Plexiform neurofibroma is a benign proliferation of peripheral nerves, pathognomonic of neurofibromatosis type 1 (NF1), of which this patient had a history. 

It affects neural plexuses and multiple medium or/and large caliber branches of nerves, generating large fusiform and tortuous masses.

It can be seen in 16-40% of patients with NF1 affecting any organ. However, intra-abdominal or retroperitoneal localization is very rare.

MRI typical findings include hypointense T1 structures; in T2-weighted images ring-like structures with high T2 signal in the periphery correspond to myxoid matrix, and low central T2 signal represents collagen and fibrous tissue (target-sign). The areas of low T2 signal have mild enhancement following gadolinium administration.

MRI is the best choice for the medical study and follow-up of neurofibromas since they can become malignant in 2-5% of cases. This fact should be suspected when persistent pain, increasing mass size and border irregularity are present.