Surgical anatomy of the cerebellar tonsils: A cadaveric study

Knowledge of the normal anatomy of the cerebellar tonsils is a prerequisite in various surgeries of the posterior cranial fossa Clinical conditions, as the Chiari I malformations (CIM) alter the normal position of the cerebellar tonsils.

Therefore, we aim to better elucidate the surgical anatomy of and around the cerebellar tonsils in regard to the CIM.

Fifty formalin-fixed adult cadavers injected with colored latex through vertebral arteries underwent craniotomy and durotomy to expose the cerebellar tonsils and related structures. The tonsils and their surrounding anatomy were then studied.

Forty cerebellar tonsils were at or above the foramen magnum. Five specimens presented with CIM with the tonsils below (3-5 mm) the FM with a mean tonsillar decent of 7.9 ± 2.3 mm. Of the cadavers without CIM, in forty-two cases, the thickness of the dura mater was within ±3SD ranges. In three cases, the dura mater was thinner at the CVJ and one case; the dura adhered tightly to the inner aspect of the occipital squama. In five CIM cadavers, the dura mater was markedly thicker at the CVJ. The PICA caudal loop was 5.9 ± 1.6 mm long. In CIM cases, the PICA loop was longer, nearer the dura, 1 mm below the superior border of the C1 posterior arch. The distances from the PICA loop were markedly reduced by 3 mm from the spinal accessory nerve and 2 mm from the first spinal nerve. The DN was significantly closer to the tonsillar peduncle in CIM cases.

These data are important for better understanding the intrinsic and extrinsic anatomy of the cerebellar tonsils in patients with and without CIM. Importantly, tonsillectomy/tonsillar coagulation must consider the close relationship of the dentate nucleus to the base of the cerebellar tonsil to avoid iatrogenic injury.