Page 1 of 12

PA19.4 | Splenomegaly — Causes & Differentiation — SDL Guide

Learning Objectives

Describe the normal structure and functions of the spleen (red pulp vs. white pulp).
Define splenomegaly and massive splenomegaly with clinical thresholds.
Enumerate the causes of splenomegaly using a mechanistic framework.
Identify the causes of massive splenomegaly and apply them in clinical reasoning.
Define hypersplenism and distinguish it from simple splenomegaly.
Explain the haematological effects of splenectomy and the associated infection risk.

INSTRUCTIONS

Splenomegaly is one of the most examined signs in internal medicine and surgical pathology. Mastering a mechanistic framework — not a raw memorised list — is the fastest route to answering both MCQ stems and long-case viva questions. This module builds that framework from first principles: spleen structure → functions → how each function, when overwhelmed or disrupted, produces the disease categories you see in the wards. Year-2 connects here to everything you have studied in Cluster H5 (haemolytic anaemias), H7 (CML), and H8 (lymphomas) — this is the integrating lens.

References

Robbins & Kumar: Pathologic Basis of Disease, 10th ed., Ch 13 (White Blood Cells, Lymph Nodes, Spleen, and Thymus) (textbook)
Harsh Mohan: Textbook of Pathology, 7th ed., Ch 30 (Diseases of the Spleen) (textbook)

Version 2.0 | NMC CBUC 2024

CLINICAL SCENARIO

A 34-year-old man from Bihar presents with a massively enlarged spleen reaching the right iliac fossa, mild fever for six months, and profound anaemia. His blood film shows no malaria parasites. His colleague — also from Bihar — had an identical presentation two years ago and responded to sodium stibogluconate.

Massive splenomegaly demands a short, specific differential. By the end of this session you will not only name that list but explain why each disease produces a spleen big enough to fill half the abdomen.

WHY THIS MATTERS

PA19.4 is tested in every university written paper as a structured long-answer question: "Classify the causes of splenomegaly with examples." It also anchors the clinical chapters on portal hypertension, haematological malignancies, and tropical infections. Surgeons and physicians both ask about hypersplenism and splenectomy consequences in post-graduate entrance examinations. There is no shortcut — the mechanistic framework is the shortcut.

RECALL

Before proceeding, activate what you already know:

Cluster H5 — thalassaemia major and hereditary spherocytosis both cause haemolytic anaemia. Where does the excess haemolysis occur?
Cluster H7 — CML is the prototypic myeloproliferative neoplasm. What is the key chromosomal abnormality?
Cluster H8 — lymphomas infiltrate lymphoid tissue. Can they infiltrate the spleen?
From Year-1 Anatomy: the spleen lies in the left hypochondrium, between ribs 9–11. A spleen you can palpate has at least doubled in size.

Hold these in mind — they will slot into the framework as you build it.

Normal Spleen: Structure and Functions

Three-panel medical diagram of the normal spleen showing gross compartments, red pulp filtration and pitting, and white pulp immune surveillance. — **Panel A:** Gross anterior spleen with capsule, hilum, red pulp ~75%, white pulp ~25%, central arterioles, and adult weight 150-200 g.. **Panel B:** Red pulp sinusoids, littoral cells, cords of Billroth, macrophages, 3-micrometer slit pores, normal flexible RBCs, aged rigid RBCs, Howell-Jolly bodies, Heinz bodies, parasites, filtration/culling, pitting, RBC reservoir, and platelet reservoir.. **Panel C:** White pulp with central arteriole, PALS T-cell zone, B-cell follicle, germinal centre, marginal zone, plasma cells, IgM production, opsonisation, immune surveillance against encapsulated bacteria, fetal haematopoiesis timeline, and adult extramedullary haematopoiesis in marrow failure such as myelofibrosis..

The adult spleen weighs 150–200 g. Its parenchyma has two compartments:

Red pulp (~75%) — sinuses lined by littoral cells (specialised macrophages) and cords of Billroth. Functions:
• Filtration/culling: removes aged, rigid, or abnormal RBCs that cannot deform through 3-µm slit pores between sinusoids and cords.
• Pitting: excises intra-erythrocytic inclusions (Howell-Jolly bodies, Heinz bodies, parasites) while returning the cell to circulation.
• Blood reservoir: stores ~30–40 mL RBCs and a platelet reservoir (~1/3 of total platelets).

White pulp (~25%) — lymphoid tissue arranged around the periarteriolar lymphoid sheath (PALS) of T cells, with follicles (B cells) forming germinal centres on stimulation.
• Immune surveillance: IgM production (especially against encapsulated bacteria); opsonisation.

