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PA19.1-6 | Hodgkin Lymphoma — Gross & Microscopic Identification — Part 2

RS Cell Variants — Know All Four

A 2×2 histology-style comparison diagram shows the four Reed-Sternberg cell variants: mononuclear Hodgkin cell, lacunar cell, popcorn L&H cell, and mummified RS cell. — **Panel A:** Mononuclear Hodgkin cell showing single large nucleus, prominent eosinophilic nucleolus, pale cytoplasm, and mixed inflammatory background.. **Panel B:** Lacunar cell showing clear formalin-retraction lacuna, lobulated butterfly-like nucleus, smaller nucleoli, and pale fibrous bands of nodular sclerosis HL.. **Panel C:** Popcorn / L&H cell showing multilobated popcorn-like nucleus, small multiple nucleoli, lymphocyte-rich nodular background, and CD20+ / CD15− / CD30− immunophenotype.. **Panel D:** Mummified RS cell showing pyknotic shrunken nucleus, dense eosinophilic homogeneous cytoplasm, and necrotic or treatment-related background debris..

The classic binucleate RS cell has four variants. Each is associated with a specific subtype or context:

1. Mononuclear Hodgkin cell (H cell)
A mononuclear RS variant — single nucleus with the same large eosinophilic nucleolus. Common in all cHL subtypes. Individually non-diagnostic (requires classic RS or lacunar cells), but contributes to the overall picture.

2. Lacunar cell (nodular sclerosis)
The predominant neoplastic cell in nodular sclerosis. On formalin-fixed tissue, cytoplasm retracts, leaving the cell sitting in an apparent clear space (lacuna). The nucleus is lobulated (multi-lobed or 'butterfly'), nucleoli are smaller and less prominent than classic RS. This artefact of formalin fixation is subtype-defining.

3. Popcorn cell / lymphocytic and histiocytic (L&H) cell (NLPHL)
Found in Nodular Lymphocyte-Predominant HL. Large cell with a highly lobulated, multi-folded nucleus resembling popped corn. Nucleoli are small and multiple (inconspicuous compared to classic RS). Immunophenotype: CD20+, CD15−, CD30− — the opposite of cHL. Background is nodular with abundant small lymphocytes (not a mixed inflammatory infiltrate).

4. Mummified RS cell
A degenerate RS cell with pyknotic shrunken nucleus and deeply eosinophilic homogeneous cytoplasm. Seen in lymphocyte-depleted HL and in areas of treatment-related necrosis.

Medical illustration showing lacunar Reed-Sternberg cell variant in nodular sclerosis Hodgkin lymphoma with characteristic retraction artifact. — **Panel A:** Lacunar cell with lobulated nucleus, clear lacuna (retraction artifact), surrounding lymphocytes and connective tissue. **Panel B:** Schematic showing cytoplasmic retraction during formalin fixation creating the characteristic lacunar appearance.

Practical tip: In the examination slide, if you see cells sitting in clear spaces with lobulated nuclei and broad collagen septa — you are looking at nodular sclerosis with lacunar cells, not classic RS cells. Both count.

SELF-CHECK

A slide shows broad collagen septa dividing a lymph node into cellular nodules. Within the nodules, neoplastic cells have lobulated nuclei sitting in clear retraction spaces. Nucleoli are present but less prominent than in a classic RS cell. Which variant is this, and which subtype does it define?

A. Lacunar cell — nodular sclerosis Hodgkin lymphoma

B. Popcorn cell — nodular lymphocyte-predominant HL

C. Classic RS cell — mixed cellularity HL

D. Mummified RS cell — lymphocyte-depleted HL

Reveal Answer

Answer: A. Lacunar cell — nodular sclerosis Hodgkin lymphoma

Lacunar cells are the characteristic neoplastic element of nodular sclerosis. The 'lacuna' is a formalin-fixation artefact where cytoplasm retracts. Their presence alongside broad collagen septa is diagnostic of nodular sclerosis, the most common HL subtype. Popcorn cells define NLPHL; classic RS cells are universal but predominate in mixed cellularity; mummified cells appear in lymphocyte-depleted HL.

The Polymorphous Reactive Background

Diagram showing Hodgkin lymphoma as a small population of Reed-Sternberg cells within a large polymorphous reactive inflammatory background, with subtype-specific histologic patterns. — **Panel A:** Reed-Sternberg cells, RS-cell variants, small mature lymphocytes, eosinophils, plasma cells, histiocytes/macrophages, neutrophils, fibrosis/collagen, cytokine arrows, 1-5% malignant cells, 95-99% reactive background. **Panel B:** Nodular sclerosis pattern with lacunar cells, broad collagen bands, mixed inflammatory background, relatively fewer eosinophils. **Panel C:** Mixed cellularity pattern with classic Reed-Sternberg cells, eosinophils, plasma cells, histiocytes, and small lymphocytes. **Panel D:** Lymphocyte-rich pattern with sparse Reed-Sternberg cells, predominantly small mature lymphocytes, few eosinophils. **Panel E:** Lymphocyte-depleted pattern with numerous Reed-Sternberg cells, depleted lymphocytes, sheet-like tumour areas, and variable neutrophils.

