Gross and neurosurgical anatomy of the cerebellar tonsil

Introduction The primary purpose of this review was to focus on the gross anatomy, including morphometric characteristics and arterial vasculature, of the human cerebellar tonsil. We also aimed to investigate the neurosurgical anatomy of this clinically important structure of the human brain. Discussion The cerebellar tonsil is a rounded lobule on the undersurface of each cerebellar hemisphere, continuous medially with the uvula of the cerebellar vermis and superiorly with the flocculonodular lobe. Arterial branches entering the tonsil originate not only from the posterior but from the anterior inferior cerebellar artery as well, often anastomosing with those from the posterior. The main clinical conditions able to affect the position of the cerebellar tonsil include raised intracranial pressure, myelomeningocele, Chiari malformations, posterior fossa hypoplasia and Idiopathic scoliosis. The main neurosurgical approaches related to the region of the cerebellar tonsil include the transcerebellomedullary fissure approach, the tonsillouveal fissure approach (telovelar approach), the lateral approach to the fourth ventricle, the supraand subtonsillar approaches, the median and farlateral suboccipital approaches. Conclusion The position of the cerebellar tonsil can be affected in some congenital and acquired disorders including Chiari malformations and raised intracranial pressure. The high incidence of tonsillar arterial supply of single origin, partially explained by vascular anomalies such as arterial hypoplasticity, makes this structure potentially vulnerable to vascular accidents (mainly infarcts) of the inferior cerebellar arteries. A thorough understanding of the regional tonsillar anatomy, as well as its relations with the branches of the posterior inferior cerebellar artery is of paramount significance for neurosurgical interventions in this area.