The asplenic state is a favourite topic of the examiners. Septic complications of asplenia featured in Question 9 from the first paper of 2013. Question 12 from the second paper of 2008 asked about pneumococcal meningitis in the post-splenectomy patient.
The functions of the spleen are briefly visited in this 2011 paper, and explored to great depth in this comprehensive review article from Nature.
You probably had it removed.
Reasons for this include:
Alternatively, it may be congenitally absent.
How much spleen do you need for normal phagocytic function? Well. Apparently, 80-90% of an enlarged spleen can be removed without any adverse immunological consequence; the remnants (or heterotopic bits of a fragmented spleen) can regrow in a disorganised fashion around the peritoneum in a process termed "splenosis". It seems only about 30ml of splenic tissue is required for reasonably normal function.
One can also have a normal-looking spleeen and be functionally asplenic. The linked article contains a nice table, listing various differentials:
In case you were wondering, thorium dioxide was at one stage used as a radiological contrast medium.
The asplenic man is prone to infections by encapsulated organsisms.
Again, the usual culprits include the following:
Unusual culprits also include:
Key features of this immunocompromised condition:
Empirical therapy consists of:
The vaccinations prevent severe infection by encapsulated organisms - because the encapsulated organisms are poorly opsonised by complement, and the spleen was the only organ which could remove them. Thus, one must protect this patient from these bugs. There has been a 2011 revision of the guidelines for such prophylaxis:
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