure with every1 cm 3 increase in primary tumor volume (Sze et al.2004). Such observations have prompted suggestionsto incorporate tumor volume into the TNM staging