[Doppler ultrasonography of superficial lymph nodes]

Normal lymph nodes (l.n.) are elongated and hypoechoic, with central echogenic hilum on B-mode, while color-doppler (CD) shows central hilar vascularization. Chronic inflammatory l.n. are elongated, with echogenic hilum, hilar vascularization on CD and resistance index (RI) 0.60-0.70. Acute lymphadenitis shows intensive hilar flow with RI<0.60; abscess of l.n. is anechoic with through transmission. Tuberculous l.n. are inhomogenously hypoechoic and rounded, with deformed hilar vascularization on CD, occasionally with centripetal flow. They may mimick malignant l.n. on CD due to vessel dislocation by granulomatous masses. L.n. in stage of micrometastasis are of similar structure as reactive l.n., with preserved hilar vascularization; as the metastasis grows, focal cortical expansion and/or destruction of intranodal structure with dislocation and compression of blood vessels may occur; vascular resistance is consecutively increased; in advanced stage of metastatic growth l.n. becomes rounded, hilum is not visible, cortex is heterogenous, occasionally with hyperechoic keratin deposits, unsharp nodal margin is the sign of extranodal neoplastic spread; mainly peripheral vascularization, with fragmentation, deformation and dislocation of intranodal vessels are seen on CD, with increased RI>0.80; necrotic areas are anechoic and avascular on CD. Lymphomatous nodes have preserved internal structure, sharp margins, hypoechoic cortex, frequently with through transmission; large arborized hilum may be displaced; abundant hilar flow is seen on CD, with normal or slightly increased vascular resistance. Although the sensitivity of B-mode and Doppler features of l.n. is mostly limited (false negative rate is significant), high specificity of some of them establishes sonography as a valuable complementary method in differential diagnosis of lymphadenopathy: the presence of hilar vascularization with RI<0.40 accurately indicates acute lymphadenitis, while predominantly peripheral flow pattern and RI>0.80 are typical of metastatic l.n. High enddiastolic velocities (EDV>9 cm/s) are only rarely seen in metastases, while very low EDV<1 cm/s indicates metastatic lymphadenopathy. As sonography is very suitable imaging method for puncture guidance, B-mode and CD analysis of l.n. need to be combined with aspiration cytology whenever possible, as it may considerably improve the accuracy of non-invasive patient diagnostic work-up. Literature on sonography of l.n. was reviewed, and selection of most relevant articles was made.