Hello doctor, Is there anyway that a CT scan can determine whether an enlarged lymph node is benign or malignant?
Hi. CT is a structural imaging method that relies on assessment of lymphnodes (LNs) based on their anatomy viz.size,shape, margins and enhancement patterns. Among these, size is still the most common criterion, a short axis diameter of more than 1 cm is generally accepted as a threshold for malignancy in most studies. However, the diagnostic sensitivity of this standard is weakened by the fact that many a times malignant LNs can be normal in size (false negative) and many infective nodes can be enlarged in size thus giving false positive results on imaging. Nowadays, CT is combined with PET (Positron emission tomography) to get both anatomical and functional information. It is called fusion imaging and is mainly used to diagnose and stage metastatic cancers such as lymphomas. CT also uses ionizing radiation (X-rays) that is another disadvantage which needs to be considered.  So to sum it all, structural imaging methods such as ultrasound, CT, conventional MRI do not distinguish benign LNs from malignant ones with 100 % accuracy. Conversely functional imaging methods such as DWI (diffusion weighted), PET have low spatial resolution and are time consuming. Therefore now we are seeing a shift towards fusion imaging techniques such as DWI-T2W1 MRI, PET/CT, etc., as these techniques bypass the above mentioned shortcomings.