Haematopoietic function: primary haematopoietic organ in the fetus (from week 5 to ~7 months gestation). In adults, extramedullary haematopoiesis resumes in the spleen only when marrow is replaced or severely damaged (e.g., myelofibrosis).

Medical illustration showing normal spleen histology at 40× magnification with labeled compartments, organizational diagram, and splenomegaly classification table. — **Panel A:** Red pulp sinusoids, littoral cells, cords of Billroth, white pulp, PALS (periarteriolar lymphoid sheath), primary follicle, central arteriole. **Panel B:** Schematic organization of red pulp and white pulp compartments with color coding. **Panel C:** Splenomegaly classification table showing weight ranges, clinical definitions, and associated causes for mild, moderate, and massive enlargement.

Splenomegaly and Massive Splenomegaly — Definitions

Four-panel medical diagram defining splenomegaly and massive splenomegaly by palpability, spleen weight, anatomical extent, diagnostic size categories, and major mechanisms. — **Panel A:** Anterior torso with left costal margin, normal spleen region, palpable splenomegaly, umbilicus threshold for massive splenomegaly, and right iliac fossa extension indicating approximately 3–5 kg spleen.. **Panel B:** Definition thresholds: clinical splenomegaly as palpable spleen usually greater than 400 g or below left costal margin, pathological splenomegaly as spleen weight greater than 250 g, and massive splenomegaly as beyond umbilicus or greater than 1 kg.. **Panel C:** Diagnostic size spectrum showing mild 250–500 g, moderate 500–1,000 g, and massive greater than 1,000 g splenomegaly with representative causes.. **Panel D:** Mechanistic framework of five causes: congestive, infective/inflammatory, haematological, infiltrative/storage, and neoplastic enlargement..

Splenomegaly is defined clinically as a palpable spleen (implying weight >400 g or extension below the left costal margin) and pathologically as spleen weight >250 g.

Massive splenomegaly — no universally agreed threshold, but conventionally: spleen extending to or beyond the umbilicus, or weight >1 kg. In practice, a spleen reaching the right iliac fossa weighs 3–5 kg.

Why size matters diagnostically: the degree of enlargement correlates loosely with the mechanism:

Degree	Examples
Mild (250–500 g)	Acute infections, congestive heart failure, early portal hypertension
Moderate (500–1,000 g)	Lymphomas, chronic hepatic disease, haemolytic anaemia
Massive (>1,000 g)	CML, myelofibrosis, kala-azar, malaria, Gaucher, thalassaemia major

Mechanistic Framework: Five Causes of Splenomegaly

A radial medical diagram shows an enlarged spleen at the center with five surrounding mechanisms of splenomegaly: congestive, infective/inflammatory, haematological, infiltrative/storage, and immune. — **Panel A:** Central enlarged spleen showing red pulp, white pulp, splenic artery, splenic vein, portal venous drainage, and the idea of exaggerated normal splenic functions.. **Panel B:** Congestive splenomegaly showing raised splenic venous pressure, passive congestion, sinusoidal dilatation, portal hypertension, and right-sided heart failure.. **Panel C:** Infective / inflammatory splenomegaly showing antigenic stimulation, white pulp hyperplasia, macrophage activation, red pulp expansion, malaria, mononucleosis, rheumatoid arthritis, and sarcoidosis.. **Panel D:** Haematological splenomegaly showing haemolytic stress, increased RBC filtration, work hypertrophy, leukaemia, lymphoma, and malignant haematopoietic infiltration.. **Panel E:** Infiltrative / storage splenomegaly showing distended macrophages containing stored metabolic substrate or protein deposits, Gaucher disease, and amyloidosis.. **Panel F:** Immune splenomegaly showing autoimmune activation, complement-tagged blood cells, phagocytosis, and macrophage hyperplasia..

Think of every cause of splenomegaly as an exaggeration of one of the spleen's normal functions. Five mechanisms cover the syllabus:

Congestive — raised splenic venous pressure → passive congestion → sinusoidal dilatation.
Infective/Inflammatory — antigenic stimulation → white pulp hyperplasia; macrophage activation → red pulp expansion.
Haematological — haemolytic stress (work hypertrophy of filtration) OR infiltration by malignant haematopoietic cells.
Infiltrative/Storage — accumulation of metabolic substrates or protein deposits distends macrophages.
Immune — autoimmune activation (complement-tagged cells) → macrophage hyperplasia.

Radial diagram showing anatomical spleen at center with five mechanistic categories of splenomegaly branching outward, each containing representative diseases — **Panel A:** Central spleen anatomy with five radiating categories: Congestive (portal hypertension, heart failure), Infiltrative (amyloidosis, Gaucher disease), Hematological (leukemias, lymphomas), Infectious (malaria, mononucleosis), and Inflammatory (rheumatoid arthritis, sarcoidosis) mechanisms.