Sturge-Weber Syndrome (SWS)
Summary
Sturge-Weber Syndrome (SWS) is a rare neurocutaneous disorder characterized by the triad of a facial Port Wine Stain (PWS), Leptomeningeal Angiomatosis (brain blood vessel malformation), and Glaucoma. Unlike other Phakomatoses (NF1, TSC), SWS is NOT HEREDITARY. It is caused by a somatic mosaic mutation in the GNAQ gene. The defining feature is the PWS in the ophthalmic (V1) distribution of the trigeminal nerve. The brain lesion is ipsilateral to the skin lesion. It causes severe, intractable epilepsy (often starting in infancy), hemiparesis, and intellectual disability. Management involves pulsed-dye laser for the skin, aggressive antiepileptic therapy, and often epilepsy surgery (Hemispherectomy) for refractory cases. [1,2]
Key Facts
- Genetics: Somatic Mosaicism (Post-zygotic mutation) in GNAQ. It is sporadic.
- The Triad:
- Skin: Port Wine Stain (Naevus Flammeus) in V1.
- Brain: Leptomeningeal Angiomatosis (occipital/parietal).
- Eye: Glaucoma / Buphthalmos ("Ox eye").
- Tram-Track Calcium: The classic radiological sign. Calcification of the cortex underlying the angioma.
- Stroke-like Episodes: Transient hemiparesis often unrelated to seizure activity (vascular steal?).
- Hemispherectomy: SWS is the most common indication for this radical surgery in infancy, and it is curable for the epilepsy.
Clinical Pearls
"It must follow the Nerve": A port wine stain on the cheek or jaw (V2/V3) carries a LOW risk of brain involvement. Only a PWS involving the forehead/eyelid (V1) carries the high risk (25%).
"The Eye Check": Glaucoma is silent. Every baby with a V1 PWS must have intraocular pressure checked immediately.
"Tram Lines": The calcification is not in the blood vessel itself, but in the hypoxic cortex underneath it.
Incidence
- Frequency: 1 in 20,000 to 50,000.
- Inheritance: None (Sporadic).
The GNAQ Mutation
- Gene: GNAQ (G-protein subunit alpha q).
- Role: Regulates intracellular signaling pathways.
- Mutation: c.548G>A (p.Arg183Gln).
- Mechanism: The mutation activates the pathway constitutively, leading to malformation of capillaries.
- Why is it V1?: The mutation likely occurs in a progenitor cell that supplies the embryonic forehead, eye, and forebrain (shared developmental origin).
The "Steal" Phenomenon
- The leptomeningeal angioma is a venous malformation.
- It causes venous stasis and congestion.
- This leads to chronic ischaemia of the underlying cerebral cortex.
- Result: Atrophy, Calcification, and Seizures.
1. Dermatological (Port Wine Stain)
2. Neurological
3. Ophthalmological
Imaging (MRI Brain with Contrast)
The Gold Standard.
- Angioma: Enhancing leptomeningeal lesion (pial).
- Atrophy: Hemiatrophy of the affected hemisphere.
- Choroid Plexus: Enlarged ipsilaterally.
CT Head
- Calcification: "Tram-track" gyriform calcification (cortical). Better seen on CT than MRI.
EEG
- Asymmetry: Voltage depression over the affected hemisphere (due to atrophy/calcification).
- Epileptiform discharges.
Ophthalmology
- Tonometry (Pressure).
- Fundoscopy.
Management Algorithm
DIAGNOSIS (V1 Naevus)
↓
┌───────┬───────────┬──────────────┐
SKIN EYE BRAIN BRAIN
↓ ↓ ↓ ↓
Laser Drops/ Seizure Refractory?
(PDL) Surgery Meds ↓
SURGERY
(Hemispherectomy)
1. Dermatological
- Pulsed Dye Laser (PDL): Standard of care.
- Timing: Start early (infancy) for best results. Requires general anaesthetic in babies.
- Goal: Lightening of the stain. Prevention of hypertrophy.
