Sturge-Weber Syndrome (SWS)

Epidemiology & Genetics

• Incidence: approximately 1 in 20,000 births
• Occurs sporadically in all races; no hereditary pattern
• Caused by a somatic (post-zygotic mosaic) activating mutation in GNAQ (chromosome 9q21.2), which encodes the alpha subunit of a heterotrimeric G-protein. The mutation reduces GTPase activity, increasing downstream cell signaling. Mutations in GNA11 have also been implicated.
• The mutation is not detectable on blood-based genetic testing (mosaic), so diagnosis relies on clinical and imaging findings.
• Pathogenesis: persistence of the primitive embryonal vascular plexus that normally regresses during the 9th fetal week (it develops in the 6th week around the cephalic neural tube and facial skin region).

Clinical Features (The Classic Triad)

1. Port-Wine Stain (Cutaneous Angioma)

Fig. Two patients with the classic port-wine nevus distribution - (A) adult with nodular texture development, (B) child with episcleral/conjunctival angioma on the affected side. (Bradley & Daroff's Neurology in Clinical Practice)

Fig. Bilateral facial port-wine stain (capillary malformation) in a patient with Sturge-Weber syndrome. (Andrews' Diseases of the Skin)

• Involves the forehead and upper eyelid (V1 trigeminal distribution); may extend bilaterally or to trunk/limbs
• Usually obvious at birth; may thicken and develop nodular texture over time
• Reactive hypertrophy of adjacent bone and soft tissue may occur
• Only 10%-20% of children with an upper facial port-wine nevus have a leptomeningeal angioma
• Risk is higher when the forehead is involved + larger area of face covered (especially bilateral V1 or V1/V2/V3)
• A port-wine stain sparing the upper face rarely associates with intracranial angioma

2. Leptomeningeal Angioma (Neurological Features)

• Primarily parieto-occipital distribution, typically ipsilateral to the facial nevus
• Bilateral in at least 15% of patients (including some with unilateral facial nevus)
• The angioma causes abnormal venous drainage → chronic ischemia → cortical atrophy + calcification

• Seizure onset before age 2 years strongly predicts future intellectual disability and refractory epilepsy
• Children who never develop seizures usually maintain normal intelligence
• The condition tends to stabilize, leaving residual deficits without further deterioration

3. Ocular Features

• Glaucoma - the principal ocular complication; two age peaks: infancy and late childhood
• Buphthalmos (enlarged globe) - in some newborns
• Choroidal hemangioma - ipsilateral diffuse choroidal angioma
• Episcleral hemangioma
• Iris heterochromia - ipsilateral to the nevus
• Amblyopia, retinal detachment, progressive blindness if untreated
• Blood in the Schlemm canal on gonioscopy is a recognized sign
• Glaucoma can occur even in the absence of neurologic involvement

Classification (Roach Scale)

Imaging

MRI (modality of choice)

Fig. Sturge-Weber Syndrome MRI: (A) Coronal T1 post-contrast - enhancing pial angioma over right hemisphere with atrophy + enlarged choroid plexus; (B) Axial T2 - prominent superficial and ependymal veins (arrows); (C) Axial post-contrast T1 - bilateral choroidal angiomas (arrows). (Grainger & Allison's Diagnostic Radiology)

• Gadolinium-enhanced MRI: gold standard - shows diffuse pial enhancement of variable thickness (leptomeningeal angioma), ipsilateral hemispheric atrophy, enlarged choroid plexus, dilated transparenchymal veins
• In infants <2 years, the brain may look normal even on contrast MRI
• "Burnt out" cases: pial angioma no longer enhances; only chronically shrunken calcified hemisphere remains
• Polymicrogyria may be seen

CT

• Shows cortical calcification earlier than plain X-ray
• Classic "tram-track" (trolley-track) calcification in outer cortical layers - rare in neonates, develops by age 2
• T2* sequences / SWI on MRI also detect calcification

Other

• PET: reduced cortical metabolism near the angioma (increased in recent-onset seizures)
• SPECT: reduced perfusion; often shows abnormality beyond the CT/MRI extent
• Cerebral angiography: no longer routine; shows abnormal veins > arteries; sparse superficial cortical veins with enlarged deep medullary veins

