Neuroradiology

Sickle cell anaemia

an autosomal recessive condition in which an abnormal beta chain in HbS (valine substituted for glutamic acid) results in erythrocyte sickling at a reduced oxygen tension; the deformed and fragmented erythrocytes associated with an increase in blood viscosity leads to occlusion of small blood vessels and infarction.

Four types of anaemia are recognized: homozygous sickle cell disease, severe anaemia; sickle cell haemoglobin C disease, mild anaemia; sickle cell alpha thalassaemia, severe anaemia; sickle cell beta thalassaemia, mild to severe anaemia.

Clinical manifestations may involve different organs (liver, spleen) and systems (skeletal, respiratory, cardiovascular, urinary and nervous).

Nervous system involvement includes: cerebral infarction and stroke, present in 6 - 16% of affected children; intracranial haemorrhage; seizures; hemiplegia and coma; myelopathy and peripheral neuropathies; and neuropsychological deficits.

The underlying mechanism that leads to small vessel occlusion responsible for the ischaemic insults is thought to be endothelial injury from adhesions of sickled erythrocytes to endothelial cells. This results in internal elastic lamina fragmentation and degeneration of the muscularis, resulting in the large vessel vasculopathy observed in sickle cell patients.

CT, MR and angiography show the ischaemic and haemorrhagic tissue abnormalities and vessel anomalies. An unusual characteristic finding is extramedullary haemopoiesis shown by MR as extradural mass within the spinal canal with paramagnetic properties. Haemosiderosis of the pituitary (see haemochromatosis) may be seen in patients who have been repeatedly transfused.

 

GS