Main Session
Sep 29
PQA 03 - Central Nervous System, Professional Development/Medical Education

2664 - Signals in the Shadows: Structural Imaging and Electrophysiological Insights in Optic Nerve Schwannoma Adjuvant Therapy

08:00am - 09:00am PT
Hall F
Screen: 2
POSTER

Presenter(s)

Vangipuram Shankar, MD, MBBS Headshot
Vangipuram Shankar, MD, MBBS - Apollo Proton Cancer Centre, Chennai , Tamil Nadu

V. Shankar1, S. Ghosh2, S. Cholayil1, D. Arjundas3, S. Paramasivan4, and V. Sai Shreya5; 1Apollo Cancer Centers, Chennai, India, 2Dept. of Neurosurgery, Apollo Proton Cancer Center, Chennai, India, 3Chief Neurologist, Mercury Hospital, Chennai, India, 4Dept. of Neurosurgery, Apollo Hospitals, Greams Unit, Chennai, India, 5ACSR Govt. Medical College, Nellore, India

Purpose/Objective(s): Optic nerve schwannomas (ONS) are rare tumors with limited evidence-based management guidelines. This study evaluates the utility of Visual Evoked Potential (VEP) & Optical Coherence Tomography (OCT) in stratifying adjuvant therapy—Stereotactic Radiosurgery (SRS) versus Fractionated Stereotactic Radiotherapy (FSRT)—based on optic nerve functional integrity and structural preservation to optimize long-term visual outcomes.

Materials/Methods: A retrospective single-institution analysis (2015–2023) included 9 patients (mean age: 46.8 ± 8.7 years; M:F = 5:4) with postoperative residual or recurrent ONS. All underwent baseline VEP (assessing P100 latency/amplitude) and OCT (retinal nerve fiber layer [RNFL] thickness) to evaluate conduction and structural integrity. Serial assessments were performed at 3-, 6-, and 12-months post-treatment, then annually for 5 years. MRI was conducted every 6–12 months for tumor control.

VEP and OCT Protocols:

    • P100 latency: A delay of 10–15 ms from baseline considered early optic nerve stress.

    • Amplitude: A drop >30% post-treatment suggested potential radiation-induced optic neuropathy (RON).

    • RNFL thickness: >100 µm = intact optic nerve; 70–100 µm = early axonal loss; <70 µm = significant optic atrophy.

Treatment Allocation:

    • FSRT (50 Gy/25 fractions, n=5): Patients with normal/mildly delayed VEP (P100 latency <130 ms, amplitude >70% baseline) and RNFL >100 µm.

    • SRS (12–14 Gy, n=4): Patients with severely delayed VEP (P100 latency >150 ms, amplitude <50%) or RNFL <70 µm/pre-existing optic neuropathy.

    • Intervention criteria: Progressive latency delay (>15 ms) or amplitude drop (>40%) triggered early intervention (steroid therapy and bevacizumab: 7.5 mg/kg IV biweekly × 3 cycles).

Outcomes:

    • Primary: Local control (tumor stability/regression on MRI).

    • Secondary: Visual preservation (VEP/OCT trends, visual acuity/fields).

Results:

  • Local Control: 100% tumor control at 5 years in FSRT group vs. 75% in SRS group (one patient had mild progression post-SRS).

  • Visual Function Outcomes:
    • FSRT: 80% (4/5) maintained stable VEP/vision; one had mild deterioration.
    • SRS: 50% (2/4) developed progressive optic neuropathy (latency +18.2 ± 6.4 ms, amplitude drop 42.3 ± 9.8%); 2 remained stable.

    • Overall 5-year VEP stability: 66.7% (6/9).

  • Radiation-Induced Optic Neuropathy (RON) Risk: 50% (2/4) in SRS group developed RON within 24 months vs. 0% in FSRT (p = 0.04).

Conclusion: VEP and OCT effectively guide therapeutic stratification for ONS. FSRT (50 Gy/25 fractions) demonstrates superior local control (100%) and visual preservation, favoring its use in patients with intact optic nerve function (P100 latency <130 ms, RNFL >100 µm). SRS (12–14 Gy) remains viable for high-risk cases with pre-existing neuropathy but carries a significant RON risk (50%). Integrating neurophysiological and structural metrics into decision-making enhances safety and functional outcomes, though larger cohorts are needed for validation.