Diagnosis

1. Port-wine stain (upper face/periorbital)
2. Neuroimaging findings (leptomeningeal angioma, cortical atrophy, calcification)
3. Characteristic neurological and ophthalmological features

Management

Seizures (Epilepsy)

• Antiepileptic drugs (AEDs) - first-line; generally the more extensive the lesion, the harder to control
• Surgical resection (lobectomy or hemispherectomy) - for refractory epilepsy; can improve seizure control and intellectual development. Patient selection: refractory seizures + clinical dysfunction of the area + failure of adequate AED trial
• Corpus callosotomy - for refractory tonic/atonic seizures with extensive disease
• Patients with less extensive lesions: limited resection preferred to preserve normal brain

Prophylaxis

• Low-dose aspirin - offered to reduce stroke-like episodes, seizures, and cognitive impairment; generally well-tolerated, but efficacy not firmly established by RCTs. Early imaging is now recommended so aspirin can be started early in confirmed cases.

Ophthalmological

• Screening for glaucoma must begin in infancy
• Periodic intraocular pressure measurement is mandatory when the nevus is near the eye
• Surgical management of glaucoma as needed

Skin (Port-Wine Stain)

• Pulsed-dye laser therapy - effective for decreasing skin discoloration; most effective when started early
• Topical preparations (imiquimod, rapamycin) alone or with adjuvant laser show promise
• Soft tissue debulking in severe cases

Recent Evidence

• Cannabidiol treatment for SWS-related epilepsy - 2024 review (PMID: 39598668) covers molecular pathways and CBD data
• Overview of history, genetics, and management (2024) - Ramirez & Julich, Seminars in Pediatric Neurology (PMID: 39389653)
• Systematic review of headache in SWS - 2024, Cephalalgia (PMID: 39043228) - headache is an under-recognized feature
• Biomarker development - 2025 review on emerging biomarkers (PMID: 40851064)

Summary Table

Pathology of Sturge-Weber Syndrome

1. Molecular Pathogenesis

• Encodes the alpha subunit of a heterotrimeric G-protein (Gq class)
• Acts as a molecular switch - transmits signals from G protein-coupled receptors to downstream effectors
• Has intrinsic GTPase activity that "turns itself off"

• Most common substitution is at the R183 residue
• Reduces GTPase activity → the G-protein remains constitutively "stuck ON"
• Results in persistent activation of MAPK (mitogen-activated protein kinase) signaling → increased cell proliferation, decreased apoptosis
• Also activates ERK (extracellular signal-regulated kinase)

• A germline GNAQ mutation would be lethal; the mutation survives only because it occurs after fertilization in a subset of cells
• The mutation is present only in affected tissues (skin, meningeal endothelium) - NOT detectable in blood

• GNA11 (related G-protein α subunit) - also implicated in SWS and in blue nevi, nevus of Ota, uveal melanoma
• RASA1 and EPHB4 mutations - cause capillary malformation-AVM syndrome (different disease)
• Facial CM is thought to arise from clonal expansion of abnormal cells originating from the neural crest

2. Developmental / Embryological Basis

• During the 6th fetal week, a primitive vascular plexus forms around the cephalic neural tube and the region destined to become facial skin
• Normally, this plexus regresses during the 9th fetal week
• In SWS, the GNAQ mutation leads to failure of regression of this plexus
• There is a close anatomical correlation between the embryonic vascular plexus of the eyelid/forehead and that of the occipitoparietal brain - which explains why upper eyelid involvement predicts intracranial lesions

3. Gross / Macroscopic Pathology

Skin - Port-Wine Stain (Capillary Malformation)

• A vascular birthmark composed of a permanent collection of dilated postcapillary venules in the dermis
• Present at birth as a flat, pink-to-red lesion
• With age: darkens, thickens, develops a cobblestoned surface (two-thirds of affected adults)
• May develop nodular elevations and pyogenic granulomas
• Reactive hypertrophy of adjacent connective tissue and bone can produce facial asymmetry and skeletal deformity (resembling Klippel-Trenaunay-Weber)
• The port-wine stain is not a true neoplasm - it is a vascular ectasia (permanent dilation of preexisting small vessels)

