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Introduction
In head and neck squamous cell carcinoma cases, the histopathological identification of lymph nodes containing tumour metastasis with extracapsular spread is a poor prognostic indicator; it has been associated with a 50 per cent decrease in survival and an approximately 1.5- to 3.5-fold increase in regional recurrence.1-3 In addition, large, multicentre studies have established histologically identified extracapsular spread as a major determinant of whether a patient would benefit from adjuvant chemotherapy.4 Therefore, the ability to predict lymph node extracapsular spread prior to treatment may be helpful in guiding subsequent therapy, both in non-surgical cases (which would benefit from concurrent chemoradiotherapy) and surgical cases (which may require adjuvant chemotherapy).
Contrast-enhanced computed tomography (CT) is the imaging modality most commonly used to evaluate cervical lymph node status. The CT criteria for lymph node analysis include: size, the presence of central necrosis, and the appearance of a cluster of lymph nodes in the expected drainage path of a tumour. However, such analysis may not be accurate in the setting of recent surgery, radiation or infection.5
The best radiological predictor of lymph node metastasis is a finding of central lymph node necrosis, which has been reported to carry nearly 100 per cent accuracy in predicting the presence of metastatic disease.6,7 Radiologically, lymph node central necrosis is defined as a central area of low attenuation surrounded by an irregular rim of enhancing tissue.5
Two entities may mimic malignant lymph node central necrosis: lipid metaplasia and abscess. Lipid metaplasia is fatty degeneration secondary to inflammation or irradiation, and is usually found at the periphery of the node, while an abscess can typically be differentiated clinically.
Radiological findings which suggest lymph node extracapsular spread comprise nodal capsular enhancement, infiltration of adjacent fat or muscle planes, and capsular contour irregularity.8,9 The use of CT for the identification of extracapsular spread has a sensitivity of 81 per cent and a specificity of 72 per cent, compared with 57-77 per cent and 57-72 per cent, respectively, for magnetic resonance imaging (MRI).10 For MRI scanning, pre-contrast T1- and T2-weighted images are more sensitive than gadolinium-enhanced T1-weighted images.9 Ultrasonography has been shown to be acceptably...