Intradiploic Arachnoid Cyst Identified by Diffusion-Weighted Magnetic Resonance Imaging. Case Report.

Abstract

A 72-year-old woman presented with an intradiploic arachnoid cyst in the occipital intradiploic space which was found incidentally by magnetic resonance (MR) imaging. Computed tomography revealed a widened diploic space and thinning of the inner and outer tables of the occipital bone. The cyst appeared as isointense to the cerebrospinal fluid on both T 1 -and T 2 -weighted images. The differential diagnosis of intradiploic epidermoid cyst could be excluded because the lesion was low intensity on diffusion-weighted MR images. Arachnoid cyst is a benign lesion, so exploratory surgery should be avoided unless the cyst is symptomatic. Diffusion-weighted MR imaging is an effective modality to distinguish diploic epidermoid cysts from arachnoid cysts.

Congenital intradiploic arachnoid cyst presenting as painless proptosis

“…[1][2][3][4][5][6][7][8][9] These nontraumatic cystic lesions are presumed to be congenital, with CSF pulsating through a dural defect into the intradiploic space and leading to gradual enlargement with thinning of the inner and outer tables of bone. 1 Given the low pressure of CSF pulsations, Thomas and Rout 1 speculated that the lesions must be initiated before ossification of the cranium because normal CSF pressure would not likely cause intradiploic expansion in otherwise intact bone.…”

“…In our case, the diffusionweighted images were degraded by artifact from the patient's orthodontic braces; however, there was no gross increased signal intensity on these pulse sequences or peripheral enhancement, as might be expected if the lesion was an epidermoid cyst. 8 An epidermoid cyst would also be observed in this setting; however, follow-up may vary because it may progress at a faster rate than an intradiploic arachnoid cyst.…”

Intradiploic epidermoid cyst with focal internal enhancement

“…In such a case, its diffusion characteristics may be useful for differentiating beween the two as reported for the differential diagnosis of cerebellopontine angle lesion; the epidermoid cyst should have lower molecular diffusion than the arachnoid cyst even in the diploic space. 12,13 Although a dermoid cyst that lacks evidence of a fat component on CT or MR imaging is virtually indistinguishable from an epidermoid cyst, its distinction would not be clinically worthwhile, as their management is essentially the same.…”

Skull base: pseudolesion or true lesion?

“…In such situations, diffusion-weighted imaging might be beneficial for the differential diagnosis (Fig. 17) [25]. Fig.…”