Nodal size is a not a good method of characterising lymph nodes. This is mainly because metastases can be present in non-enlarged lymph nodes and not all enlarged nodes are malignant.
Ultrasound has the accuracy of about 90% in differentiating malignant from benign nodes but are useless for imaging the lymph node groups in mediastinum, retroperitoneum, and deep pelvis. It is good for cervical nodes. Normal cervical nodes appear sonographically oval or flattened hypoechoic structures with varying amounts of hilar fat. The hilar are usually hypovascular. Malignant infiltration alters the US features of the lymph nodes, resulting in enlarged nodes that are usually rounded and show peripheral or mixed vascularity. They may have thickened outer wall, internal echoes, cystic formations, internal nodularity, and septations.
These are normal right axillary nodes of a 56 year old lady with suspected breast lump. The nodes are oval or oblong in shape with well-preserved hypovascular hilum. They measure about 1- 1.5cm in diameter. No breast lump was found on ultrasound.