Lymph node diagnosis in oncologic imaging: a dilemma still waiting to be solved

The recognition of lymph node involvement is still one of the most challenging topics of diagnostic radiooncology. Above size, shape and contours, the intrinsic architecture of the node, its vessels and its metabolic activity are assessed and used for diagnostic conclusions. Conventional ultrasound has a high sensitivity for detecting enlarged lymph nodes, whereas its specificity is moderate. Tumor-associated alterations of intranodal angioarchitecture are not specific enough to allow reliable differential diagnosis of lymphadenopathy by color-coded Doppler ultrasound. Power Doppler ultrasound improved distinction between inflamed, reactive and metastatic nodes. Computed tomography (CT) is most widely used to detect and characterize lymph nodes in regions unaccessible to percutaneous ultrasound. However, diffuse lymph node enlargement secondary to infectious or granulomatous diseases cannot be discriminated from metastases or systemic lymphoma. Positron emission tomography (PET) provides superior staging information, as it offers functional information on tissue activity and has better sensitivity and specificity than CT for revealing neoplastic foci. Dual modality scanners (CT + PET) aid precise localization of diseased lymph nodes and give unique information regarding the activity of residual tumor tissue. Magnetic resonance (MR) imaging is comparable to CT in identifying lymph nodes. However, even quantitative assessment of signal intensity does not permit reliable follow-up of disease activity. MR lymphography opens a new chance to avoid understaging due to microscopic tumor invasion and overstaging due to peritumoural inflammation. With the expansion of this and other advanced techniques the need for invasive lymph node diagnosis will lessen.