Intradiploic epidermoid cyst

Intradiploic epidermoid cysts refer to epidermoid cysts that occur in the diploë of the skull.

Clinical presentation

Painless slowly progressive scalp swelling.

Pathology

• epidermoid cysts may be congenital (most common, arising from ectodermal inclusion during neural tube closure and subsequently remain within the cranial bones) or acquired (e.g. post-surgical or post-traumatic implantation) ⁴

• intradiploic epidermoids are less frequent than the intradural variety ¹

Radiographic features

Intradiploic epidermoids occurs within the frontal, parietal, occipital and sphenoid bones, as well as the spine ¹.

Plain radiograph

• rounded or lobulated area of bone destruction, well-delineated sclerotic scalloped margins

CT

• non-enhancing hypodense lesion with sharply demarcated bony defects and zones of calcifications

• it may alter the outer and/or inner tables of the skull (the inner table more than the outer)

MRI

• T1: slightly hyperintense to the CSF

• T2: isointense/hyperintense to the CSF

• FLAIR: hyperintense to the CSF space

• DWI: restricted diffusion with characteristic hyperintensity

• T1C+: none

History and etymology

The first intradiploic epidermoid cyst was reported by J Müller in 1838 ⁵.

The radiological pattern of intradiploic epidermoids was first described by Cushing in 1922.

Differential diagnosis

Consider:

• eosinophilic granuloma

• calvarial hemangioma

• dermoid cyst

• fibrous dysplasia