Trans-Cerebellomedullary Fissure Approach for Fourth Ventricular Tumors, Outcome Analysis in Thirty Consecutive Cases

Background: The use of anatomical clefts in the cerebellomedullary fissure to approach the fourth ventricle eliminates violation of neural tissue. The median inferior sub-occipital approach along the “tonsilouveal” sulcus to treat fourth ventricle lesions was described. The approach through the cerebellomedullary fissure to the tela choroidea and inferior medullary velum provides an additional means to access the fourth ventricle and has been used by an increasing number of neurosurgeons. Objective: Evaluation of the efficacy of using the natural clefts in the posterior fossa through understanding the microsurgical anatomy of this region instead of violating functioning neural tissues and preservation of vascular structures. Planned total removal of the tumors is our aim, and if not possible, the maximum amount of tumor tissue to be removed with minimal morbidity. Patients and Methods: The study included thirty patients. All of them were subjected to history taking, complete neurological examination and imaging. Total tumor removal was the main surgical strategy. The uvulotonsillar and medullotonsillar spaces on both sides were opened along with the lateral and deep dissection around the surfaces of the tonsil and the biventral lobule without dividing any neural tissue, thus, overcoming the drawbacks of trans-vermian approach. Results: All of our patients suffered from preoperative hydrocephalus and large tumor volume sufficient to obstruct the cerebrospinal fluid (CSF) pathways. We resorted to perform CSF diversion procedure in a total of twenty three patients. We were in need for upper cervical laminectomy in 14/30 (47%) due to both tonsillar herniation and tumor descent. Gross total resection could be achieved in 23/30 (77%). Transient post-operative mutism occurred in 4/30 (13%), while transient oral-pharyngeal apraxia occurred only in one patient (3%). The outcome according to Karnofsky scale was 100 in 20/30 (66.7%), 90 in 4/30 (13.3%), 80 in 2/30 (6.6%), 70 in 2/30 (6.6%) and 10 in 2/30 (6.6%). Conclusion: Pre-operative CSF diversion is safe. The telovelar approach provides adequate surgical exposure of the floor of the fourth ventricle and additional access to the superolateral recess with only a limited decrease in working angles when approaching the rostral portion of the ventricle. Preservation of the posterior inferior cerebellar artery (PICA) is so important. Full exposure could be achieved without removal of or incision through the neural tissue of the cerebellum and good quality of life and complete cure became possible.