Surgical Management and Classification of Cerebellomedullary Angle Tumors in 90 Pediatric Patients: Importance of the Extended Suboccipital Approach

Introduction: Extent of resection (EOR) remains the most important determinant of long-term and progression-free survivals for most pediatric posterior fossa tumors. The lateral cerebellomedullary region harbors complex anatomical relationships, making it a common location for residual disease. Surgeons variably employ a multitude of midline and lateral approaches, and objective guidelines are lacking.

Methods: We reviewed preoperative MRI scans of 347 elective posterior fossa craniotomies performed at Le Bonheur Children’s Hospital between January 2010 and June 2018. We defined the lateral cerebellomedullary angle as the region involving the foramen of Luschka (FL) and/or the cerebellomedullary cistern (CMC). Tumors in that area were classified according to their extension: type 1 (FL), 2 (CMC), 3A (premedullary cistern, PMC), 3B (cerebellopontine angle, CPA) and 3C (all compartments). Demographic, preoperative, intraoperative, and postoperative data were recorded. The primary endpoints were extent of resection and any resultant surgical complications.

Results: Ninety patients met inclusion criteria, of which 37 (41%) had prior surgery with residual disease. There were 25 type 1 tumors, 23 type 2 and 42 patients with type 3 tumors. The majority was consistent with ependymoma (41; 45.5%), most of which were anaplastic of WHO grade III (80.4%), followed by medulloblastoma (24, 26.7%) and pilocytic astrocytoma (14, 15.5%). Type 2 and 3 tumors were more likely to be treated using an extended or a lateral suboccipital approach (p = 0.0455 and p = 0.0001, respectively). A retrosigmoid or far lateral approach was only used in 6 cases (6.6%). Combined with a dissection of the cerebello-medullary fissure, the extended suboccipital approach allowed for an appropriate exposure for these lateral-most tumors, except in 3. Residual disease on intraoperative and immediate postoperative MRI requiring reexploration was consistent with the anatomical type, and occurred more frequently in type 3 tumors (p = 0.043). Such imaging and reexploration strategy was helpful in achieving gross-total (GTR) or near-total resection (NTR) in 24 cases (26.7%). Final GTR or NTR was achieved in 81% of cases, with no intergroup difference, but group 3 had more postoperative cranial nerve (CN) deficits (p = 0.0003) and PEG-tube placement (p = 0.011).

Conclusion: Although modern research is shifting toward molecular and genomic subtyping, anatomical factors remain the most crucial determinant of EOR. Lateral cerebello-medullary tumors can be safely resected with good anatomical knowledge, microsurgical technique and intraoperative imaging. The extended suboccipital approach with CMF dissection is suited for pediatric tumors extending as far laterally as the CMC and CPA, and medially as the PMC.