Sacrococcygeal dimple: new classification and relationship with spinal lesions

This study aims to ascertain which specific types of sacrococcygeal dimples are associated with underlying spinal cord malformations.

From 2008 to 2011, we prospectively examined children less than 2 years old with sacrococcygeal dimples. Each patient underwent clinical assessment of dimples and magnetic resonance imaging. We devised the following new classification of dimples according to their location: type 1, dimples located within the gluteal crease, including coccygeal pits; type 2, dimples located at the upper edge of the gluteal crease with associated curving or deformity of that crease; and type 3, dimples located well above the gluteal crease.

We evaluated 142 patients with sacrococcygeal dimples. Although we identified spinal malformations such as spinal lipomas, filum cysts, and thickened fila terminalia in only 17 % of infants with type 1 dimples, we observed them in 45 % with type 2 and 55 % with type 3. Thus, in terms of the rate of spinal malformations, there are significant differences between types 1 and 2 and between types 1 and 3.

We propose a new classification of sacrococcygeal dimples. Although type 2 dimples have previously been classified as simple dimples that require no further investigation, we have identified that they are strongly associated with spinal deformities, comparable to atypical type 3 dimples. Thus, both types 2 and 3 dimples warrant radiological investigation.