Hair on end sign (mnemonic)

The hair on end sign refers to a radiographic appearance of the diploic space of the skull vault which results from a thickening of trabeculae as the diploic space expands. These trabeculae are perpendicular in orientation, interspersed by radiolucent marrow hyperplasia along with skull vault.

It is classically described with plain skull radiographs although can also be appreciated on CT or MRI . Causes include:

• thalassemia major
• sickle cell disease
• hereditary spherocytosis
• iron deficiency anemia

A useful mnemonic to remember the various causes of this sign is:

• HI NEST

Mnemonic

• H: hereditary spherocytosis
• I: iron deficiency anemia
• N: neuroblastoma
• E: enzyme deficiency, e.g. G-6-PD deficiency causing hemolytic anemia
• S: sickle cell disease
• T: thalassemia major