Widened Diploic Space

Diffuse thickening of the calvarium can be caused by:

• Normal variant:
• Chronic shunted hydrocephalus (case shown above):
• Longstanding anemia: Widening of the diploic space is due to marrow expansion from ineffective and excessive erythropoiesis. Seen in untreated severe congenital hemolytic anaemias (thalassaemia major, sickle cell anaemia), less commonly in patients with severe iron deficiency, cyanotic heart disease, osteopetrosis. The "hair-on-end" appearance is typical.
• Medications: Phenytoin is classic medication in this regard. Look for cerebellar atrophy. A case of G-CSF treatment causing a "hair-on-end" appearance has also been reported.
• Paget disease: Regions of sclerosis crossing sutures results in thickening of the diploic space ("Tam-O'-Shanter" skull, named after a Scottish hat that was named after a character in a poem of the same name by Robert Burns).
• Metabolic disorders: Renal osteodystrophy, hypoparathyroidism, and healing rickets
• Microcephaly: Skull overgrowth due to small brain.
• Osteopetrosis: Autosomal recessive form. CT in younger patients may show a high-attenuation inner table; a wide, low-attenuation diploic space, and a less high-attenuation outer table. "Hair-on-end" appearance can also be seen.

References

• Albert MH, Notheis G, Wintergerst U, Born C, Schneider K. "Hair-on-end" skull induced by long-term G-CSF treatment in severe congenital neutropenia. Pediatr Radiol. 2007 Feb;37(2):221-4. Epub 2006 Dec 21.
• Elster AD, Theros EG, Key LL, Chen MY. Cranial imaging in autosomal recessive osteopetrosis. Part I. Facial bones and calvarium. Radiology. 1992 Apr;183(1):129-35.
• Kattan KR. Calvarial thickening after Dilantin medication. Am J Roentgenol Radium Ther Nucl Med. 1970 Sep;110(1):102-5.
• Lucey BP, March GP Jr, Hutchins GM. Marked calvarial thickening and dural changes following chronic ventricular shunting for shaken baby syndrome. Arch Pathol Lab Med. 2003 Jan;127(1):94-7.
• Smith SE, Murphey MD, Motamedi K, Mulligan ME, Resnik CS, Gannon FH. From the archives of the AFIP. Radiologic spectrum of Paget disease of bone and its complications with pathologic correlation. Radiographics. 2002 Sep-Oct;22(5):1191-216.