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

Abstract: Background context: An extraforaminal disc herniation may present as a retroperitoneal mass and is thus a differential diagnosis for a malignant lesion. Purpose: 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. Study design: Case report. Methods: 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. Results: At surgery, an intraneural disc herniation was seen. Conclusions: 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. [Copyright &y& Elsevier]