Brain - Leptomeningeal Angioma

• Ipsilateral venous angioma of the cortical leptomeninges, predominantly parieto-occipital
• The angioma consists largely of abnormal veins, not arteries - easily distinguished from true AVM
• Overlying leptomeninges show diffuse vascular engorgement with tortuous, thin-walled venous channels
• The underlying cerebral cortex is progressively destroyed: it is replaced by glial tissue that subsequently calcifies
• Enlarged choroid plexus on the ipsilateral side
• Cortical atrophy (hemiatrophy in advanced cases) - progressive and ipsilateral
• In "burnt out" cases: only a chronically shrunken, calcified hemisphere remains with no enhancing angioma

Calcification - the Hallmark

• Calcium is deposited in the 2nd and 3rd layers of the cerebral cortex (Wohlwill and Yakovlev's classic finding - established by Krabbe who corrected the earlier belief that it was in blood vessels)
• The calcification follows the gyral convolutions of the parietooccipital cortex
• Produces the classic "tram-track" (double-contoured, tramline) pattern on plain X-ray and CT

4. Microscopic (Histological) Pathology

Port-Wine Stain (Skin)

• Dilated postcapillary venules within the papillary and upper reticular dermis
• Also areas of increased number of normal-looking capillaries
• Endothelial cells are flat (not proliferating - distinguishing it from a true hemangioma)
• Factor VIII, fibronectin, and basement membrane proteins are normal
• S100 staining shows abnormal innervation - reduced sympathetic innervation of the papillary vascular plexus
• The vessel ectasia (progressive widening without proliferation) is believed to result from abnormal neural (sympathetic) modulation of the papillary plexus
• Waner Classification (grades I-IV) correlates degree of vessel ectasia with degree of sympathetic denervation

Leptomeningeal Angioma (Brain)

• Thin-walled venous channels in the leptomeninges
• Sparse superficial cortical veins with enlarged, tortuous subependymal and medullary veins acting as collaterals
• Cortex below the angioma shows: neuronal loss, gliosis, and intracortical calcification in layers II and III
• Microscopic hemorrhages may be present (though significant intracranial hemorrhage is rare)
• Evidence of chronic ischemia: the leptomeningeal angioma "steals" blood from the cortex, leading to progressive neuronal loss
• Polymicrogyria is occasionally seen in SWS

5. Pathophysiological Cascade (How the Lesion Progresses)

GNAQ somatic mutation
        ↓
Failure of regression of embryonal vascular plexus
        ↓
Leptomeningeal venous angioma (abnormal draining veins)
        ↓
Impaired cortical venous drainage → chronic venous hypertension
        ↓
Chronic cortical ischemia + hypoxia
        ↓
Neuronal loss → Gliosis → Cortical atrophy
        ↓
Calcium deposition in layers II and III of cortex
        ↓
Epilepsy → further ischemia (vascular "steal" during seizures)
        ↓
Progressive hemiparesis, hemianopia, intellectual disability

1. Vascular steal: blood is diverted to the meninges during seizures → progressive ischemia of the cerebral cortex beneath
2. Seizures themselves are responsible for progressive deficits independent of ischemia

6. Ocular Pathology

• Glaucoma: episcleral vascular malformation increases episcleral venous pressure → impairs aqueous humor outflow through Schlemm's canal → raised IOP. Blood in the Schlemm canal on gonioscopy is a characteristic finding
• Buphthalmos: infantile glaucoma causes ocular enlargement before closure of growth plates in the sclera
• Choroidal hemangioma: diffuse, flat, orange-red choroidal hemangioma (capillary-venous malformation) - can cause exudative retinal detachment and vision loss

Imaging Correlation of Pathology

Fig. Left: Non-contrast CT showing calcification of the right parietal vascular malformation and underlying cortical atrophy. Right: T2-FLAIR MRI showing pronounced hemispheric atrophy in the same patient. (Adams & Victor's Principles of Neurology)