What is Phakomatoses?

The phakomatoses for clinical practice: NF1, NF2, tuberous sclerosis, Sturge-Weber, and von Hippel-Lindau, with the skin plus tumor clue for each in an interactive grid.

Why does Phakomatoses matter for clinical practice?

Phakomatoses is a high-yield board topic; this deep dive walks the pathophysiology, presentation, diagnosis, and management with original clinical vignettes.

Why does Phakomatoses matter for clinical practice?

Phakomatoses is a high-yield board topic; this deep dive walks the pathophysiology, presentation, diagnosis, and management with original clinical vignettes.

Phakomatoses: Neurocutaneous Syndromes Compared (Medical Education)

Step 1 · The Big Picture

All five phakomatoses, side-by-side

Each row is a discriminator. Scan the columns and the patterns jump out: TSC = tumors everywhere, Sturge-Weber = vascular face + brain, VHL = vascular cerebellum + kidney. NF1/NF2 abbreviated here · tap the chip in the hero for the full page.

	Tuberous Sclerosis	Sturge-Weber	VHL	NF1 ›	NF2 ›
Phakomatoses comparison
Inheritance	Autosomal dominant	Sporadic (somatic mosaic)	Autosomal dominant	Autosomal dominant	Autosomal dominant
Chromosome	9 (TSC1) or 16 (TSC2)	Mosaic, not inherited	3p25	17	22
Gene / protein	Hamartin / tuberin (mTOR brake)	GNAQ somatic mutation	VHL tumor suppressor (tags HIF-1α)	Neurofibromin (Ras brake)	Merlin (membrane organizer)
Brain finding	Cortical tubers, subependymal nodules, SEGA at foramen of Monro · seizures + intellectual disability	Leptomeningeal angioma, tram-track calcifications · seizures + intellectual disability	CNS hemangioblastoma (cerebellum, brainstem, spinal cord)	Optic pathway glioma (often pilocytic astrocytoma)	Bilateral vestibular schwannomas, meningiomas
Skin finding	Ash-leaf spots, shagreen patch, facial angiofibromas (adenoma sebaceum)	Port-wine stain in trigeminal V1 distribution · present at birth	Rare cutaneous angiomatosis	Cafe-au-lait spots, axillary freckling, neurofibromas, Lisch nodules	None typical (NF2 has no skin signature)
Other organ	Cardiac rhabdomyoma, renal angiomyolipoma	Choroid angioma → glaucoma, vision loss	Clear-cell RCC, pheochromocytoma, pancreatic + epididymal cysts, retinal hemangioblastoma	Pheochromocytoma (less common than VHL), scoliosis, learning disability	Cataracts (juvenile), ependymomas

Step 2 · Tap a Syndrome

Open the case

Each card is a stem-style cluster of clues. Tap to expand into mnemonic, organ-by-organ findings, and the board trap.

Tuberous Sclerosis

Tumors Everywhere

TSC1 / TSC2 · mTOR loses its brake

Clue cluster: infant with seizures, ash-leaf spots on the back under Wood lamp, and a heart mass found on prenatal ultrasound that regresses by age 4.

See the case▾

Mnemonic "Tumors everywhere" · brain (tubers + SEGA), heart (rhabdomyoma), kidney (angiomyolipoma), skin (ash-leaf + shagreen + angiofibroma). Classic triad: seizures + intellectual disability + facial angiofibromas.

Brain

Cortical tubers and subependymal nodules cause seizures (often infantile spasms) and intellectual disability. SEGA (subependymal giant-cell astrocytoma) parks at the foramen of Monro and can block CSF → hydrocephalus.

Heart

Rhabdomyoma · benign muscle tumor often found on prenatal ultrasound; the only phakomatosis with a cardiac tumor. Usually regresses spontaneously.

Kidney

Angiomyolipoma (AML) · fat + vessel + muscle. Bleeds catastrophically when large → surveillance imaging is the move.

Skin

Ash-leaf spots (hypopigmented macules, light up under Wood lamp) · shagreen patch (leathery LS lumbar plaque) · facial angiofibromas (adenoma sebaceum: red papules across nose + cheeks, post-puberty).

Treatment angle

mTOR inhibitors (everolimus, sirolimus) shrink SEGAs and AMLs · the disease IS uncontrolled mTOR, so the drug class is the mnemonic.

Sturge-Weber

The Vascular Web

Encephalotrigeminal angiomatosis · somatic GNAQ

Clue cluster: newborn with a port-wine stain across the forehead and upper eyelid, develops seizures at 4 months, and the eye on the same side has elevated intraocular pressure.

See the case▾

Mnemonic Sturge-WEBer · everything is a vascular web. Skin web (port-wine), brain web (leptomeningeal angioma), eye web (choroid angioma).

Brain

Leptomeningeal angioma over the same side as the port-wine stain → seizures + intellectual disability + hemiparesis on the opposite side. Imaging: "tram-track" gyriform calcifications from cortical atrophy under the angioma.

Eye

Choroid angioma on the affected side → glaucoma (high pressure) and progressive vision loss. Check eye pressure at birth in any baby with an upper-face port-wine stain.

Skin

Port-wine stain (nevus flammeus) · unilateral, deep red-violet, present at birth, in the trigeminal V1 (ophthalmic) dermatome. V1 involvement is the high-risk piece · V2 alone is rarely Sturge-Weber.

