Spontaneous resolution of acquired tonsillar herniation caused by isolated cerebellar tonsil inflammation: case...

Chiari I malformation is a well-known disease involving caudal descent of the cerebellar tonsils and is generally considered to be a congenital condition. Acquired Chiari I malformations as a result of various causes are well described. An unusual case is reported in which regression of an acquired Chiari I malformation caused by isolated cerebellar tonsil inflammation in a patient with infectious mononucleosis was observed after conservative treatment. This supports the view that the cause of tonsillar herniation should be considered as an important factor in patient selection for surgical decompression.

A 6-year-old boy presented with a 1-week history of progressive occipital headache, neck pain, and dysequilibrium. A neurological examination revealed hyperreflexia in all extremities; he also had a fever, pharyngitis, and cervical adenopathy. A magnetic resonance imaging study demonstrated isolated right cerebellar tonsil enhancement and herniation into the foramen magnum. Further laboratory findings disclosed Epstein-Barr virus infection.

The patient underwent conservative treatment for systemic illness, and he was asymptomatic after 3 weeks. A follow-up magnetic resonance imaging study obtained 2 months after discharge demonstrated resolution of the tonsillar herniation.

Because the patient presented with infectious mononucleosis and cerebellar tonsillar herniation, direct treatment of decompression was considered unnecessary. Thus, caution in patient selection for surgical treatment is suggested in such unique cases.