Table 2 Salient features of benign skull lesions on CT and MRI

Fibrous dysplasia

Typically homogeneously sclerotic with “ground-glass appearance”.

Variable signal depending on amount of mineralised stroma and fibrous tissue. Most commonly hypointense on T1 and T2.

Osteoma

Juxta-cortical sclerotic lesion.

Hypointense T1, variable signal on T2 depending on amount of cortical and trabecular bone.

Langerhans cell histiocytosis

Lytic lesion with “bevelled edges”.

“Button sequestrum” may be present.

Variable signal, extensive marrow oedema is typically present.

Plus enhancement.

Osseous venous vascular malformation (formerly haemangioma)

Trabeculations, “sunburst pattern”.

“Bunch of grapes” appearance.

Diffuse enhancement.

Intraosseous meningioma

Sclerotic lesion.

Hyperostosis.

Hypointense T1, variable signal on T2.

Paget disease

Lytic phase: “osteoporosis circumscripta”.

Mixed phase (lytic and sclerotic): skull vault enlargement; “cotton-wool” appearance.

Blastic phase: bone thickening and sclerosis.

Lytic phase: hyperintense T2, hypointense T1 (with foci of interspersed T1 hyperintense yellow marrow).

Mixed phase: yellow marrow maintained in all sequences.

Blastic phase: Hypointense T1 and T2.

Calvarial sarcoidosis (usually multiple)

Lytic.

Well-demarcated margins.

Variable signal, may enhance.

Can have periosseous soft tissue component.

Ossifying fibroma

Expansile, lytic lesion or solid lesion with areas of cystic changes.

Solid component is isointense on T1 and iso/hypointense on T2.

Heterogeneous enhancement of the solid component.

Epidermoid cyst

Well-demarcated osteolytic lesion with sclerotic margins.

Remodelling and expansion of skull tables.

Restricted Diffusion.

Do not enhance.

Dermoid cyst (typically midline near anterior fontanelle)

Expansile osteolytic lesion.

Can have soft tissue component.

Fatty signal on T1, variable signal on T2.

May see peripheral enhancement.