Case History: 40-year-old man with low back pain, right lower extremity paraesthesias, and incontinence. He presents 10 days later with worsening pain.

The initial lumbar spine MRI shows a T1 isointense intradural extramedullary mass at the level of T11/T12 causing moderate cord compression. The mass is well circumscribed and solid, with a cystic central component. The mass has avid enhancement on post-gadolinium imaging. These findings are most consistent with a schwannoma, and this mass was pathologically proven to be a schwannoma after resection.

On the lumbar spine MRI 10 days later, the mass demonstrates mobility. The mass is now at the level of T12/L1, previously T11/T12. The later coronal images show a clockwise rotation of the mass, which is more horizontally oriented on the subsequent MRI. The imaging finds are consistent with a mobile schwannoma.

Mobile intradural extramedullary masses are a rare entity, schwannomas being the most common tumor types. Schwannomas are a benign tumor comprised of the cells of the peripheral nerve sheath. Mobile intradural extramedullary schwannomas have a male predominance with mean age of 49. These patients present with symptoms of cord and nerve root compression, including weakness, back pain, radiculopathy, gate disturbance, or incontinence. The most common location is the lumbar (65%), thoracolumbar (15%), thoracic (10%) spine, followed by thoracocervical (5%) and cervical (5%) spine. Symptoms have been noted to be position related, exacerbated by Valsalva maneuvers and relieved by laying supine. The mobility of the schwannomas may be associated with changes in intradural pressure, such as after myelography. Mobility of the tumor may pose a challenge to locating the tumor during surgery, which can be resolved by using intraoperative ultrasound.

1. Lee, Dong Yeob, and Hoon Jae Chung. "Mobile schwannoma of the cauda equina diagnosed by magnetic resonance imaging and magnetic resonance myelography: A case report and review of the literatures." 

2. Kim, Soo-Beom, Hyung-Seok Kim, Jee-Soo Jang, and Sang-Ho Lee. "Mobility of intradural extramedullary schwannoma at spine: report of three cases with literature review." 

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