Beta Thallasemia / Thalassemia major, ''hair appearance'' is due to chronic haemolytic anamemias (due to hyperplasia of erythroid lineage in the bone marrow ). The cranial vaults space widens as there is a constant attempt to obtain more space for erythropoiesis within the bone marrow - the hyperplasia. The is also trabecular destrucion thickening of the remaining trabeculae - all of these features give the characteristic appearances.
Differentail includes - Thalassemia, Sickle Cell Anemia and Hereditary Spherocytosis (All can give the calssic "hair on end" x-ray pattern)
