% ▁for ▁girls ▁and ▁ 1 0 % ▁for ▁boys ▁younger ▁than ▁ 2 ▁months ▁at ▁the ▁time ▁of ▁diagn osis . ▁The ▁pel vic ▁site ▁of ▁the ▁primary ▁tum or ▁has ▁been ▁reported ▁to ▁be ▁an ▁ad verse ▁pro gn ost ic ▁factor , ▁most ▁likely ▁caused ▁by ▁a ▁higher ▁rate ▁of ▁incomplete ▁res ection . ▁In ▁older ▁children ▁and ▁adult s , ▁the ▁tum or ▁may ▁be ▁mistaken ▁for ▁a ▁p ilon idal ▁sin us , ▁or ▁it ▁may ▁be ▁found ▁during ▁a ▁rect al ▁exam ▁or ▁other ▁evaluation . ▁ ▁Di agn osis ▁ ▁During ▁pr en atal ▁ul tras ound , ▁an ▁S CT ▁having ▁an ▁external ▁component ▁may ▁appear ▁as ▁a ▁fluid - filled ▁c yst ▁or ▁a ▁solid ▁mass ▁stick ing ▁out ▁from ▁the ▁fet us ' ▁body . ▁ ▁F etal ▁S CT s ▁that ▁are ▁entirely ▁internal ▁may ▁be ▁und et ected ▁if ▁they ▁are ▁small ; ▁ ▁detection ▁( or ▁at ▁least ▁susp icion ) ▁is ▁possible ▁when ▁the ▁f etal ▁bl ad der ▁is ▁seen ▁in ▁an ▁ab normal ▁position , ▁due ▁to ▁the ▁S CT ▁pushing ▁other ▁org ans ▁out ▁of ▁place . ▁ ▁At ▁birth , ▁the ▁usual ▁presentation ▁is ▁a ▁visible ▁l ump ▁or ▁mass ▁under ▁the ▁skin ▁at ▁the ▁top ▁of ▁the ▁but to cks ▁cre ase . ▁ ▁If ▁not ▁visible , ▁it ▁can ▁sometimes ▁be ▁felt ; ▁g ently ▁pro dd ed , ▁it ▁feels ▁somewhat ▁like ▁a ▁hard bo iled ▁egg . ▁ ▁A ▁small ▁S