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Awake craniotomy and intraoperative brain mapping
When a tumour lies near a language or motor area, direct electrical stimulation mapping while the patient is awake allows maximal removal without permanent deficit — because extent of resection in glioma improves survival, but a new neurological deficit cancels the benefit.
Why it matters in the exam
Awake surgery suits a tumour in the dominant hemisphere near Broca's and Wernicke's areas or the arcuate fasciculus, and sometimes near the motor cortex. Anaesthesia: an "asleep-awake-asleep" technique or monitored sedation; dexmedetomidine is useful because it calms without depressing breathing. During mapping the cortex is stimulated with a bipolar probe and the patient is asked to count and name pictures: speech arrest or naming errors mark an area that must not be removed. A seizure triggered by stimulation is stopped by irrigating the cortex with cold fluid. Contraindications: severe aphasia that prevents testing, lack of cooperation, severe anxiety and significant obstructive sleep apnoea.
In the motor area motor evoked potential (MEP) monitoring is used: a sustained fall of more than 50% in amplitude is a warning sign. The central sulcus is identified by "phase reversal" of the somatosensory evoked potential (SSEP) over the cortex. In high-grade glioma, 5-ALA fluorescence-guided resection raised the rate of complete removal of the enhancing part to 65% versus 36% under white light and improved six-month progression-free survival. Other tools: navigation, intraoperative MRI and ultrasound. Common exam questions on this subject, which recur almost every year: "which finding predicts deficit" (MEP fall), "what to do for an intraoperative seizure" (cold irrigation), and "who is unsuitable for awake surgery".
Key points
- Awake surgery — tumour near language areas in the dominant hemisphere.
- Speech arrest — do not resect.
- MEP: fall of more than 50% — warning.
- SSEP phase reversal identifies the central sulcus.
- 5-ALA: complete removal 65% versus 36%.
Summary table
| Tool | What it identifies | Warning sign or finding | Action |
|---|---|---|---|
| Direct cortical stimulation awake | Language areas | Speech arrest, naming errors | Do not resect the area |
| MEP | Integrity of the motor pathway | Fall of more than 50% | Stop and change technique |
| SSEP phase reversal | The central sulcus | Reversal of the wave between electrodes | Mark the motor area |
| 5-ALA | High-grade glioma tissue | Red fluorescence | Complete removal of the enhancing part 65% versus 36% |
| Cold irrigation | Stimulation-induced seizure | Seizure stops | Continue mapping |
A free exam question
במטופל עם חשד קליני גבוה לווסקוליטיס בנוכחות בדיקת DSA )אנגיוגרפיה( שלילית, בוצעה ביופסיית מוח וקרומים שהדגימה דפוס דלקת לימפוציטי. הוחלט על טיפול משולב של סטרואידים ו- Cyclophosphamide . איזה מהסיבוכים הבאים מחייב ניטור קפדני תחת טיפול ב- Cyclophosphamide ? (the question as examined, in Hebrew)
- א. Hypercalcemia
- ב. Hemorrhagic cystitis
- ג. Pulmonary hypertension
- ד. התפתחות Type 1 diabetes
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Sources
- EANO guideline on the diagnosis and treatment of diffuse gliomas of adulthood, 2021 — Extent of resection and intraoperative techniques
- Stummer et al., 5-ALA fluorescence-guided resection of malignant glioma (Lancet Oncology), 2006 — Complete resection rates
- International Society of Intraoperative Neurophysiology recommendations, 2013 — Motor evoked potentials and cortical mapping
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.