Widening of the diploic space refers to expansion of the cancellous (spongy) bone between the inner and outer tables of the calvaria. The diploic space is the medullary cavity of the skull, and a location of normal physiologic hematopoiesis in adults. Thus, expansion of this structure most commonly occurs in the setting of chronically increased intramedullary hematopoiesis. The widened appearance is most commonly bilateral.
Most commonly caused by systemic pathologies such as:
- chronic hemolytic disorders: may be associated with vertical striations running in diploic space giving rise to the characteristic hair on end sign
- Paget disease (Tam o' Shanter sign)
- metabolic disorders
- 1. Lloret I, Server A, Taksdal I. Calvarial lesions: a radiological approach to diagnosis. (2009) Acta radiologica (Stockholm, Sweden : 1987). 50 (5): 531-42. doi:10.1080/02841850902795274 - Pubmed
- 2. Hollar MA. The hair-on-end sign. (2001) Radiology. 221 (2): 347-8. doi:10.1148/radiol.2212991231 - Pubmed