Inheritance

Sporadic · a somatic mosaic mutation in GNAQ in early embryo. Not inherited, not passed down. The only phakomatosis here that is not autosomal dominant.

Board trap

Not every port-wine stain is Sturge-Weber. The brain + eye findings require the stain to be in V1. A port-wine stain on the leg = isolated capillary malformation, not Sturge-Weber.

Von Hippel-Lindau

The Vascular Hunger

VHL tumor suppressor on 3p25

Clue cluster: a 35-year-old presents with cerebellar ataxia, headaches, and on workup has a cystic cerebellar mass, blood in the urine, and an episodic headache + palpitation + sweating crisis.

See the case▾

Mnemonic VHL = "Very Hungry Lungs of capillaries" · lose the VHL brake, HIF-1α piles up, growth signals scream build vessels. Hemangioblastomas, RCC, pheo · every lesion is fed by overgrown vasculature.

Brain & spine

CNS hemangioblastomas · cerebellum (classic), brainstem, spinal cord. Cystic mass + mural nodule + cerebellar ataxia. Can secrete EPO → secondary polycythemia.

Eye

Retinal hemangioblastoma (capillary hemangioma) · same tumor in the retina. Early dilated funduscopy can catch VHL before brain symptoms appear.

Kidney

Clear-cell renal cell carcinoma (often bilateral, often multifocal) and multiple renal cysts. Leading cause of death in VHL.

Adrenal

Pheochromocytoma · episodic hypertension, headache, palpitations, diaphoresis. Always rule out before any surgery in a VHL patient.

Other

Pancreatic cysts and neuroendocrine tumors, epididymal cystadenomas, endolymphatic sac tumors (causing hearing loss).

Step 3 · The Body Map

"Tumors everywhere" · tap an organ

TSC drops a hamartoma in every system. Tap a glowing zone on the silhouette to see the finding and the board pearl.

Tap a glowing zone to read the lesion.
TSC drops a hamartoma in every system · that is the whole shape of the disease.

Brain

Glial hamartomas, cortical tubers, SEGA

Subependymal nodules and cortical tubers cause seizures (often infantile spasms) and intellectual disability. SEGA (subependymal giant-cell astrocytoma) sits at the foramen of Monro and can obstruct CSF.

Pearl: SEGA at the foramen of Monro is the TSC brain tumor everyone gets quizzed on. New-onset hydrocephalus in a TSC patient = SEGA blocking the foramen.

Heart

Rhabdomyoma

Benign muscle tumor often picked up on prenatal ultrasound. Frequently regresses on its own by age 4. Can cause arrhythmias or outflow obstruction in infancy.

Pearl: Cardiac rhabdomyoma in a fetus or infant → check for TSC. It is the only phakomatosis with a cardiac tumor.

Kidney

Angiomyolipoma (AML)

Fat + vessels + smooth muscle. Often bilateral. Big AMLs bleed catastrophically (Wunderlich hemorrhage). Renal cysts may also be present.

Pearl: Painless flank mass or hematuria in a young TSC patient → image the kidneys. AML > 4 cm = consider embolization or mTOR inhibitor.

Skin

Ash-leaf spots · shagreen · angiofibromas

Ash-leaf spots: hypopigmented macules, brightest under Wood lamp. Shagreen patch: leathery raised plaque, usually lumbar. Facial angiofibromas (adenoma sebaceum): red papules across nose + cheeks, post-puberty.

Pearl: A baby with infantile spasms? Get a Wood lamp. Ash-leaf spots are often the first visible sign of TSC.

Step 4 · The V1 Rule

Port-wine stain plus V1 = think Sturge-Weber

A port-wine stain anywhere on the body is a capillary malformation. The one that drags brain and eye into the picture is the one that sits in the trigeminal V1 (ophthalmic) branch.

The Rule

Port-wine stain in V1 (ophthalmic) → suspect Sturge-Weber · image the brain, check eye pressure.

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V1 (forehead, upper eyelid, scalp). The branch that shares vascular territory with the leptomeninges and eye. This is the high-risk zone.
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V2 (cheek, upper lip). Lower risk, mostly cosmetic.
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V3 (lower lip, jaw). Lower risk again.
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Bilateral V1 involvement → even higher seizure and developmental risk.
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Workup: MRI with contrast (look for leptomeningeal enhancement and tram-track calcifications), ophthalmology referral, EEG if seizures.

Step 5 · The VHL Engine

Why VHL grows vessels · tap the switch

VHL is a tumor suppressor whose only job is to tag HIF-1α for the shredder. Lose VHL, HIF-1α piles up, and the cell screams build more vessels. Every VHL tumor · hemangioblastoma, RCC, pheo, retinal hemangioma · is downstream of this one switch.

Oxygen sensedcell knows the state of perfusion

→

VHL proteinworking: tags HIF-1α

→

HIF-1αdegraded by proteasome

↓

VEGF / PDGF / EPOgrowth signals: low

→

Vessels stableno abnormal growth

→

No tumorscerebellum, retina, kidney quiet

Normal: When oxygen is adequate, VHL tags HIF-1α for degradation. Growth signals stay low. Vessels stay calm. No tumor.