Impacted cisterna magna without syringomyelia associated with lancinating headache, throbbed nuchal pain and paraparesis treated byposterior fossa decompression.

A 29-year-old woman with acute lancinating headache, throbbed nuchal pain and subacute paraparesis underwent brain MRI in supine position that depicted: the absence of the cisterna magna, filled by non herniated cerebellar tonsils and compression of the brain stem and cisternae of the posterior fossa, which are aspects of the impacted cisterna magna without syringomyelia and without hydrocephalus. During eight days, pain was constant and resistant to drug treatment. Osteodural-neural decompression of the posterior fossa, performed with the patient in sitting position, revealed: compression of the brainstem, fourth ventricle and foramen of Magendie by herniated cerebellar tonsils, which were aspirated. Immediately after surgery, the headache and nuchal pain remmited. MRI depicted the large created cisterna magna and also that the cerebellar tonsils did not compress the fourth ventricle, the foramen of Magendie and the brainstem, besides the enlargement of posterior fossa cisternae. Four months after surgery, headache, nuchal pain and paraparesis had disappeared but hyperactive patellar and Achilles reflexes remained.