"Scalpel sign" in spine pathology: Presentation in three rare different diagnoses.

Abstract. Background The “Scalpel sign” is a radiological finding observed on sagittal MRI and CT myelographic images, corresponding to an indentation in the dorsal aspect of the spinal cord, resembling a surgical scalpel blade. It is said to be a pathognomonic imaging discovery linked to dorsal arachnoid webs (DAWs). However, other spine-related conditions may mimic DAWS on MRI such as arachnoid cysts (SAC) or ventral herniation (VSCH), inducing misdiagnosis. Methods We present a retrospective review of cases involving these three different diagnoses presented in our institution in the last 5 years that share in common the characteristic focal dorsal indentation of the spinal cord. Results 7 cases were identified, all but one treated and confirmed intraoperatively. All of them were located at the dorsal spinal cord. MRI was the study of choice for evaluation. Clinical manifestations included back pain and lower extremity numbness and weakness together with compressive myelopathy signs and urinary symptoms. Mean follow up was 16.8 months with satisfactory postoperative results. Conclusion Isolated radiological presentation of the scalpel sign is not sufficient to distinguish between dorsal arachnoid webs, arachnoid cysts and ventral herniation of the spine. However, awareness of its importance is relevant for accurate curative surgical planning.