2. Neurological (Medical)
- Antiepileptics:
- Carbamazepine / Oxcarbazepine (First line for focal seizures).
- Levetiracetam.
- Low Dose Aspirin: Controversial but widely used. Reduces thrombotic events in the sluggish angioma vessels? May prevent stroke-like episodes.
3. Neurological (Surgical)
- Hemispherectomy / Hemispherotomy:
- Indication: Drug-resistant epilepsy with hemiplegia.
- Procedure: Disconnecting the entire affected half of the brain.
- Outcome: Seizure freedom in >80%.
- The Trade-off: The child will have permanent hemianopia and hemiplegia (which they often have anyway), but cognition is preserved/improved.
4. Ophthalmological
- Latanoprost / Timolol drops.
- Trabeculectomy / Shunt surgery for glaucoma.
"Not in the Sperm, Not in the Egg."
- If you test the patient's blood leukocytes, the GNAQ mutation is usually ABSENT.
- Why? Because the mutation happened after the blood cell lineage separated from the skin/brain lineage.
- Testing: You must biopsy the affected skin (Port Bride Stain) to find the mutation.
- Implication: Siblings are at virtually NO risk. It is a random accident of development.
"Seizures masquerading as Stroke?"
- Children with SWS often present with sudden onset weakness (hemiparesis) lasting days.
- Mechanism: Is it a clot? Probably not always.
- It is often Post-Ictal Todd's Paresis prolonged by the underlying venous stasis.
- Vascular Steal: Seizures increase metabolic demand. The malformed vessels cannot supply blood. The cortex suffers relative ischaemia.
- Management: Aggressive seizure control is key.
"Half a Brain is better than a Broken One."
- Anatomy: The aim is to disconnect the Frontal, Parietal, Temporal, and Occipital lobes of one side from the rest of the nervous system.
- Technique: We do not remove the brain tissue (Anatomical Hemispherectomy) anymore due to complications (Haemosiderosis). We perform a Functional disconnection.
- Cut the Corpus Callosum (Callosotomy).
- Resect the Temporal Mesial structures.
- Disconnect the Frontal and Parietal opercula.
- Neuroplasticity: Because this is done in young children, the remaining healthy hemisphere takes over language and function remarkably well.
Selective Photothermolysis.
- Target: Oxyhaemoglobin (Red pigment).
- Wavelength: 585-595 nm (Yellow light).
- Pulse Duration: Short (0.45 - 40 ms). Matches the Thermal Relaxation Time of the capillaries.
- Effect: The laser energy is absorbed by the blood, heating it and destroying the vessel wall, without burning the overlying skin.
- Purpura: The distinct bruising seen after treatment (exploding capillaries).
- Epilepsy: The major determinant of Quality of Life. Early onset (under 2 years) predicts poorer cognitive outcome.
- Motor: Hemiparesis is common.
- Vision: Glaucoma can cause blindness if missed.
- Cosmetic: Laser is effective but rarely clears the stain completely.
What is Sturge-Weber Syndrome?
It is a condition caused by a tiny genetic "spelling mistake" in the skin and brain cells while the baby was growing in the womb. It causes a red birthmark on the face and epilepsy.
Is it inherited?
No. It is a random event. Your other children are not at risk.
Can we fix the birthmark?
We use laser treatment to fade it. It takes many sessions, usually starting in infancy.
Will my child have seizures?
Most likely, yes. We use strong medication to stop them. If the seizures are very bad, we sometimes consider surgery to disconnect the abnormal part of the brain.
- Comi AM. Sturge-Weber syndrome. Handb Clin Neurol. 2015.
- Bissler JJ, et al. Sturge-Weber Syndrome. Pediatrics. 2014.
Common Exam Questions
1. Radiology:
- Q: What is the classic CT sign?
- A: Tram-track cortical calcification.
2. Dermatology:
- Q: Which dermatome predicts brain involvement?
- A: The Ophthalmic (V1) dermatome.
3. Genetics:
- Q: What is the inheritance pattern?
- A: Sporadic (Somatic Mosaicism).
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