Definitive diagnosis is by lymph node biopsy (usually excisional biopsy with microscopic examination). Blood tests are also performed to assess function of major organs and to assess safety for chemotherapy. Positron emission tomography (PET) is used to detect small deposits that do not show on CT scanning. PET scans are also useful in functional imaging (by using a radiolabeled glucose to image tissues of high metabolism). In some cases, a gallium scan may be used instead of a PET scan. Types
There are two main types of Hodgkin lymphoma: classic Hodgkin lymphoma and nodular lymphocyte predominant Hodgkin lymphoma. The prevalence of classic Hodgkin lymphoma and nodular lymphocyte Hodgkin lymphoma are approximately 90% and 10%, respectively. The morphology, phenotype, molecular features, and, therefore, the clinical behaviour and presentation of the two types differ. Classic
Classic Hodgkin lymphoma (excluding nodular lymphocyte predominant Hodgkin lymphoma) can be subclassified into four pathologic subtypes based upon Reed–Sternberg cell morphology and the composition of the reactive cell infiltrate seen in the lymph node biopsy specimen (the cell composition around the Reed–Sternberg cell(s)). Presence of EBV in Reed-Sternberg cells is most commonly found in the subtypes lymphocyte depleted HL (>70%) and mixed cellularity HL (70%), whilst being less prevalent in lymphocyte-rich HL (40%) and relatively uncommon by comparison in nodular sclerosing HL. For the other forms, although the traditional B-cell markers (such as CD20) are not expressed on all cells, Reed–Sternberg cells are usually of B cell origin.
nodular sclerosis) a nodular aspect may appear.A fibrin ring granuloma may be seen. Microscopy

Microscopic examination of the lymph node biopsy reveals complete or partial effacement of the lymph node architecture by scattered large malignant cells known as Reed-Sternberg cells (RSC) (typical and variants) admixed within a reactive cell infiltrate composed of variable proportions of lymphocytes, histiocytes, eosinophils, and plasma cells. The Reed–Sternberg cells are identified as large often bi-nucleated cells with prominent nucleoli and an unusual CD45-, CD30+, CD15+/- immunophenotype. In approximately 50% of cases, the Reed–Sternberg cells are infected by the Epstein–Barr virus.Characteristics of classic Reed–Sternberg cells include large size (20–50 micrometres), abundant, amphophilic, finely granular/homogeneous cytoplasm; two mirror-image nuclei (owl eyes) each with an eosinophilic nucleolus and a thick nuclear membrane (chromatin is distributed close to the nuclear membrane). Almost all of these cells have an increased copy number of chromosome 9p/9p24.1.Variants:

Hodgkin cell (atypical mononuclear RSC) is a variant of RS cell, which has the same characteristics but is mononucleated. Lacunar RSC is large, with a single hyperlobulated nucleus, multiple, small nucleoli and eosinophilic cytoplasm which is retracted around the nucleus, creating an empty space ("lacunae"). Pleomorphic RSC has multiple irregular nuclei. "Popcorn" RSC (lympho-histiocytic variant) is a small cell, with a very lobulated nucleus, small nucleoli. "Mummy" RSC has a compact nucleus with no nucleolus and basophilic cytoplasm.Hodgkin lymphoma can be sub-classified by histological type.