HL is unique: the malignant cells (RS cells + variants) constitute only 1–5% of the tumour mass. The remaining 95–99% is a reactive inflammatory infiltrate driven by cytokines secreted by the RS cells.

Components of the background (learn to name each):
• Small mature lymphocytes — the dominant background cell in most subtypes
• Eosinophils — prominent in mixed cellularity; their presence alongside RS cells is a diagnostic clue
• Plasma cells — polyclonal, reactive
• Histiocytes / macrophages — scattered, may be prominent
• Neutrophils — variable, more in lymphocyte-depleted
• Fibrosis / collagen — thin strands in mixed cellularity; broad dense bands in nodular sclerosis

Subtype background comparison:

Subtype	Background signature
Nodular sclerosis	Lacunar cells + broad collagen bands + mixed but less eosinophil-rich
Mixed cellularity	Classic RS cells + eosinophils + plasma cells + histiocytes
Lymphocyte-rich	RS cells sparse; background almost entirely lymphocytes, few eosinophils
Lymphocyte-depleted	RS cells numerous; background depleted of lymphocytes, sheet-like
NLPHL	Popcorn cells in nodular background of small B-lymphocytes

The reactive background is not a bystander — it is the product of RS cell cytokine signalling (IL-5 → eosinophils; IL-13 → fibrosis; TGF-β → collagen deposition in NS).

SELF-CHECK

In a lymph node biopsy with classic RS cells, you observe a background rich in eosinophils, plasma cells, and histiocytes, without broad collagen bands. The RS cells are numerous and classic in appearance. Which subtype is most likely?

A. Mixed cellularity Hodgkin lymphoma

B. Nodular sclerosis Hodgkin lymphoma

C. Lymphocyte-rich Hodgkin lymphoma

D. Nodular lymphocyte-predominant HL

Reveal Answer

Answer: A. Mixed cellularity Hodgkin lymphoma

Mixed cellularity HL is characterised by classic RS cells in a background of eosinophils, plasma cells, histiocytes, and lymphocytes without the collagen bands of nodular sclerosis. It is the second most common subtype and strongly EBV-associated. Nodular sclerosis would show broad collagen bands and lacunar cells. Lymphocyte-rich has a background of predominantly lymphocytes with rare RS cells. NLPHL would show popcorn cells in a nodular B-cell background.

Nodular Sclerosis — Detailed Histology

Medical diagram showing nodular sclerosis Hodgkin lymphoma with collagen-banded nodules, lacunar cells, NS1 versus NS2 grading, and anterior mediastinal involvement in a young woman. — **Panel A:** Broad birefringent collagen bands, cellular nodules, partial effacement of lymph node architecture, thickened fibrotic capsule, polarised light inset. **Panel B:** Lacunar cell, clear pericellular lacuna, multilobed nucleus, prominent nucleolus, pale cytoplasm, formalin fixation artefact, occasional classic Reed-Sternberg cell. **Panel C:** NS1: abundant lymphocytes, scattered lacunar cells, few Reed-Sternberg cells; NS2: syncytial nests or sheets of lacunar cells, depleted lymphocytic background. **Panel D:** Young woman, anterior mediastinal lymph node mass, nodular sclerosis Hodgkin lymphoma clinical association.

Nodular sclerosis (NS) is the most common HL subtype (60–80% in developed countries) and the one most likely to appear in a Year-2 practical exam.

Diagnostic criteria (all three needed):
1. Partial or complete effacement of nodal architecture by broad, birefringent collagen bands that divide the node into cellular nodules (visible on both H&E and polarised light).
2. Presence of lacunar cells within the nodules (classic RS cells may also be present but are less dominant).
3. Characteristic thickened capsule — the capsule itself is fibrotic, not just the intraparenchymal bands.

WHO grades NS1 and NS2:
• NS1 (grade 1): classic lacunar cells, abundant lymphocytes, few RS cells — better prognosis
• NS2 (grade 2): syncytial variant — sheets of lacunar cells forming 'nests,' depleted lymphocytic background — higher grade behaviour

Why does formalin matter here? Fresh tissue or frozen sections do NOT show lacunae. The retraction artefact only appears after formalin fixation. In an exam, if asked 'why do lacunar cells only appear on formalin-fixed paraffin sections?' — this is your answer.

Clinicopathological note: NS preferentially involves mediastinal lymph nodes in young women. A anterior mediastinal mass in a 20-year-old female = NS HL until proven otherwise.