Spanish term (edited): anillo ligamentario y constrictor

Bands of meningeal tissues (dural or arachnoid) may develop in syringomyelia/Arnold-Chiari malformation. I don't think it is an anatomical ligament or membrane that needs to be excised, but rather these (pathological) bands which impede CSF circulation and enhance associated symptoms. I have never heard of (explicitly) "circular bands" and can't find references for this term, but it should be vague enough to cover the source text without being too specific in a wrong direction.

Some reference describing the neurosurgical procedure for Arnold-Chiari:

"Various authors have recommended that to achieve maximal decompression, it is necessary to open the dura mater and to cut all constrictive dural and arachnoidal bands."
http://www.neurologyindia.com/article.asp?issn=0028-3886;yea...

"We routinely microsurgically divide the tense arachnoid bands that have grown to hold the herniated Cerebellar Tonsils to the inside of the Dura Mater in the Foramen Magnum region and in the upper Cervical Spinal Canal. Once this is accomplished, we routinely microsurgically separate the Cerebellar Tonsils, in the midline, free up these arachnoidal band-like attachments to the upper Cervical Spinal Cord"
http://www.neurosurgerydallas.com/4_4_17.php