Introduction
Background
Purpose
Rationale and discussion of the system
Overview and general considerations
Criterion “size”
Criterion “configuration”
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The category “texture” refers to the internal structure of a lymph node, which is defined as “homogeneous” (0 points), “heterogeneous” (1 point), “focal necrosis” (2 points), and “gross necrosis or any new necrosis” (3 points). Also, 3 points can be assigned if other features summarized under “entity-specific findings” are present: (i) cystic appearance (human papillomavirus positive squamous cell carcinoma of the neck, thyroid cancer, and non-seminomatous germ cell tumor), (ii) calcifications (thyroid cancer), and (iii) mucinous texture (mucinous adenocarcinoma) [12, 21, 22] (Figs. 2 and 3). “Texture” seems to be the most reliably assignable category, which is why the highest numerical values can be achieved here compared with the other categories.××
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The category “border” evaluates possible extranodal disease extension. This is very specific in the histopathological sense, but often difficult to diagnose with imaging methods [23]. Therefore, either 0 points (“smooth”) or 1 point (“irregular or ill-defined”) contribute to the configuration score in this category (Fig. 4).×
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The third category “shape” covers two features, the geometric shape and the delineation of the fatty hilum. Both features are usually well assessed on high-spatial resolution CT or MRI but are unspecific so that the maximum of 1 point can be assigned: 0 points (“any shape with preserved fatty hilum”) or (“kidney-bean-like or oval without fatty hilum”) 1 point (“spherical without fatty hilum”) (Fig. 5).×
Technical considerations
Structured reporting
Staging objectives
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To identify the presence and extent of regional nodal metastases to assign an N-staging category.
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To identify whether the extent of nodal disease will significantly alter the surgical approaches. For example, by increasing the extent of surgical exploration, or the requirement for the placement of vascular grafts.
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To determine whether the presence of metastatic nodal involvement designates M-stage disease.
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To identify the presence and extent of regional nodal enlargement with a view to planning biopsy.
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To distinguish between nodal enlargement due to malignancy and that due to benign hyperplasia.
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To acknowledge the limitation of imaging to detect microscopic disease in normal size nodes (currently possible to some extent only with MR lymphography and PET-CT).
Node reporting rules
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If there are multiple abnormal nodes in a specific nodal group, the node with the highest category should be reported with Node-RADS, unless the number of lymph node metastases influences TNM stage or treatment decision.
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In the context of TNM staging, Node-RADS 1 and 2 should be reported as N(−) and Node-RADS 4 and 5 as N(+). The decision how to report Node-RADS 3 should depend on the stage and histologic grade of the primary tumor (e.g., in Gleason 3 + 3 = 6 (UICC Grade 1) prostate cancer an obturator Node-RADS 3 lymph node should be reported as N(−), whereas, in adenocarcinoma of the pancreatic head, a peripancreatic Node-RADS 3 lymph node should be reported as N(+)). In the absence of histologic information, Node-RADS 3 should be reported as Nx.
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Although not required for TNM staging, it is sometimes necessary to classify in detail the sites of regional nodal involvement to facilitate surgical exploration (e.g., for head and neck tumors and in lung cancer—see relevant TNM/AJCC chapters for details) [1].
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There is often confusion about the precise anatomical location of nodal sites on cross-sectional imaging, particularly when planning radiotherapy or surgery. It is recommended that a standard nodal atlas is used depending on the use case.
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There is often confusion on nodal disease location at the border of regions. As a general rule, if a lymph node is located at the border of two regions, it should be assigned to the region in the direction of lymphatic drainage (e.g., common iliac as opposed to external iliac for prostate/bladder cancers).
TNM staging
RECIST reporting
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Since Node-RADS incorporates the configuration criterion, nodes with a short-axis diameter < 15 mm or < 10 mm can be assigned a Node-RADS score of 3, 4, or 5 while being considered malignant non-measurable lesions or normal nodes, respectively, according to RECIST 1.1. These must not be regarded as contradictory, rather they reflect the different purposes of the two systems (detection versus response assessments).
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Since RECIST 1.1 is purely size-based, nodes with a short-axis diameter < 15 mm can be assigned a Node-RADS score of 2 while being considered pathologic according to RECIST 1.1. Again, this must not be regarded as contradictory, rather they reflect the different purposes of the two systems (see above).
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In the scenario when RECIST 1.1 and Node-RADS differ, this should trigger a careful evaluation of the respective node on follow-up imaging.
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Immunotherapy can induce reactive nodal enlargement and configuration changes that probably alter the Node-RADS score; therefore, iRECIST should be used in the context of likely pseudoprogression, and Node-RADS is not applicable here.