Imaging features of primary extranodal lymphomas

Lymphomas are generally considered tumours of lymph nodes, but up to 40% arise extranodally. This group shows distinctive pathological, radiological, and clinical features. Different subtypes of extranodal lymphoma may show sufficiently specific radiological features to be of significant value in both establishing a diagnosis of lymphoma and ascertaining the exact subtype. Rapidly evolving lymphoma classifications and emergence of new entities have, however, hampered the accurate description of these features in the literature. In this review, we discuss the radiological appearances, using a variety of imaging methods, of the full spectrum of primary extranodal lymphomas, categorized according to the current World Health Organisation classification.