Normal lymph node, microscopic

This benign reactive lymph node has a well-defined connective tissue capsule (♦), and beneath that a subcapsular sinus (+) where afferent lymphatics drain lymph fluid from tissues peripheral to the node. The lymph may contain macrophages and dendritic cells, both forms of antigen-presenting cells, carrying antigens to the node. Beneath the subcapsular sinus is the paracortical zone (▲) with lymphoid follicles having pale germinal centers with a predominance of B lymphocytes. In the germinal centers (∗), immune responses to antigens are generated, assisted by a darker mantle zone of mainly T lymphocytes. Central to the follicles are sinusoids extending to the hilum of the node. The efferent lymphatics drain out the hilum (◼).

Normal lymph node, microscopic

At high magnification, a lymph node follicle with a germinal center (◼) contains larger lymphocytes undergoing cytokine activation. At the lower right is the subcapsular sinus (+). The center of the lymphoid follicle—the germinal center—is where CD4 helper lymphocytes and antigen-presenting cells (macrophages and follicular dendritic cells) interact with B lymphocytes, leading to an antibody-mediated adaptive immune response.

Normal lymph node, microscopic

The nature of the cell population and function of a lymph node are shown in the left panel with an immunohistochemical stain for CD20, a B-cell marker. Note the larger number of B cells staining with the red-brown reaction product within the germinal center (♦) of a lymph node follicle, with additional B cells scattered in the interfollicular zone. The node in the right panel has been stained for CD3, a T-cell marker. Note the larger number of T cells around (◼) the germinal center of a follicle, with additional T cells extending into the paracortex.

Normal white blood cells, microscopic

The normal types of leukocytes that are routinely observed on the peripheral blood smear are shown here, including a segmented neutrophil, band neutrophil, eosinophil, basophil, lymphocyte, and monocyte. The red blood cells appear normal, and there is a normal platelet present. A complete blood count includes a total white blood cell (WBC) count. The types of leukocytes may be enumerated by a machine that measures size and chemical characteristics. A manual WBC differential count is performed by observing the peripheral blood smear with Wright-Giemsa stain by light microscopy.

Leukocytosis, microscopic

Increased numbers of granulocytes, both segmented neutrophils and band neutrophils, are present in this peripheral blood smear. An elevated white blood cell (WBC) count with neutrophilia suggests acute inflammation and/or infection. A very high WBC count (>50,000/mm ³ ) that is not a leukemia is known as a “leukemoid reaction” and much more pronounced than just the “left shift” with bandemia and the occasional metamyelocyte with acute inflammation. There can be an accompanying increase in “acute-phase reactants” in plasma, such as C-reactive protein (CRP). Inflammatory cytokines, such as tumor necrosis factor (TNF) and interleukin-1 (IL-1), stimulate proliferation and differentiation of marrow granulocytic cells.

Leukocyte alkaline phosphatase test, microscopic

Distinguishing leukemoid reaction from chronic myelogenous leukemia (CML) may be done with the leukocyte alkaline phosphatase (LAP) stain. Seen here are normal neutrophils with red granular cytoplasmic staining for LAP. Abnormal myeloid cells of CML are not as differentiated as normal myeloid cells. Counting granulocytic cells staining with LAP yields a score. A high LAP score is seen with a leukemoid reaction, whereas a low LAP score suggests CML. A leukemoid reaction is typically a transient but exaggerated bone marrow response to inflammatory cytokines, such as interleukin-1 and tumor necrosis factor.

Pelger-Huët anomaly, microscopic

Neutrophils appear bilobed on this peripheral blood smear, indicative of Pelger-Huët anomaly, a dominantly inherited defect of terminal neutrophil differentiation from mutations in the lamin B receptor gene. This is the heterozygous form. In the homozygous form neutrophils display just a single round nucleus without lobation, and may be associated with abnormal neutrophil function. Be aware of this condition when the “band” count is reported as high but the white blood cell count is normal, or the patient shows no signs of infection or inflammation. True “band” neutrophils have a bridge of chromatin connecting the lobes. In the setting of myelodysplasia, bilobed neutrophils represent pseudo–Pelger-Huët cells.

