POSITION OF CEREBELLAR TONSILS IN REFERENCE TO FORAMEN MAGNUM: AN MRI STUDY.

Corresponding Author:
Dr. A. S. Lakshmi,
Additional Professor,
Department of Anatomy,
Medical College, Trichur-680596, Kerala.
E-mail: lakshmipadmanabhanblr@gmail.com

ABSTRACT: Normal position of the cerebellar tonsils is described to be at or above the foramen magnum. Western studies have shown the cerebellar tonsils to be below the foramen magnum. Position of tonsils is of great importance in assessing the hind brain deformity–Chiari malformation. There are no Indian studies to corroborate the findings. Hence, we proposed a basic study to find out the existence of tonsillar ectopia (Position of tonsils below the foramen magnum) in normal population. Our study was conducted for a period of 8 months at the Radiology Department of SCTIMST, Trivandrum, Kerala; 515 patients with normal brain, spinal cord and normal craniovertebral junction (CVJ) were selected from a group of patients who underwent MRI investigation of brain and cervical spine for various vague complaints. They ranged from 2 months to 80 years and of both sexes. Patients with raised intracranial tension and established CVJ anomalies were excluded. The study was done on the MR images obtained on the MR monitor directly during the scan. Foramen magnum and the inferior extent of cerebellar tonsils were marked. The position of the tonsils was noted in reference to foramen magnum and the data analysed. Tonsillar ectopia was noticed in 21% of the population. A downward descent in the position was observed in the fifth decade of life. In infancy and old age, higher positions were noted. The study indicates that the position of the tonsils below the foramen magnum is a normal occurrence.

KEYWORDS: Foramen Magnum, Brain, Cerebellar Tonsils, Chiari Malformation.