Stereotactic Navigation and Diagnostic Biopsy — WACS Viva & Clinical Scenarios (Functional Neurosurgery, Epilepsy, and Pain)

Exam-style stereotactic navigation and diagnostic biopsy viva scenarios with examiner probes and model answers for Neurosurgery candidates.

Scenarios covered

• SCENARIO 1: A 52-year-old male presents with progressive left hemiparesis and cognitive slowing. Magnetic resonance imaging demonstrates a heterogeneous, non-enhancing 3.5 cm mass centered in the right posterior thalamus abutting the posterior limb of the internal capsule. Discuss the indications, preoperative trajectory planning, mechanical frame application, and procedural execution for a frame-based stereotactic needle biopsy in this patient.
• SCENARIO 2: Written Short Answer Question: Define the mathematical principles underlying the Cartesian coordinate system in arc-centered stereotactic surgery. Differentiate between Target Registration Error (TRE), Fiducial Registration Error (FRE), and Fiducial Localization Error (FLE) in frameless optical neuronavigation, detailing the clinical and biomechanical factors that contribute to intraoperative brain shift.
• SCENARIO 3: Operative Technique and Troubleshooting Viva: Detail the step-by-step technique for performing a diagnostic brain biopsy of a deep-seated periventricular lesion using a side-cutting Sedan cannula. Explain how intraoperative squash preparation cytology influences procedural decision-making when the initial core specimen yields only necrotic debris or non-specific reactive astrogliosis.
• SCENARIO 4: Emergency Management and Critical Care Scenario: Two hours following an uncomplicated stereotactic biopsy of a deep basal ganglia lesion, the patient develops acute pupillary asymmetry, a drop in Glasgow Coma Scale score from 15 to 8, and dense contralateral hemiplegia. Outline the immediate diagnostic algorithm, emergency resuscitation protocol, and surgical decision tree for post-biopsy intracranial haemorrhage.
• SCENARIO 5: Comparative Instrumentation and Modality Question: Compare optical infrared tracking systems and electromagnetic neuronavigation systems in cranial surgery. Discuss their respective physical mechanisms, procedural limitations, susceptibility to line-of-sight obstruction or metallic interference, and methods for mitigating error during patient positioning.