Typical sacral dimples are <5mm in diameter, within 25mm of anus and located in midline. Rate of spinal dysraphism (bifida occulta) less than 1%.
Higher risk if do not fulfill these criteria. Lipomas, deviated/bifurcated crease are the most likely to be associated with dysraphism. Otherwise you expect at least 2 or more cutaneous markers (hair tuft, haemangioma, Mongolian spot, skin tag/tail).
Reports of high frequency of hair tufts in diastematomyelia probably refer to more striking lesions (“faun tails”).
Royal College of Radiology has policy – ignore sacral dimples unless atypical, or in combination with other lesions.
USS if neonate, but MRI if US abnormal or equivocal, where neurological signs (bladder, bowel, lower limb) or lesion discharging.[Arch Derm 2004]