Case 1 -

Reactive Lymphoid Hyperplasia Paul E. Wakely, Jr.

Clinical History A 32 y/o woman presents with an enlarged 2.0 cm. slightly firm right cervical lymph node. The node has been present for about 6 weeks. She complains of no constitutional symptoms. Cytopathology Case 1 - Figure 1 - Case 1 - Figure 2 - Case 1 - Figure 3 - very cellular smears a polymorphous population of lymphocytes dispersed in a single cell pattern with accompanying LGBs. small "mature" lymphocytes are the dominant cell with a variable number of other transformed cells including immunoblasts, centrocytes, and plasmacytoid lymphocytes. tingible body macrophages(TBM) are uncommon in this case. Flow cytometry showed a polyclonal B- and T-cell population. Diagnosis: Reactive Lymphoid Hyperplasia Discussion As in tissue pathology, methodical assessment of the aspiration smear is critical to establishing a correct diagnosis. One must not simply examine individual cell morphology, but a total of five important components to the smear should be critically evaluated (Suen K. Diagn Cytopathol 1991; 7:335): Systematic Evaluation of Aspirate Smears Smear Cellularity. Cell arrangement/architecture. Cell Composition. Cell Morphology. Smear Background Two basic tenets used in recognizing cells as lymphoid on a smear [regardless of whether they are benign or malignant] are: a.) cell distribution predominantly as non-clustered, individual cells (single cell pattern), and b.) the presence of isolated globular or flake-like cytoplasmic fragments [lymphoglandular bodies, a.k.a lymphoid globules] in the smear background. Lymphoglandular bodies (LGBs): thought to derive from the fragility of lymphoid cell cytoplasm. Romanowsky stained smears: pale blue or blue-gray and may contain tiny vacuoles. Papanicolaou stained smears: difficult to see. Table 7. Lymphoglandular Bodies Lymphoid Tissue / Cells Small Cell Carcinoma Seminoma / Germinoma Granulocytic Sarcoma Rare: non-lymphoid pediatric small cell tumors in general the absence of LGBs should make one reconsider the cells on a smear as being lymphoid. lack of cell aggregation is a very good general rule for lymphoid cells, but is not an absolute since non-lymphoid cells can occasionally dissociate from each other, and conversely, some lymphoid smears have areas where cell aggregation is present. Smear thickness, spreading technique, and nature of the lesion all contribute to this clustering. Overall, however, lymphocytes smear as isolated (single) cells. The greatest difficulty in FNA and imprint cytopathology of lymph nodes is the distinction of reactive lymphoid hyperplasia (RLH) from a lymphoproliferative neoplasm. A major feature used in histopathology to clarify this problem[tissue architecture] is missing from smears, thereby exacerbating a challenging problem. Since classification by architectural pattern is not possible, the principal morphologic parameter used is cell size and smear composition as major discriminators. Immunophenotyping, a tool available to histopathologists, can and should be utilized by cytopathologists on every lymph node aspirate suspected of harboring a non-Hodgkin lymphoma. Note: RLH is characterized by having a true range (heterogeneous population) of lymphocytes and often non-lymphocytic cells present. Table 8. POLYMORPHOUS = REACTIVE HYPERPLASIA MONOMORPHOUS = MALIGNANT LYMPHOMA major exception: minimally reactive lymph node(see mantle cell lymphoma section) If one examines the components of the hyperplastic lymph node histologically one finds a variety of cells occupying different parts of the node (Table 8 ). Back and forth excursions of FNA randomly capture lymphocytic and non-lymphocytic cellular elements from different regions, commingle them within the barrel of the needle, and then expel them as an unordered mixture onto the slide. Nearly all aspirates of reactive lymphoid hyperplasia will have small mature lymphocytes as the most numerous cell type. Even those authors who subdivide reactive hyperplasia into various stages of reactivity (early, mid, and late phases) have demonstrated the predominance of small round mature lymphocytes with variations in the number of other lymphoid cells. Lesser numbers of follicular center cells - large noncleaved (centroblasts) and small/large cleaved (centrocytes), and immunoblasts are seen. Plasma cells and tingible body macrophages constitute <10% of cells in most reactive nodes. Non-neoplastic lymphadenopathy associated with increased plasma cells includes toxoplasmosis, syphilis, tuberculosis, rheumatoid arthritis, anticonvulsant therapy, and Castleman's disease(plasma cell variant). Table 9. LYMPH NODE MICROANATOMY Area Predominant Cell Cortex Small(B) lymphocyte   Follicular dendritic cells(FDC)   Follicular center cells - centroblasts and centrocytes   Tingible body macrophages(TBM) Paracortex Small(T) lymphocyte   Interdigitating reticulum