1. Case of the Week 90 Young adult male with previous low back pain brings his MRI in for a second opinion. He was told that there was nothing to worry about.

2. What is the most significant abnormality present? What is the clinical significance? T 1T 2

3. Answers Most significant abnormality: Most significant abnormality: An oval cystic lesion is present in the spinal canal, posterior to S1-2. It has low signal intensity on T1-weighted images and high signal intensity on T2, the same as the cerebral spinal fluid. An oval cystic lesion is present in the spinal canal, posterior to S1-2. It has low signal intensity on T1-weighted images and high signal intensity on T2, the same as the cerebral spinal fluid. Clinical Significance: Clinical Significance: This is a classic Tarlov cyst (aka perineural sacral cyst). These are congenital diverticula of the spinal nerve root sleeves and are usually of no significance. When large they may cause pressure erosion of the posterior aspect of the sacrum. Rarely neurological symptoms may result, requiring surgical excision. This is a classic Tarlov cyst (aka perineural sacral cyst). These are congenital diverticula of the spinal nerve root sleeves and are usually of no significance. When large they may cause pressure erosion of the posterior aspect of the sacrum. Rarely neurological symptoms may result, requiring surgical excision.