L5-S1 extraforaminal intraneural disc herniation mimicking a malignant peripheral nerve sheath tumor

An extraforaminal disc herniation may present as a retroperitoneal mass and is thus a differential diagnosis for a malignant lesion.

To highlight the difficulty in the accurate preoperative differentiation between an extraforaminal disc herniation and a malignant retroperitoneal mass despite the use of advanced anatomical and metabolic imaging.

Case report.

The authors present a case of a 55-year-old man, with a family history of neurofibromatosis, who presented to us 2 months after the insidious occurrence of severe, unrelenting, right-sided, L5 dermatomal pain. He subsequently developed rapidly progressive motor weakness in the same myotome, which caused a foot drop. On examination, his straight-leg raise test was normal. Magnetic resonance imaging demonstrated a peripherally enhancing, complex, cystic mass continuous with the L5 nerve, displacing its fascicles medially, as it descended over the right sacral ala. A positron emission tomography scan demonstrated increased radiotracer uptake. The clinicoradiologic presentation was that of a malignant peripheral nerve sheath tumor.

At surgery, an intraneural disc herniation was seen.

Several pitfalls exist in establishing the uncommon diagnosis of an extraforaminal disc herniation. This entity occurs ventrally and must remain a consideration when elaborating the differential diagnosis of a retroperitoneal mass in close proximity to the vertebral column.