Chronic granulomatous disease, microscopic

The nitroblue tetrazolium (NBT) slide test aids in screening for nicotinamide adenine dinucleotide phosphate (NADPH) oxidase defects. Patient neutrophils are exposed to a stimulus, incubated with NBT, and made into a smear on a slide. Neutrophils with dark cytoplasmic granules of reaction product are counted. Normally, more than 95% of the granulocytes are positive as shown in the left panel. In chronic granulomatous disease (CGD), there is an absent or reduced function of the respiratory burst, the intracellular process in neutrophils dependent upon NADPH oxidase, which produces oxygen free radicals used to kill phagocytized organisms. An abnormal NBT test in CGD in the right panel shows absent staining of a neutrophil.

Chédiak-Higashi syndrome, microscopic

A history of recurrent bacterial infections along with giant granules seen in peripheral blood leukocytes is characteristic for Chédiak-Higashi syndrome. This disorder results from a mutation in the lysosomal trafficking regulator ( LYST ) gene on chromosome 1q42 that encodes a protein involved in intracellular trafficking of proteins. Microtubules fail to form properly, and the neutrophils do not respond to chemotactic stimuli. Giant lysosomal granules fail to function. Soft-tissue abscesses with Staphylococcus aureus are common. Other cells affected by this disorder include platelets (bleeding), melanocytes (albinism), Schwann cells (neuropathy), natural killer cells, and cytotoxic T cells (aggressive lymphoproliferative disorder).

Lymphadenitis, microscopic

This is pronounced reactive change in a lymph node, with a large germinal center showing prominent macrophages (↑) with irregular cytoplasmic debris (so-called tingible body macrophages). Blood vessels (♦) are also more prominent. Multiple shapes and sizes of leukocytes are present, indicative of a polymorphous population of cells, or polyclonal immune response, typical for a benign process reacting to multiple antigens. Generally, a benign reactive process stimulates rapid lymph node enlargement and tenderness with palpation on physical examination, and they also quickly diminish in size after the inflammatory process has subsided.

Lymphadenitis, necrotizing, microscopic

The reactive change in this lymph node is primarily necrotizing (pink, amorphous regions), with a radiating stellate pattern seen in the left panel. Necrotic pale leukocytes in a central abscess are surrounded by still viable blue lymphocytes in the right panel. More advanced lesions may have granulomatous features. This necrotizing inflammatory process is caused by Bartonella henselae, a gram-negative rod. A cat scratch may introduce the organisms that induce a papule at the inoculation site, then regional lymphadenopathy within 1 to 2 weeks, followed by resolution in 2 to 4 months.

Granulomatous lymphadenitis, microscopic

Infectious agents such as Mycobacteria and dimorphic fungi (“Crypto, Histo, Blasto, Cocci”) may become disseminated from poor immune function and involve tissues of the mononuclear phagocyte system, such as lymph nodes. When there is no evidence for infection, then sarcoidosis should be considered, particularly when noncaseating granulomas are present, as shown here. Note the asteroid body (↑) in the Langhans giant cell, an uncommon but characteristic feature of sarcoid granulomas.

Lymphadenopathy, CT image

Note the prominent mesenteric lymph nodes (♦) in this patient with mesenteric lymphadenitis. Benign and malignant processes can lead to lymph node enlargement. Infections are a common cause for tender lymphadenopathy because lymph draining from the site of infection reaches regional lymph nodes. The lymph fluid carries antigens and antigen-presenting cells to the node. Antigens may also circulate out of the regional node and be carried around the body by the bloodstream, reaching other lymphoid tissues where clones of antigen-specific memory lymphocytes can react to those antigens. After the infection or inflammatory process has subsided, the stimulated nodes diminish in size.

Infectious mononucleosis, microscopic

Epstein-Barr virus (EBV) infection transmitted by close human contact, often through saliva, most often in adolescents and young adults, causes “mono” with fever, sore throat, generalized lymphadenopathy, splenomegaly, and absolute lymphocytosis. EBV infected B cells elicit a cell-mediated immune response with CD8+ cytotoxic T cells that proliferate in lymphoid tissues, then appear in the peripheral blood as “atypical lymphocytes” shown here with abundant pale blue cytoplasm. Initially IgM antibodies are formed, both “heterophile” antibodies detected by a screening monospot test, and next more specific antibodies against EBV capsid antigens.

