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What is Hair on end appearance is seen in X–ray skull in –a)  Thalassemiab)  Hydrocephalusc)  Chronic malariad)  Sickle cell anemia and explain in detail?
Bone Changes in Thalassemia 

Bones become thin and pathological fracture may occur.
Massive expansion of the marrow of fade and skull produces characteristics .facies.
Severe maxillary hyperplasia and malocclusion.
Prominant widening of diploic spaces with "hair on end appearance" caused by vertical trabeculae.
Crew-cut appearance → striking expansion of hematopoietically active marrow that erodes existing cortical bone and induces new bone formation giving rise to crew cut appearance.

Causes of "Hair on end appearance" →Sickle cell anemia, hereditary spherocytosis, G-6-PD deficiency