Familial Nasopharyngeal Carcinoma 6

Imaging in the Diagnosis and Staging of Carcinoma of Nasopharynx 89ait from being used routinely in daily practice. Themeasurement of tumor volume is tedious and involvesoperator-dependent tracing of the tumor outline.Several semi-automated systems of tumor volumemeasurement have been developed and are now availablefor NPC, reducing inter-operator as well as intraoperatorvariability (Clarke et al. 1995; Rasch et al.1997; Chong et al. 2004).8.3.4Staging: Nodal MetastasisbFig. 8.10. (a) Coronal contrast-enhanced fat-saturated T1-weighted MR image shows a large nasopharyngeal carcinomawith superior extension into the intracranial cavity(arrow). (b) Coronal bone-algorithm CT image reveals underlyingskull base erosion (arrow)system. In the current system, a small tumor involvinga critical area is often assigned a higher T-classificationwhen compared with a larger tumor confined within adefined anatomic site (Willner et al. 1999; Chen et al.2004; Chua et al. 1997). Early studies have indeedshowed a positive relationship between NPC tumorvolume and the TNM classification system (Chonget al. 2006).However, technical difficulty in standardizingaccurate tumor volume measurement has preventedCervical lymphadenopathy is very common inNPC, and is usually the initial presenting complaint(Fig. 8.11). Enlarged cervical nodes are evident in upto 75% of patients at presentation, 80% of who havebilateral lymphadenopathy (Chong and Ong 2008).Although retropharyngeal nodes are generally consideredas the first echelon nodes of NPC, they areonly seen in 65% of patients with nodal involvement(Chong et al. 1995). In the other 35% of patients, themetastases bypass the retropharyngeal nodes andspread directly to the internal jugular nodes.On imaging, the diagnosis of metastatic cervicallymphadenopathy in NPC (as well as other head andneck cancers) relies on the size and morphology ofthe lymph node. Generally, nodes along the jugularchain are considered malignant if their shortest axesare greater than 10 mm. A group of three or morelymph nodes that are borderline in size may also bedeemed malignant (Van Der Brekel et al. 1990). Inaddition, a lymph node is considered involved wherethere is imaging evidence of central necrosis or extracapsularextension (Van Der Brekel et al. 1990;Som et al. 1992).On MRI, the short axes of normal lateral retropharyngealnodes are usually less than 4.5 mm. Any lateralretropharyngeal node with short axis of 5 mm ormore should be regarded as malignant (Lam et al.1997; King et al. 2000). As medial retropharyngealnodes are usually not visible, any medial retropharyngealnodes detected on MRI are highly suspicious ofmetastatic involvement (Wang et al. 2009). Note thatretropharyngeal lymphadenopathy is not included inthe current TNM classification, as its prognostic significanceremains inconclusive and controversial (Maet al. 2007; Tang et al. 2008; Wang et al. 2009).Cervical nodal metastases in NPC, as a rule, showan orderly inferior spread and the affected nodes inthe upper neck are generally larger than those moreinferiorly. This reflects the route of spread of the