cells/Langerhans' cells   Immunoblasts Medulla Plasmacytoid lymphocytes   Plasma cells   Immunoblasts Miscellaneous Capillaries, endothelial cells, mast cells, eosinophils Little stroma in reactive hyperplasia Þ moderately to highly cellular smears. Degree of cellularity has no direct correlation with the benign or malignant nature of lymphoid cells on a smear. An exception to the single cell architecture in reactive hyperplasia is the presence of follicular center (FC) fragments, and D&L [dendritic/lymphocytic] aggregates. FC fragments are microscopic bits of the germinal center captured by the fine needle and expelled intact as a loose syncytium of small lymphocytes, tingible-body macrophages(TBM), and FC cells held together by follicular dendritic cells(FDC). Table 10. Follicular Dendritic Cells round/oval hypochromic nucleus indistinct nucleolus occasional binucleation indistinct cell borders elongated branching cytoplasmic processes found only in B-cell dependent areas often obscured by lymphocytes in an FC fragment. Table 11. Follicular Dendritic Cell Proliferations Reactive follicular hyperplasia Castleman's disease Follicular Lymphoma Mantle Cell Lymphoma Nodular L-P Hodgkin Lymphoma Angioimmunoblastic T-Cell Lymphoma Follicular Dendritic Cell Sarcoma Short segments of capillaries sometimes exhibit branching in these FC fragments. Dendritic cells may commingle with lymphocytes to produce these D&L aggregates.Unlike FC fragments, D&L aggregates lack TBMs and capillary segments. Table 12. Tingible Body Macrophages [TBM], present in: reactive follicular hyperplasia high grade non-Hodgkin lymphoma Hodgkin's lymphoma lymph node metastases partial node replacement by any type of lesion rare - absent in nodal small cell types of malignant lymphoma Knowledge of the clinical characteristics of the node: size, duration, firmness are important parameters that are often missed if the clinician performs the aspiration. Just as essential is immunophenotyping which can often resolve this situation. Some of the elements that are regularly absent in smears of Reactive Hyperplasia include: markedly pleomorphic cells atypical mitoses individual cell necrosis an effluent of cellular debris If any of these features exist, smears should be re-evaluated to assure that another disease process is not present. A truly heterogeneous lymphocyte population on the smear helps to narrow the differential diagnosis to about four entities: reactive hyperplasia Hodgkin lymphoma (HL) partial node involvement marginal zone lymphoma peripheral T-cell lymphoma Immunophenotyping by flow cytometry is of little help if HL is suspected, but cytocentrifugation of the collected cells and immunophenotyping of these smears can greatly assist in this differential diagnosis. This is discussed in detail in case #3. The salient features of a reactive lymph node are: Table 13. Reactive Hyperplasia – Cytomorphology Moderate to high cellularity Single cell (dissociated) pattern predominates KEY: True lymphocyte cell heterogeneity, i.e. polymorphism Follicular center fragments common Tingible-body macrophages common Lymphoglandular bodies Table 14. Reactive Lymphoid Hyperplasia – Differential Diagnosis Small Cell Malignant Lymphomas Partial Node Involvement Hodgkin Lymphoma Non-Specific Benign Lymphadenopathy. e.g. PTGC, Castleman's, HIV associated lymphadenopathy Non-neoplastic lymphadenopathies that are difficult if not impossible to diagnose using FNA [criteria used in their recognition require knowledge of size and/or spatial relationships within the node]: Table 15. Benign Lymphadenopathies Not Specifically Diagnosable by FNA Progressive Transformation of Germinal Centers Castleman Disease Vascular transformation of lymph node sinuses Lymph Node Infarct Sinus Histiocytosis Toxoplasma lymphadenitis. HIV associated lymphadenopathy Most of these entities mimic the cytomorphology of reactive hyperplasia. Castleman's Disease (Angiofollicular Hyperplasia) Believable reports regarding the ability to specifically diagnose this lesion with any degree of confidence by FNA are severely limited, and somewhat doubtful. Our own experience is that the aspirate looks like reactive lymphoid tissue, and only the clinical picture combined with this appearance can at most suggest the diagnosis of Castleman disease. The involuted germinal centers and hyalinized vascular pattern (the most common variant) surrounded by concentric layers of small lymphocytes producing the so-called "onion skin" pattern of tissue sections is lost in smears. Some authors have described enlarged "dysplastic" FDCs as a possible clue to the diagnosis. In smears, the vascular proliferation of Castleman disease can look identical to the vascular branching seen in FC fragments of reactive hyperplasia. Too few cases of the plasma cell variant exist to comment on diagnostic reliability. References for All Cases