Mixed composition, heterogeneous on all sequences, with cystic areas that conflate giving it the appearance of a "bag of worms".
Origin at the right vertebral conjunction orifice level T11-T12, covering from T10 to L1 level. It extends through the fascia of the erector muscle of the back and quadratus lumborum, conditioning the volume effect that displaces psoas muscle, posterior para-renal space and crura, in addition, associated bone remodelling is observed,