Fig. 3.

Transitional lipoma. A : Left : sagittal MRI shows lipoma begins dorsally but involves entire conus. Ventral side of neural placode is free of fat. Right : the plane of the fusion line begins dorsally then cuts obliquely towards the tip of the conus. The array of DREZ and dorsal roots is also forced to slant dorso-ventrally. B : Intraoperative picture showing massive lipoma but very distinct dorso-ventral fusion line separating fat from the DREZ and dorsal roots, which always lie lateral and ventral to the fusion line. The ventral side of the placode is always free of fat in a regular transitional lipoma. C : Top : idealised drawings of pre- and post-resection of a relatively “standard” transitional lipoma, along an asymmetrical and oblique plane bound by the fusion line on each side, over an occasionally undulating lipoma-cord interface. Bottom shows pre- and post-resection intraoperative pictures. Reprinted from Pang et al. [61] with permission from Springer Nature. MRI : magnetic resonance imaging, DREZ : dorsal root entry zone.