Acute lymphoblastic leukemia, microscopic

These white blood cells are leukemic blasts—very immature leukocytes with large nuclei that contain multiple small pale round nucleoli. These abnormal lymphocytes are indicative of acute lymphoblastic leukemia (ALL) and have the B-cell markers CD10, CD19, and CD22 as well as transcription factor PAX5. About 85% of ALLs are precursor B-cell neoplasms. The cells of ALL originate in the marrow, but often circulate to produce leukocytosis. Patients with ALL usually have generalized lymphadenopathy along with splenomegaly and hepatomegaly. Bone pain is common. ALL is more common in children than adults. Many cases of ALL in children respond well to treatment, and many are curable.

Leukemia, microscopic

Neoplastic proliferation of leukocytes results in a highly cellular marrow. The marrow between the pink bone trabeculae seen here is nearly 100% cellular, and it consists of the leukemic cells of acute lymphoblastic leukemia that have virtually replaced or suppressed normal hematopoiesis. There is a near-absence of adipocytes. The bone spicules are unlikely to become affected by the leukemic process. With diminished normal hematopoiesis there can be peripheral blood cytopenias. This explains the usual leukemic complications of infection (diminished normal leukocytes), hemorrhage (fewer platelets), and anemia (decreased red blood cells) that often appear in the clinical course of leukemia.

Lymphoblastic lymphoma, microscopic

Lymphoblastic features may be present in the non-Hodgkin lymphoma that mimics the leukemia of the same name, and both may coexist as lymphoblastic leukemia/lymphoma. Multiple mutations underlie their development. Shown here are large primitive cells resembling either pre-B, pre-T cells (lymphoblasts). About 85% of these malignancies are B-cell and most present as leukemia. The rest are T-cell in origin, often with NOTCH1 mutations, and over half present as a thymic mediastinal mass in teenage boys. These neoplastic cells may have TdT, CD1a, CD2, CD5, and CD8 positivity. Acute lymphoblastic leukemia is the most common childhood malignancy.

Chronic lymphocytic leukemia, microscopic

These mature-appearing lymphocytes in the peripheral blood are markedly increased in number. This form of leukocytosis is indicative of chronic lymphocytic leukemia (CLL), a disease most often seen in older adults, with a male-to-female ratio of 2:1. The cells often have B-cell markers CD19, CD20, CD23, but also CD5 (a T-cell marker). Monoclonal immunoglobulin is displayed on cell surfaces, but there is unlikely to be a marked increase in circulating immunoglobulin. The peripheral leukocytosis is highly variable. CLL responds poorly to treatment, but it is indolent. In 15% to 30% of cases, there is eventual transformation to a more aggressive lymphoid proliferation.

Small lymphocytic lymphoma, microscopic

At low power, the normal architecture of this lymph node is obliterated and is replaced by an infiltrate of small (mature-appearing) neoplastic lymphocytes. The infiltrate extends through the capsule (→) of the node and into the surrounding adipose tissue at the top. This pattern of malignant lymphoma is diffuse, effacing normal nodal architecture, so no lymphoid follicles are identified. Small lymphocytic lymphoma (SLL) is the tissue phase of chronic lymphocytic leukemia (CLL), and molecular and biochemical characteristics of these SLL cells are identical to those of CLL. About 5% to 10% of SLL cases transform into a diffuse large B-cell lymphoma (Richter syndrome).

Small lymphocytic lymphoma, microscopic

These infiltrates within liver are composed of small round blue lymphocytes. The tissue involvement of chronic lymphocytic leukemia (CLL) is called small lymphocytic lymphoma (SLL). Liver, spleen, and lymph nodes may become enlarged, although organ function is often not markedly diminished because the progression of disease is slow because CLL/SLL often has an indolent course. Chromosomal translocations are rare in CLL/SLL, although the immunoglobulin genes of some CLL/SLL patients are somatically hypermutated, and there may be a small immunoglobulin “spike” in the serum. An autoimmune hemolytic anemia appears in about one sixth of cases.

