Disorders of the spleen and thymus

A) Spleen

Splenomegaly

The spleen is frequently secondarily involved in systemic disease and responds by enlarging.

Size-based differential (from the notes):

Massive (>1000 g)	Moderate (500–1000 g)	Mild (<500 g)
CML, PMF; Lymphomas; CLL/hairy cell; Malaria; Gaucher disease; Primary splenic tumor (rare)	Chronic congestive splenomegaly (portal HTN/splenic vein obstruction); Acute leukemias; Hereditary spherocytosis; Thalassemia major; AIHA; Amyloidosis; Chronic splenitis; TB, sarcoidosis, typhoid; Metastatic carcinoma/sarcoma	Acute splenitis (bacteremia); Acute splenic congestion; Infectious mononucleosis; Septicemia, SLE, intra-abdominal infections

Consequences of chronic splenomegaly

• Removal of excessive blood cells → anemia, leukopenia, or thrombocytopenia
• Platelets are especially prone to sequestration in red pulp
• Hypersplenism: increased removal of cellular blood components (distinct from mere enlargement)
• Risk of splenic rupture

Hypersplenism

Not synonymous with splenomegaly; it is the functional state of increased removal of blood components.

Causes:

• Widened splenic cords → premature destruction (portal hypertension, leukemia/lymphoma)
• Infections (Brucellosis, CMV, mononucleosis, malaria, toxoplasmosis, TB)
• Abnormal blood cells (e.g., hereditary spherocytosis)

Ruptured spleen

• Medical emergency: internal bleeding can be life-threatening
• Usually from blunt abdominal trauma, rarely from acute splenomegaly
• Small capsular tear at superior pole or hilum
• Symptoms: left upper abdominal pain/tenderness, dizziness, confusion

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B) Thymus

The thymus is central to T-cell differentiation and can be involved in T-cell lineage lymphomas.

Thymic hyperplasia

• Enlarged thymus due to increased cell number
• Often with lymphoid follicles / germinal centers in the medulla (reactive B-cells)
• Associated with autoimmune disorders: myasthenia gravis, SLE, RA
• Thymectomy may be beneficial in early disease

Thymoma

Tumor of thymic epithelial cells.

Classification:

• Benign/encapsulated thymoma — cytologically and biologically benign
• Malignant thymoma, Type I — cytologically benign, but locally invasive; rarely metastasizes
• Malignant thymoma, Type II (= thymic carcinoma) — cytologically malignant; metastasizes to lungs

Morphology:

• Macroscopy: lobulated, firm, grey-white masses; 20–25% invade surrounding tissue
• Microscopy: epithelial tumor cells + non-neoplastic thymocytes (immature T-cells)
  • Benign: medullary (spindle cells) or mixed
  • Malignant type II: squamous cell carcinoma-like appearance

Clinical:

• Rare, mostly middle-aged adults
• Local symptoms: cough, dyspnea, SVC syndrome
• Systemic: associated with myasthenia gravis (most important)
• Tumor removal often improves the neuromuscular disorder

💡 High-yield: Massive splenomegaly → MPNs (CML/PMF), lymphomas, malaria, Gaucher. Hypersplenism = increased removal of blood elements. Thymoma: epithelial origin; strongly associated with myasthenia gravis. Type I = locally invasive; Type II = thymic carcinoma.