Expanding the reach of the trans-middle cerebellar peduncle approach: pontine cavernous malformations, tissue transgression beyond the safe entry zone, and the invisible triangle.

OBJECTIVE: In the authors' microsurgical experience, the trans-middle cerebellar peduncle (MCP) approach to the lateral and central pons has been the most common approach to brainstem cavernous malformations (BSCMs). This approach through a well-tolerated safe entry zone (SEZ) allows a wide vertical or posterior trajectory, reaching pontine lesions extending into the midbrain, medulla, and pontine tegmentum. Better understanding of the relationships among lesion location, surgical trajectory, and long-term clinical outcomes could determine areas of safe passage. METHODS: A single-surgeon cohort study of all primary trans-MCP BSCM resections was conducted from July 1, 2017, to June 30, 2021. Preoperative and postoperative MR images were independently reviewed by 3 investigators blinded to the intervention, using a standardized rubric to define BSCM regions of interest (ROIs) involved with a lesion or microsurgical tract. Statistical testing, including the chi-square test with the Bonferroni correction, logistic regression, and structural equation modeling, was performed to analyze relationships between ROIs and clinical outcomes. RESULTS: Thirty-one patients underwent primary trans-MCP BSCM resection during the study period. The median age was 50 years (IQR 24-49 years); 19 (61%) patients were female, and 12 (39%) were male. Seven (23%) patients had familial cavernous malformation syndromes. The median follow-up was 9 months (range 6-37 months). At the last follow-up, composite neurological outcomes were favorable: 22 (71%) patients had 0 (n = 12, 39%) or 1 (n = 10, 32%) major persistent deficit, 5 patients (16%) had 2 deficits, 2 (7%) had 3 deficits, and 1 patient each (3%) had 4 or 6 deficits. Unfavorable composite outcomes were significantly associated with lesions (OR 7.14, p = 0.04) or surgical tracts (OR 12.18, p < 0.001) extending from the superior cerebellar peduncle (SCP) into the contralateral medial midbrain. The ipsilateral dorsal pons was the most frequently implicated ROI involving a surgical tract and the development of new postoperative deficits. This region involved the rhomboid pontine territory and transgression of the pontine tegmentum (OR 7.53, p < 0.001). Structural equation modeling supported medial midbrain and pontine tegmentum transgression as the primary drivers of morbidity. CONCLUSIONS: Trans-MCP resection is a safe and effective treatment for BSCMs, including lesions with marked superior or inferior ipsilateral extension. Two trajectories are associated with increased neurological risk: first, a superomedial trajectory to lesions extending into the midbrain that transgresses the SCP, its decussation, or both; and second, a posteromedial trajectory to lesions extending into the pontine tegmentum. The corticospinal tract, SCP, and pontine tegmentum form an invisible triangle within the pontine white matter tolerant of transgression. When the surgeon works within this triangle, most deep pontine BSCMs, including large lesions, those with contralateral or posterior extension, and others extending into the midbrain and medulla, can be resected safely with the trans-MCP approach.

Experience and Balance: Long-Term Trends in Preferred Skull Base Approach for a Case Series of Cavernous Malformation Resections.

BACKGROUND: Skull base approaches are a foundation of modern cerebrovascular surgery; however, their application over time has varied. OBJECTIVE: To assess trends in skull base approach selection for cavernous malformation (CM) resection. METHODS: This is a retrospective case series of all first-time CM resections by a single surgeon from 1997 to 2021. Cases were classified by craniotomy and approach. Four sets of common comparator skull base approaches were identified by coauthor consensus: pterional and orbitozygomatic; retrosigmoid, extended retrosigmoid (xRS), and far-lateral; suboccipital and torcular; and trans-cerebellar peduncle (MCP) and transcerebellopontine angle. Counts were binned by 5-year or 10-year clusters for descriptive statistical assessment of temporal trends. RESULTS: In total, 372 primary CM resections met the study criteria and were included. Orbitozygomatic approach use increased during the second 5-year period, after which the pterional approach rapidly became and remained the preferred approach. During the first two 5-year periods, the far-lateral approach was preferred to the retrosigmoid and xRS approaches, but the xRS approach grew in popularity and accounted for >50% of operations in this comparator group. Trans-MCP use compared with the transcerebellopontine angle approach closely mirrored the change in xRS use. The midline suboccipital approach accounted for a larger proportion (range, 62%-88%) of cases than the torcular approach (range, 12%-38%) across all periods. CONCLUSION: The xRS and trans-MCP approaches have been increasingly used over time, while the orbitozygomatic and far-lateral approaches have become less common. These trends seem to reflect versatility, efficiency, and safety of these techniques.