A 29-year-old woman had a cranial MRI as part of a headache study in April, 2014, which showed widening of the diploic space and displacement of the outer table of the skull, hypointense to grey matter on T1-weighted sequences (fi gure). She had a history of congenital dyserythropoietic anaemia type III and had needed frequent blood transfusions until the age of 9 years, when she had a splenectomy. Since then she had had annual haematological follow-up and her haemoglobin had remained stable around 90–100 g/L (normal 120–158 g/L). The MRI showed no other abnormalities and she was given a diagnosis of tension headache, which was fi nally controlled with analgesics and behavioural therapy. Congenital dyserythropoietic anaemias are a group of rare hereditary disorders characterised by ineff ective erythropoiesis. The changes in the skull seen in our patient are caused by increased medullary erythropoiesis and marrow hyperplasia in response to chronic anaemia. Occasionally the trabeculae extend perpendicularly between the inner and outer skull tables through the diploe in the expanded bone marrow space, producing a “hair-on-end” appearance on radiography (fi gure). Skull erythropoiesis in a patient with congenital dyserythropoietic anaemia