Diagnostic Usefulness of Intraoperative Ultrasonography for a Thoracic Arachnoid Cyst

We present a case of an intradural arachnoid cyst that was successfully diagnosed via ultrasonography. It is challenging to distinguish between spinal arachnoid cysts and spinal cord herniations on preoperative computed tomography (CT) and magnetic resonance imaging (MRI). Additionally, these diseases have been reported to coexist. Therefore, a definitive diagnosis is not provided until intraoperative findings sufficiently exclude spinal cord herniation. Differentiating these two entities is vital from a surgical perspective. The treatment of spinal cord herniation requires the division of the dentate ligaments to allow rotation of the spinal cord for adequate inspection of the ventral cord and dura. To exclude spinal cord herniation, adequate exposure should be provided for arachnoid cysts. We experienced a case of an intradural arachnoid cyst that was successfully diagnosed via intraoperative ultrasonography. Making the correct diagnosis minimizes unnecessary surgical invasion by omitting the manipulation required to adequately visualize the ventral spinal cord for the exclusion of a spinal cord herniation.