Haematopathology

Understanding of haematopathology is important in anatomical pathology, as haematologic malignancies are often in the (clinical) differential diagnosis and may mimic small blue round cell tumours or lobular breast carcinoma.

The lymph node is discussed below; however, details are covered in the lymph node article and lymph node pathology article.

Bone marrow

Main article: Bone marrow

Bone marrows are important for understanding haematopathology. They are dealt with in the bone article.

Normal lymph node

Main article: Lymph node

Main article: Lymph node pathology

Microscopic

The microscopic lymph node architecture in described the lymph node article, along with B cell maturation and lymph node cell types.

The cells of the lymph node:

• Germinal center:
  • Centrocytes - cleaved nucleus.
  • Centroblasts - large dark, mitotically active, medullary aspect of germinal center.
  • Tingible body macrophages.
  • Follicular dendritic cells.
• Paracortex:
  • T lymphocytes.
  • Interdigitating dendritic cells.
• Mantle zone:
  • Immunoblasts (Memory B cells) - small lymphocytes.
• Medulla:
  • B lymphocytes.
  • Plasma cells.

Haematologic neoplasia

Historically, haematologic neoplasias were split into leukemia (disease of the bone marrow & blood) and lymphoma (disease in discrete masses -- usually lymph nodes). In the modern day, this distinction has blurred.

Myelodysplastic syndrome

Main article: Myelodysplastic syndrome

At first approximation, these can be thought of as "pre-leukemia/lymphoma".

Leukemia

Main article: Leukemia

These predominantly have blood/bone marrow involvement.

Lymphoma

Main article: Lymphoma

These form masses. They typically arise from lymph nodes or aggregates of lymphocytes.

Plasma cell lesions

Main article: Plasma cell neoplasms

Myeloproliferative neoplasms

Main article: Myeloproliferative neoplasms

This subset of haematopathology includes, among others, polycythemia vera. Historically, these were not classified as neoplasias.

Specific diagnoses

Hemophagocytic syndrome

Main article: Hemophagocytic syndrome

General

• Rare.

Microscopic

Features:

• Macrophages eat RBCs, WBCs.

Heparin-induced thrombocytopenia

• Thrombocytopenia due to heparin.

Classification:

• Type 1 - in first two days of exposure - considered non-immune and considered not to be serious.
• Type 2 - in the first 4-10 days - considered serious.

Diagnosis (simplified):

• 50% decline in platelets - within 4-10 days of starting heparin.
• HIT assay - several exist.

Disseminated intravascular coagulation

• Commonly abbreviated DIC.

General

• Usually associated with sepsis or septic shock.

Clinical:

• Schistocytes (red blood cell fragmentation).

Gross

Features:

• Pleural petechial haemorrhages.

Microscopic

Features:

• Microvascular occlusion.

Notes:

• Microvascular occlusion is also seen in thrombotic microangiopathies.

Cytometry - population cell marker quantification

Main article: Cytometry

Two techniques

1. Flow cytometry.
2. Laser scanning cytometry (LSC).

Common markers

• CD3, CD4, CD8, CD5, CD7.
• CD19, CD20, FMC7.
• Kappa, lambda.

Normal

• T-cells to B-cells usually 1:1.
• In reactive nodes T-cells predominate.
• Normal thymic tissue has cells that are positive for both CD4 and CD8.
• Kappa (k) and lambda (l) are not expressed by the same cell.
• Rule-of-thumb for normal k:l range is: <6:1 and 1:<3.
  • Lambda dominance is less common.

GS guidelines - non-malignant is:

• CD19 ~= CD20.
• CD5 = CD3.
• CD2 > CD3 and CD5.
• CD4 + CD8 ~= CD3.
• CD7 = the smallest number of T-cell.

Abnormal

See cytometry.

Abnormal sign out

Lymph Node, Right Posterior Triangle of Neck, Excision:
- Lymphoid tissue with abnormal architecture, predominantly small cells.
- Case will be sent to hematopathology for opinion.

See also

• Stomach.
• Lymph nodes.