Non-Hodgkin follicular lymphoma, gross

This cross-section through the mesentery reveals multiple enlarged lymph nodes that abut each other and are nearly confluent. In contrast to carcinoma metastases, lymph nodes involved by lymphoma tend to have little necrosis and only focal hemorrhage. They grossly maintain a solid, fleshy tan appearance on sectioning. Low-grade non-Hodgkin lymphoma (NHL) such as this tends to involve multiple lymph nodes at multiple sites, whereas high-grade NHLs tend to be more localized and may involve just a single lymph node, a single group of lymph nodes, or a solitary extranodal site.

Follicular lymphoma, CT image

This abdominal CT scan with contrast enhancement shows prominent periaortic lymphadenopathy (□) involving multiple nodes in a patient with low-grade non-Hodgkin follicular lymphoma. This appearance could represent any lymphoid neoplasm, however. Lymphadenopathy is the hallmark of many lymphoid neoplasms. Leukemia describes neoplasms with extensive bone marrow involvement and often peripheral leukocytosis. Lymphoma describes proliferations arising as discrete tissue masses either in lymph nodes or at extranodal sites. Hodgkin lymphoma (HL) is clinically and histologically distinct from the non-Hodgkin lymphomas (NHLs), is treated in a unique fashion, and is important to distinguish. All HLs and two thirds of NHLs manifest with nontender nodal enlargement. Plasma cell neoplasms composed of terminally differentiated B cells most commonly arise in the bone marrow, rarely involve lymph nodes, and rarely have a leukemic phase.

Follicular lymphoma, microscopic

The capsule of this lymph node has been invaded, and lymphoma cells extend into the surrounding adipose tissue (♦). The follicles are numerous, crowded, and irregularly shaped, giving a nodular appearance. This follicular form of B-cell lymphoma often has markers CD19, CD20, and CD10. In 90% of cases, a karyotype shows the t(14;18) translocation, which brings the IgH gene locus into juxtaposition with the BCL2 gene, leading to overexpression of the BCL2 protein, which inhibits apoptosis and promotes survival and accumulation of the abnormal lymphoid cells. One third to one half of cases may transform to diffuse large B-cell lymphoma.

Diffuse large B-cell lymphoma, microscopic

Many non-Hodgkin lymphomas (NHLs) in adults are large-cell lymphomas like the one shown here at medium power. Most are sporadic and of B-cell origin. The cells seen here are large, with large nuclei having prominent nucleoli, and moderate amounts of cytoplasm. Mitoses are frequent. The cells often mark with CD10, CD19, and CD20, but are negative for terminal deoxynucleotidyl transferase. The BCL2 gene may be activated. Dysregulation of BCL6, a DNA-binding zinc-finger transcriptional regulator required for the formation of normal germinal centers, is often present. Diffuse large B-cell lymphoma tends to be localized (low stage), but with more rapid nodal enlargement and a greater propensity to be extranodal than low-grade NHLs.

Diffuse large B-cell lymphoma, gross

Large-cell non-Hodgkin lymphomas have a propensity to involve extranodal locations like liver shown here. The Waldeyer ring of oropharyngeal lymphoid tissues, including tonsils and adenoids, is often involved, as can be liver, spleen, gastrointestinal tract, skin, bone, and brain. Marrow involvement occurs late in the course, and leukemia is rare. Seen here on cut surface of liver are two rounded pale tan mass lesions (→). The color can range from white to tan to red, often intermixed. Diffuse large B-cell lymphoma can be associated with immunosuppressed states, such as HIV/AIDS, whereas another subset arises with Kaposi sarcoma herpesvirus infection and leads to body cavity involvement marked by malignant pleural or peritoneal effusions. These aggressive neoplasms may respond to multiagent chemotherapy.

