Small Thoracic Disk Herniation without Spinal Stenosis Presenting with Acute Myelopathy: Three Case Reports

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We herein describe three patients with thoracic disk herniation (TDH) that presented with acute myelopathy at the Tokyo Metropolitan Neurological Hospital between 2014 and 2021 (age range, 45-76 years; male/female ratio = 1:2), with a focus on the mechanisms underlying their development. All patients had sudden-onset gait disturbance due to acute nontraumatic paraparesis. The specialties of the doctors at the first hospital were neurology and orthopedic surgery. TDH was overlooked at the first hospital, and the patients were referred to our hospital. The TDH in all cases was of the central type; however, since they were small, no spinal stenosis was observed. The key feature of all three cases is the small anterior deformation of the spinal cord, making a vascular etiology for the symptoms more plausible than a compressive etiology. After a follow-up of several months or years, two out of three patients underwent surgery with the use of the transfacet pedicle-sparing approach due to residual symptoms. Intraoperative ultrasonography showed that the spinal cord was anchored to TDH by the dural attachment of dentate ligaments. The physical relationship between the dentate ligaments and TDH may be associated with the vascular cause of the symptoms of small TDH.