Follicular lymphoid hyperplasia (FLH) is a common, benign enlargement of immune cells within lymph nodes or other lymphoid tissues. Despite its name, FLH is not cancer. It represents a reactive process, signifying a healthy immune response rather than an uncontrolled malignant growth. Understanding its nature can help alleviate concerns about enlarged lymph nodes.
Understanding Follicular Lymphoid Hyperplasia
Follicular lymphoid hyperplasia is characterized by an increase in the number and size of lymphoid follicles within lymph nodes. These follicles are specialized structures housing B cells, a type of white blood cell crucial for producing antibodies. In FLH, these normal immune cells proliferate in response to various stimuli, such as infections, chronic inflammation, or autoimmune conditions. This physiological response helps the body generate more lymphocytes to fight off threats. It is a self-limiting condition that resolves once the underlying cause subsides.
Distinguishing From Lymphoma
Distinguishing follicular lymphoid hyperplasia from follicular lymphoma, a type of non-Hodgkin lymphoma, is important for pathologists. While both conditions involve follicular structures within lymph nodes, their nature differs significantly. FLH is a reactive process involving normal, varied immune cells, whereas follicular lymphoma is a clonal proliferation of abnormal, malignant cells. Pathologists use several criteria to differentiate between them under a microscope.
A key distinction lies in the cellular architecture and composition. In FLH, follicles vary in size and shape, exhibit a “starry sky” appearance due to tingible body macrophages, and have sharply defined mantle zones. Follicular lymphoma, conversely, often shows uniform follicle size, a monomorphic cell population, and a less distinct or “fuzzy” mantle zone. The growth pattern in lymphoma may also involve follicles lying closely together throughout the lymph node.
Immunohistochemical staining plays an important role in diagnosis. Reactive follicular hyperplasia lacks BCL2 protein expression within its germinal centers, unlike follicular lymphoma, which often shows strong BCL2 expression in its neoplastic cells. FLH also displays polyclonality, meaning its B cells are diverse, while lymphoma is monoclonal, indicating a single abnormal cell origin. Markers like Ki-67, which indicates cell proliferation, can also assist; reactive germinal centers in FLH have a very high Ki-67 proliferation index, whereas most low-grade follicular lymphomas have a lower index.
How it is Diagnosed
Diagnosing follicular lymphoid hyperplasia and differentiating it from lymphoma requires a comprehensive approach, with a biopsy being the definitive diagnostic tool. Imaging studies, such as ultrasound or CT scans, can identify enlarged lymph nodes but cannot definitively distinguish FLH from lymphoma. These methods are supportive, helping to locate affected areas for further investigation.
A lymph node biopsy is important for accurate diagnosis. An excisional biopsy, which involves surgical removal of an entire lymph node, is often preferred as it allows pathologists to examine the full tissue architecture. This comprehensive view is important for distinguishing benign reactive changes from malignant processes. While core needle biopsies can also provide tissue, they may sometimes be insufficient for a definitive diagnosis of lymphoma subtypes due to sampling limitations.
Once the tissue is obtained, a pathologist examines it under a microscope. This examination involves assessing cellular morphology, cell arrangement, and the overall architecture of the lymph node. Immunohistochemistry, a laboratory technique that uses antibodies to detect specific proteins in cells, is routinely performed. This helps identify the presence or absence of markers like BCL2 and CD10, and assesses the Ki-67 proliferation index, which are important for distinguishing FLH from lymphoma.
Outlook and Management
The prognosis for follicular lymphoid hyperplasia is excellent, as it is a benign, reversible condition. In most cases, FLH does not require specific treatment, often resolving spontaneously once the underlying cause, such as an infection or inflammation, subsides. This “watch and wait” approach is a common management strategy.
Regular monitoring through follow-up appointments and occasional examinations is recommended to ensure resolution and detect changes. If enlarged lymph nodes persist or new symptoms develop, further investigation may be warranted. If FLH causes discomfort or aesthetic concern, surgical removal of the enlarged lymph node may be considered. Addressing the root cause, such as treating a chronic infection or managing an autoimmune disease, can also contribute to FLH resolution.