Burkitt lymphoma, microscopic

Seen here involving small intestinal mucosa are large infiltrating cells of Burkitt lymphoma (BL), one of the most common lymphomas in Africa, which most often appears in children and young adults and involves extranodal sites, particularly the mandible or the abdomen. In the United States, abdominal involvement is the most common presentation. The cells mark for CD10, CD19, and CD20, BCL6, and surface IgM. Mitoses as well as apoptosis with cellular debris cleared by large macrophages producing a “starry sky” pattern are prominent features. All forms of BL are associated with t(8;14) of the MYC gene on chromosome 8 to the IgH locus. Latent Epstein-Barr virus infection occurs in essentially all endemic tumors, about 25% of HIV-associated lesions, and 15% to 20% of sporadic cases.

Multiple myeloma, gross

This skull shows multiple round red “punched-out” lesions of multiple myeloma. The focal areas of plasma cell proliferation result in bone lysis to produce these multiple lytic lesions. Such lesions can produce bone pain. A solitary lesion is termed plasmacytoma. Myeloma results from a monoclonal proliferation of well-differentiated plasma cells often capable of producing light-chain and heavy-chain immunoglobulins. Proliferation and survival of these cells depends upon elaboration of IL-6 by plasma cells and marrow stromal cells. Cytogenetic abnormalities may include t(6;14) or t(11;14), which juxtaposes the IgH locus with the Cyclin D3 gene or Cyclin D1 gene, respectively.

Multiple myeloma, x-ray

The “punched-out” circular lytic lesions (+) in the skull seen here are the result of multiple myeloma in an older adult. These bone lesions consist of a neoplastic proliferation of plasma cells that can lead to hypercalcemia and an elevated serum alkaline phosphatase. A serum monoclonal globulin spike is typical. Increased production of immunoglobulin light chains can lead to excretion of the light chains in the urine, termed Bence Jones proteinuria. The diminished amount of normal circulating immunoglobulin increases the risk for infections, particularly with bacterial organisms, such as Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, and Escherichia coli.

Multiple myeloma, magnetic resonance imaging

The rounded lucency (▲) seen here in a vertebral body on a T2-weighted magnetic resonance image is one focus of plasma cell proliferation in a case of multiple myeloma. This patient had painful lytic lesions in multiple bone sites. The total serum immunoglobulin level is often increased, with an immunoglobulin “spike” (of “M protein”) seen on serum protein electrophoresis, and monoclonal bands of a single heavy-chain or light-chain class on immunoelectrophoresis of serum. Half of myelomas produce IgG, and a fourth produce IgA. In 60% to 70% of cases, increased light chains (either kappa or lambda), known as Bence Jones proteins, are produced and excreted in the urine, are toxic to renal tubules, and can lead to tubular injury with renal failure. The excessive light-chain production may lead to the amyloid light chain (AL) form of amyloidosis, with deposition of amyloid in many organs.

Plasmacytoma, CT image

The destructive, expansile lytic lesion (▲) involving the L2 vertebral pedicle on the left in this abdominal CT scan is a solitary plasmacytoma. Bones in the axial skeleton are most often involved with plasma cell neoplasms. The focal lesions typically begin in the medullary cavity, erode cancellous bone, and progressively destroy the bony cortex, leading to pathologic fractures, typically vertebral compressed fractures. The bone lesions appear radiographically as “punched-out” defects, usually 1 to 4 cm in diameter. About 3% to 5% of plasma cell neoplasms are solitary, but many progress to myeloma. Cytokines produced by the tumor cells include MIP1α that upregulates the receptor activator of nuclear factor kappa-B ligand (RANKL), which serves as an osteoclast-activating factor.

Multiple myeloma, microscopic

In this bone marrow biopsy section, as in most myeloma cases, there are sheets of plasma cells very similar to normal plasma cells, with eccentric nuclei and abundant pale purple cytoplasm. In fewer cases, the myeloma cells may be poorly differentiated. Usually, the plasma cells are differentiated enough to retain immunoglobulin production, but in less than 1% of cases, there is no increase in circulating immunoglobulin. Myelomas are typically detected by an immunoglobulin “spike” on protein electrophoresis or by the presence of Bence Jones proteins (light chains) in the urine. Immunoelectrophoresis characterizes the type of monoclonal immunoglobulin being produced.