Signal intensity patterns in intraspinal dermoids and epidermoids on MR imaging

Retrospective evaluation of MR images of nine intraspinal dermoid (n=4) and epidermoid (n=5) tumours was undertaken. T1-weighted images were available in all the patients while proton density (PD) and T2-weighted images were available in seven patients. Except for one lesion (only T1-weighted images were available in this case), all the lesions were clearly delineated on MR images. Most (5 out of 7) were better appreciated on T1- and PD-weighted images than on T2-weighted images. On T1-weighted images, the epidermoids were either isoto mildly hypointense to the cord (n=3), isointense to CSF (n=1) or markedly hyperintense (n=1). On the PD images, the epidermoids were either isointense to cord (n=3) or markedly hyperintense (n=1). All the lesions were iso-to hyperintense to CSF on T2-weighted images. Of the four dermoids three showed a mixed intensity pattern on all sequences; the dominant component gave short T1 and short T2 values, consistent with fat. The fourth lesion showed homogenous material with a signal intensity intermediate between that of CSF and cord on T1-weighted images. Dermal sinus tracts were present in four of the nine patients; three patients had an intraspinal component. This study shows that although MR imaging is excellent for their detection, it cannot differentiate the two tumour types.