A-438 A. The current criteria for nodal involvement on CT/MRI

W. Schima | Sunday, March 10, 14:00 – 15:30 / Room E2

In a variety of diseases, such as metastatic disease, lymphoma and inflammation, lymph node enlargement can be seen. Thus, lymph node characterization is important to differentiate between benign and malignant disease. It is based on size (short axis diameter) and morphologic criteria, such as shape, homogeneity, and contrast enhancement. For abdominal nodes, location-specific size criteria apply (upper limit of normal: lower paraaortic 11 mm, upper paraaortic 9 mm, gastrohepatic ligament 8 mm, portocaval space 10 mm, retrocrural space 6 mm; pelvic nodes 10 mm). However, in clinical practice, often a universal size threshold of 10 mm is used in abdominal imaging. In chest CT, an upper limit of normal of 10 mm is universally applied. However, size criteria alone are unreliable: CT for lung cancer staging has a pooled sensitvity of 51 % (i.e., false negative diagnoses of metastatic deposits in normal-sized nodes), and a specificity of 86 % (i.e., false positive diagnoses due to enlarged reactive nodes). With MRI, the same size criteria apply. However, additionally features such as central necrosis (T2w fatsat or gadolinium-enhanced images) are suggestive of metastasis (or suppurative infection). Lymph node-specific USPIO MR agents can depict tumour deposits in subcentimeter pelvic nodes. Unfortunately, they did not reach market approval. DWI is helpful in identifying in lymph nodes as they exhibit high SI with higher b-values. However, diffusion pattern of benign and malignant nodes overlap, so that ADC values do not aid in characterization. Despite the use of modern MDCT and MRI techniques, lymph node characterization needs further improvement.

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