T1 pre-gad T2 FSE T2 FSE

Diagnosis: Intradural thoracic arachnoid cyst

Spinal arachnoid cysts are uncommon lesions. One series from Children's Hospital in Los Angeles published in 1992 looked at 11 pediatric patients age 19 months to 18 years of age with spinal arachnoid cyst. The most common location was in the thoracic spine followed by a cervicothoracic and lumbar then the cervical spine and sacrum. Most of the arachnoid cysts were intradural (8/11). Half of the patients have associated myelomeningocele, while one had a diastematomyelia. For the most part, the patients presented with a progressive myelopathic picture. Treatment consisted of fenestration of the cyst and/or resection of the wall of the cyst or shunting from either the cyst to the pleural space or the cyst to the subarachnoid space.

On imaging, spinal arachnoid cysts have CSF signal characteristics and if small may be difficult to differentiate asymmetry in the sizes of the ventral vs. dorsal subarachnoid spaces. Communication of arachnoid cysts with the subarachnoid space may be demonstrated on CT myelography if the lesion is intradural. A late finding may be cord atrophy from the progressive mass effect of the arachnoid cyst. In this case, the phase contrast cine MR was diagnostic since it demonstrated that the tiny residual subarachnoid space has different flow characteristics than the CSF within the arachnoid cyst. At surgery, an intradural arachnoid cyst was found and was treated with cysto- peritoneal shunt.

Rabb CH, McComb JG, Raffel C, et al. Spinal arachnoid cysts in the pediatric group: an association with neural tube defects. J Neurosurg, Sep 1992; 77(3):p369-72.

Mirich DR, Hall JT, Carasco CH. MR imaging of traumatic spinal arachnoid cyst. J Comput Assist Tomogr, Sep-Oct 1988; 12(5):p862-5.