Hair on end appearance is seen in

Ans. is 'a' i.e. Thalassemia Hair-on-end appearance {or Hair brush sign) of the skull is a characteristic feature of chronic hemolysis usually seen in patients with thalassanemia and sickle cell anaemia. It results from accentuated vertical trabeculae between the inner and outer tables of the skull because of excessive bone marrow hyperplasia.Explanation: The marrow hyperplasia widens the diploic space and thins the outer table. There is trabecular destruction with thickening of the residual trabeculae. The alternating opaque, thickened trabeculae and radiolucent marrow hyperplasia produce the hair-on-end appearance.Hair-on-end sign, is also seen in few other conditions like iron deficiency anemia, and spherocytosis.The skull changes are more consistently severe in patients with thalassemia major than in those with any other condition that produces marrow hyperplasia.Hair on end appearance may not be seen in occipital bone, as marrow content of occipital bone is minimal.