Lymph nodes

Lymph nodes, abbreviated LNs, are very important in pathology. They are the site of metastases and/or may be the site of a primary tumour, i.e. lymphoma.

Haematopathology and lymphoma is dealt with in the haematopathology article. This article covers the basics of lymph nodes. Lymph node pathology is dealt with in the lymph node pathology article. Grossing is covered in lymph node grossing.

Clinical

Normal (clinical)

• Round.
• "Soft".
• Mobile.

Pathologic (clinical) - associations

• Rubbery = suggestive of lymphoma.
• Tender (hurts when ya touch it) = suggestive of infection.
• Fixed (immobile) = suggestive of cancer, usually carcinoma.
• Hard = suggestive of cancer.
• "Large" - cancer or infection.
  • What qualifies for "large" depends on the location in the body.

Radiologic

• Ellipical (as opposed to spherical) = may be cancer.
• "Large" = could be cancer or infection.
  • What qualifies for "large" depends on the location in the body.

Gross pathologic exam

Main article: Lymph node grossing

Normal:

• Firm (relative to adipose tissue).
• Glistening surface when cut.

Pathologic:

• White lesions, especially irregular = suggestive of carcinoma.
• White, glistening, with lobulated surface - "fish flesh" = suggestive of lymphoma.
  • Subtle lobulation (~1 mm) on section suggestive of follicular lymphoma.

Microscopic

Lymph node architecture

Lymph node architecture (superficial to deep):

• Capsule.
• Subcapsular sinus.
  • Place where metastatic cells often are found.
  • In a normal LN the vessels should be "open", i.e. have a discernible lumen.
• Cortex:
  • Follicles (superficial).
  • Paracortex (deep).
  • Cortical sinuses.
• Medulla:
  • Medullary cords.
  • Medullary sinuses.

Notes:

• Trabeculae - segment the LN radially, i.e. are spoke-like structures.

Lymph node follicles

Types of follicles:

1. Primary follicle - no germinal center (pale area).
2. Secondary follicle - have a germinal center (pale area) and mantle zone (rim of darker staining lymphocytes).

Germinal centre

Architecture:

• Paler at capsular aspect.
• Darker at medullary aspect.

Image:

• Secondary follicle (pathpedia.com).

Location and cell types

Germinal centers:

• Site of B lymphocyte proliferation; follicle center cells.
  • Centroblasts - usually superficial aspect. (??? deeper ???)
    • Darker, larger, nucleoli.
  • Centrocytes (mid germinal center).
    • Cells with cleavage.
  • Centrocytes (transforming to immunoblasts) - usually deeper aspect. (??? superficial ???)
    • Cells with cleavage.
• Tingible body macrophages - mid germinal center.
• Follicular dendritic cells.

Paracortex:

• Site of T lymphocytes.
• Interdigitating dendritic cell.

Medullary cords (site of immunoglobulin synthesis):

• B lymphocytes.
• Plasma cells.

Mantle zone:

• Memory B cells.
• Usually asymmetrical; thicker, i.e. more mantle cells, at capsular aspect.

Cell types

Follicular dendritic cells:

• Classically found in pairs.
• Large nucleus with:
  • Basketweave chromatin pattern.
  • Small central nucleolus.

Lymphocytes:

• See B lymphocytes section.

B lymphocytes

• B cells are best understood in the context of their maturation.

B cell cycle/maturation:

1. Centroblast (CB):
   • Appearance:
     • Large cells.
     • Round nucleus, dark.
     • Nucleolus (nucleoli).
     • Mitotically active.
   • Location:
     • Medullary aspect of germinal center.
2. Centrocytes (CC), AKA cleaved cells.
   • Appearance:
     • Cleaved nucleus
     • NOT mitotically active.
   • Location:
     • Mid germinal center.
3. Immunoblasts or memory B cells.
   • Appearance:
     • Small lymphocytes.
   • Location:
     • Peripheral blood, mantle zone.

Notes:

• Immunoblasts may be T cells or B cells; it is not possible to tell on morphologic grounds, i.e. without IHC.
• Memory device: centrocytes are light (it nearly rhymes).

Image:

• Lymphoid organs (healthsystem.virginia.edu).

Cell types - table

Cell	Location	Key feature	Other morphologic	IHC	Other	Image
Centroblast	germinal center	nucleolus	large cell, darker staining	CD10+, BCL6+ ???	other ?	image ?
Centrocyte	germinal center	cleavage	small cell, light staining	CD10+, BCL6+ ???	other ?	image ?
Follicular dendritic cell (FDC)	germinal center	mesh-like chromatin, usu. beside another one	large cell, unremarkable/small nucleolus	CD21+, CD23+	other ?	image ?
Tingible body macrophage	germinal center	abundant bubbly pale cytoplasm (with junk)	large cell	CD68+	other ?	image ?

Pathology

Main article: Lymph node pathology

LNs are very important in cancer staging and are, in many contexts, sampled routinely.

Sentinel lymph nodes

• Abbreviated SLN.
• LN sampling is associated with morbidity; thus, selective LN sampling is preferred.
• The most important LNs in a LN chain, in the context of cancer, are the ones that are adjacent to the tumour; these are known as sentinel lymph nodes.
• In lymph node positive disease, the most radioactive lymph node may be negative; this happens ~13% of the time in melanoma.

Use:

• Breast cancer - very common.
• Malignant melanoma - first context in which SLN sampling was done.

Lymph node metastasis

Main article: Lymph node metastasis

• Cancer that has spread to a lymph node.

See also

• Haematopathology.
• Lymph node pathology.
• Basics.

External links

• Lymph node architecture (umdnj.edu).