Quote from "Pediatric Surgery (Springer Surgery Atlas)" by Prem Puri, Michael E. Höllwarth -

"Dermal sinuses must be differentiated from benign coccygeal pits, which end blindly and never extend intraspinally, and therefore do not require further imaging evaluation or treatment. Dermal sinus tracts are found above the natal cleft and are usually directed superiorly. By comparison, coccygeal pits are found within the natal cleft, below the top of the intergluteal crease, with a tract extending either straight down or inferiorly. Coccygeal pits occur over the lower sacrum and coccyx and are anatomically located below the level of the subarachnoid space. They are encountered in nearly 5% of newborns, and although they are present from birth, they rarely manifest themselves before adult life. In later years, these small pits or dimples may become pilonidal sinuses or abscesses."