L y m p h o m a
Lymphoma is divided into two big categories: Non-Hodgkin Lymphoma and Hodgkin Disease. Before we get into lymphoma, though, let's take a look at normal lymph node architecture as well as a few benign lymph node disorders.
Normal Lymph Node Architecture
• Primary follicles (B cells; unstimulated)
• Secondary follicles (B cells; after antigen stimulation)
• Germinal center 
• Follicle center cells: heterogeneous! Small, irregularly-shaped
lymphocytes and larger, round lymphocytes with nucleoli.
• Macrophages with ingested debris ("tingible-body macrophages").
• Mantle zone (small, unstimulated lymphocytes)
• Interfollicular (paracortical) area (T cells)
Benign (Reactive) Lymph Node Disorders
Follicular hyperplasia
• Morphology: Numerous, irregularly-shaped, enlarged secondary follicles
containing benign follicle center cells (heterogeneous mixture of
lymphocytes) and tingible-body macrophages.
• Causes:
• Follicular hyperplasia is a B-cell response to an immune stimulus of
some kind.
• Most of the time, we can’t tell the precise cause!
• Sometimes, there are morphologic clues that point towards a specific
cause (such as rheumatoid arthritis or HIV).
• Easy to confuse with follicular lymphoma (see below).
Interfollicular hyperplasia
• Morphology:
• Areas between follicles are expanded
• Mixture of cells: T cells, macrophages, eosinophils.
• Sometimes, see "partial effacement": the interfollicular area is so
expanded that the overall architecture of the node is hard to see – but
there will always be at least a few remaining follicles.
• Causes:
• Interfollicular hyperplasia represents a T-cell response to an immune
stimulus of some kind.
• Common stimuli include Epstein-Barr virus (which causes infectious
mononucleosis); occasionally drugs (especially dilantin) or vaccines may
elicit this response.
Benign vs. Malignant
It's important to be able to tell apart a benign disease (like follicular hyperplasia) from a malignant one (like follicular lymphoma). Here is a brief summary of the differences (this will make more sense after you've studied the lymphomas!).
Benign (follicular hyperplasia)
• Architecture preserved
• Marked variability in follicle size, shape
• Germinal center:
• Heterogeneous lymphocytes
• Tingible-body macrophages
Lymphoma
Lymphoma is divided broadly into two kinds: Non-Hodgkin Lymphoma and Hodgkin Disease (or Hodgkin Lymphoma). These two kids of lymphoma are very different both clinically and under the microscope.
Clinically, Hodgkin Disease often arises in a single lymph node (or lymph node chain), spreads contiguously (from one lymph node to another in a predictable fashion), and has a good prognosis. Non-Hodgkin Lymphoma often presents with more than one involved lymph node, spreads non-contiguously (may jump from a lymph node in the neck to the bone marrow), and generally has a bad prognosis.
Morphologically, there are big differences too. Non-Hodgkin Lymphoma is classified into many, many subtypes, both B-cell and T-cell. Some subtypes are composed of small, regular-looking lymphoid cells, and other subtypes have big, ugly lymphoid cells. Hodgkin Disease is not classified as either a B-cell or a T-cell neoplasm, though it is clearly a lymphoid malignancy. It is characterized by the presence of Reed-Sternberg cells (which, incidentally, make up a very small percentage of the total tumor mass!).
