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Kernohan’s Notch Sign – A Comprehensive Guide

What is Kernohan’s Notch Sign?

Kernohan’s Notch Sign (KNS) is a radiologic and clinical phenomenon that indicates severe midline shift of the brain, most often caused by a large intracranial mass or hemorrhage. When the brain is forced against the rigid skull base, the contralateral cerebral peduncle becomes compressed against the tentorial edge, creating a “notch” that appears on imaging studies (CT or MRI). Paradoxically, the patient may present with neurological deficits on the same side as the lesion, which can mislead clinicians if the sign is not recognized.

The sign is named after Dr. Daniel Kernohan, who described the finding in 1929 while studying traumatic brain injuries. Recognizing KNS is important because it signals a life‑threatening mass effect that often requires urgent neurosurgical intervention.

Sources: Mayo Clinic, Neurosurgery Textbook (Greenberg), Journal of Neuroimaging 2021.

Common Causes

Any intracranial process that creates a large, unilateral mass effect can produce Kernohan’s Notch Sign. The most frequently reported etiologies include:

• Acute epidural hematoma – rapid arterial bleeding between dura and skull.
• Acute subdural hematoma – venous bleed on the brain surface.
• Large intracerebral (intraparenchymal) hemorrhage – often hypertensive.
• Space‑occupying tumors – e.g., glioblastoma multiforme, meningioma.
• Brain abscess – localized infection with pus collection.
• Ischemic stroke with massive cerebral edema – especially malignant middle cerebral artery infarction.
• Subarachnoid hemorrhage with hydrocephalus – causing rapid ventricular enlargement.
• Cerebral venous sinus thrombosis – leading to venous congestion and edema.
• Traumatic brain injury (TBI) with severe brain swelling.
• Chiari malformation type I (rare) – downward herniation of cerebellar tonsils can produce similar notching.

Associated Symptoms

Because Kernohan’s Notch Sign reflects a massive shift of brain structures, patients often experience a constellation of neurologic deficits that develop rapidly. Commonly reported symptoms include:

• Contralateral hemiparesis that appears on the same side as the lesion (the classic “false‑localizing” sign).
• Altered level of consciousness – from drowsiness to coma.
• Headache – usually severe, sudden, and “worst of my life.”
• Nausea and vomiting – often non‑bloody.
• Pupillary changes – ipsilateral pupil dilation (due to oculomotor nerve compression).
• Seizures – especially with cortical irritation from bleed or tumor.
• Visual field deficits – homonymous hemianopia if occipital lobe is involved.
• Ataxia or dysmetria – when the cerebellar peduncle is affected.
• Speech difficulties – aphasia or dysarthria depending on dominant hemisphere.

When to See a Doctor

Kernohan’s Notch Sign itself is a radiologic finding, but the underlying conditions require immediate medical attention. Seek care promptly if you or someone else experiences:

• Sudden, severe head or facial pain with vomiting.
• Rapidly worsening weakness or numbness on one side of the body.
• New confusion, difficulty speaking, or loss of consciousness.
• Pupil that is markedly larger than the other or unresponsive to light.
• Any seizure that occurs without a known epilepsy diagnosis.
• Signs of increasing intracranial pressure (e.g., bulging fontanelle in infants).

These symptoms may represent the underlying cause of Kernohan’s Notch Sign and should prompt emergency evaluation.

Diagnosis

Diagnosis involves a combination of clinical assessment and neuro‑imaging studies.

1. Clinical Neurological Examination

• Assessment of motor strength, sensation, cranial nerve function, and level of consciousness.
• Documentation of any “false‑localizing” deficits (e.g., hemiparesis opposite the lesion).

2. Imaging

• CT Scan (non‑contrast) – First‑line in trauma or acute bleed; shows mass effect, midline shift, and the characteristic “notch” in the opposite cerebral peduncle.
• MRI (T1, T2, FLAIR, DWI) – Provides superior soft‑tissue detail, helpful for tumors, abscesses, or subtle edema.
• CT Angiography / MR Angiography – When vascular lesions (e.g., aneurysm, AVM) are suspected.

3. Ancillary Tests

• Complete blood count, coagulation profile, electrolytes – to assess bleed risk.
• Blood pressure monitoring – especially for hypertensive hemorrhage.
• Lumbar puncture – only after imaging rules out mass effect; useful for infection or subarachnoid bleed.

4. Neuro‑monitoring (in ICU)

In severe cases, intracranial pressure (ICP) monitors, transcranial Doppler, and continuous EEG may be employed to guide treatment.

Treatment Options

Treatment is directed at the underlying cause of the mass effect, while simultaneously controlling intracranial pressure and protecting brain tissue.

Medical Management

• Osmotherapy – Mannitol or hypertonic saline to reduce edema.
• Corticosteroids – Dexamethasone for vasogenic edema, especially in tumors.
• Antihypertensive therapy – Rapid BP control in hypertensive intracerebral hemorrhage (e.g., nicardipine infusion).
• Anticonvulsants – Levetiracetam for seizure prophylaxis in hemorrhage or tumor.
• Antibiotics/Antifungals – When an abscess is identified.
• Blood product administration – Reverse coagulopathy (vitamin K, PCC) if bleeding is due to anticoagulants.

Surgical Intervention

• Craniotomy or Burr‑hole evacuation – Preferred for acute epidural/subdural hematomas.
• Decompressive Craniectomy – Removes a large segment of skull to allow swollen brain to expand; indicated in malignant stroke or refractory ICP.
• Tumor resection – Microsurgical removal or stereotactic radiosurgery for selected neoplasms.
• Endoscopic drainage – For certain intraventricular hemorrhages or cystic lesions.

Rehabilitation and Home Care

• Early physical, occupational, and speech therapy to regain function.
• Fall‑prevention strategies and home modifications after discharge.
• Medication adherence and regular follow‑up imaging to monitor resolution of the notch.

Prevention Tips

Many causes of Kernohan’s Notch Sign are preventable or modifiable. Consider the following:

• Control blood pressure – Aim for <130/80 mmHg; adhere to antihypertensive regimen.
• Use protective headgear – When cycling, skiing, or engaging in contact sports.
• Avoid excessive alcohol and illicit drug use – Reduces risk of traumatic brain injury and hemorrhagic stroke.
• Manage anticoagulation carefully – Regular INR checks for warfarin; discuss DOAC dosing with your provider.
• Prompt treatment of infections – Dental, sinus, or skin infections can seed brain abscesses.
• Maintain healthy weight and cholesterol – Lowers risk of atherosclerotic disease and subsequent large strokes.
• Regular medical check‑ups – Early detection of tumors or vascular malformations.

Emergency Warning Signs

Bottom Line

Kernohan’s Notch Sign is a critical radiologic clue that a brain is being forced against the tentorial edge, indicating a severe, often life‑threatening mass effect. While the sign itself cannot be treated, rapid identification of the underlying cause—whether it is a bleed, tumor, infection, or massive stroke—allows clinicians to intervene promptly, often saving lives and preserving neurological function. Understanding the warning symptoms, seeking urgent medical care, and following preventive measures can dramatically improve outcomes.

For further reading, consult reputable sources such as the Mayo Clinic, the CDC, the NIH, and peer‑reviewed journals like Journal of Neuroimaging and Neurosurgery.

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