Spinal arachnoid web is a rare condition that causes various neurological symptoms due to direct spinal cord compression by a thickened arachnoid membrane and subsequent cerebrospinal fluid (CSF) flow blockage, occasionally leading to presyrinx, which may precede syringomyelia. Magnetic resonance imaging (MRI) is helpful for establishing diagnosis. Although the “scalpel sign” is considered a characteristic finding, the arachnoid web is a fine lesion that is often difficult to visualize.

  We have described a case of a 63-year-old woman with complaints of progressive numbness in both her upper and left lower limbs for 10 years and progressive right axillary and upper back pain.

  MRI at the previous hospital revealed an intramedullary hypersignal lesion at the T2 level. Heavy T2-weighted sagittal imaging and cine-mode MRI performed at our hospital revealed the “scalpel sign” and a membrane-like structure that was impeding CSF flow on the dorsal side of the spinal cord. She was diagnosed with a spinal arachnoid web ; hence, T1-3 laminectomy was performed to remove arachnoid.

  Postoperatively, her neurological symptoms improved remarkably. Her numbness decreased, and the right axillary and back pain disappeared. Furthermore, the “scalpel sign” and intramedullary hypersignal lesion had disappeared. Postoperative cine-mode MRI revealed an improvement in CSF flow. Pathological examination of the resected arachnoid membrane showed normal tissue without any evidence of inflammatory or malignant lesion.

  Here, we have reported a case of arachnoid web with presyrinx, a reversible intramedullary lesion. The arachnoid web must be identified as a cause of presyrinx. Even in cases with a long course, surgical treatment should be considered to improve the presyrinx state and ameliorate the neurological condition.