Functions of the spleen
- Clearance of opsonized cells by splenic macrophages.
- Trapping of abnormal RBCs by the reticular meshwork.
- Antigen presentation – in the periarteriolar lymphatic sheaths and in the marginal zones of the lymphatic follicles (the T cell zones).
- Antibody production – in the mantle zone of the lymphatic follicle (the B cell zone).
- Haematopoiesis – in utero, during haemolysis, after stem-cell transplantation, etc.
- Reservoir function – especially of granulocytes and platelets in the red pulp.
- Haemostasis – production of factor VIII and von Willebrand factor by endothelial cells.
Causes of splenomegalyInfections
- Viral – EBV, CMV, etc.
- Bacterial – typhoid, brucellosis, bacterial endocarditis, etc.
- Fungal – e.g. histoplasma
- Protozoal – e.g. malaria, leishmania
- Chronic leukaemias – CML* and CLL*
- Acute leukaemias – AML and ALL
- Other myeloproliferative disorders – e.g. myelofibrosis*, polycythemia, etc.
- Other lymphoproliferative disorders – e.g. NHL, HD, hairy cell leukaemia*, etc.
- Miscellaneous – malignant histiocytosis, etc.
- Disorders of haemoglobin – sickling disorders and the thalassaemias*
- Disorders of the RBC membrane – hereditary spherocytosis*, hereditary elliptocytosis*, etc.
- Disorders of RBC enzymes – e.g. pyruvate kinase deficiency (rare)
Other non-malignant haematological diseases
- Autoimmune haemolytic anaemias*
- Thrombocytopenias – ITP*, TTP*
- Chronic neutropenias – e.g. Felty’s syndrome*
- Portal hypertension*
- Autoimmune diseases – e.g. SLE
- Chronic granulomatous conditions – e.g. sarcoidosis
- Storage diseases – e.g. Gaucher’s and Niemann-Pick’s
- Primary splenic problems – tumors, cysts, amyloid, etc.
- Metastatic tumors to the spleen (very rare)
* may be indications for splenectomy
Any thing that causes splenomegaly may be a cause of hypersplenism. Hypersplenism is defined as splenomegaly with any combination of clinically significant leukopenia, thrombocytopenia or anaemia.
Indications for splenectomy
- Massive splenomegaly causing severe local symptoms
- Splenic trauma
- Splenic tumors
- Staging of lymphoproliferative disorders such as Hodgkin’s disease
Hyposplenism – causes
- Haematolgical – sickling disorders, NHL and HD, Fanconi’s anaemia
- Immunological – SLE, rheumatoid arthritis, mixed connective tissue disease, Sjogren’s syndrome, chr. active hepatitis, ulcerative colitis, Crohn’s disease, graft versus host disease
- Anatomic – congenital asplenia or hyposplenia, splenic vein occlusion, irradiation, tumors, amyloidosis, etc.
Complications of splenectomy
- Post-splenectomy sepsis (splenectomy must be avoided in children less than 5 years and infection control measures need to be taken before and after splenectomy – see below)
- Post-operative atelectasis
- Splenic rupture and bleeding
- Sub-phrenic abscess
- Thrombocytosis – causing thromboembolism
- Slightly increased risk of ischaemic heart disease
Post-splenectomy changes in the blood
- Red cell changes – target cells, acanthocytes, erythroblasts, Howell-Jolly bodies, Heinz bodies, Pappenheimer bodies, slight reticulocytosis
- Platelet changes – thrombocytosis, which may be persistent but which usually does not exceed 1000 x 109 / litre
- White cell changes – initial neutrophilia, which then regresses. Lymphocytosis and monocytosis may persist.
- General – more frequent in younger patients but can also happen in adults; may occur years after splenectomy but most common in the first few months; usually abrupt onset, rapid course and cardiovascular collapse (due to adrenal haemorrhage – Waterhouse-Friderichsen syndrome) are features especially if due to N. meningitidis.
- Pathophysiology – lack of splenic macrophages to clear opsonized microorganisms; lack of type-specific antibodies
- Causative organisms – Bacteria such as Str. pneumoniae, H. influenza (types band f), N. meningitidis, Ps. aeruginosa, E. coli and other encapsulated organisms; Protozoa such as Plasmodium and Babesia.
- Prevention – Avoid splenectomy if possible or delay till patient is older than 5 years; immunize with polyvalent pneumococcal, meningococcal and conjugated Haemophilus vaccines – preferably 2 weeks or at least 72 hours before splenectomy; prophylactic antibiotics such as Penicillin V 250mg (or Erythromycin if Penicillin sensitive) b.d. for 1 year post-splenectomy or till the patient is 18 years old; patient education; medical alert or other warning signs to be carried by the patient on his person.
- Treatment – after a quick examination, take blood and other appropriate cultures and start on oral or iv antibiotics, e.g. a 3rd generation cephalosporin.