Neurocutaneous Syndromes (NF1/2, TS, VHL, SWS)
- Neurocutaneous syndromes ("phakomatoses") are inherited conditions where the same bad gene shows up in both the skin and the nervous system — so a skin clue often predicts a brain finding.
- NF1 = neurofibromas, optic pathway gliomas, and bright spots on T2 ("FASI"). NF2 = schwannomas (especially bilateral vestibular), meningiomas, and ependymomas — remember it as "MISME."
- Tuberous sclerosis scatters tubers, subependymal nodules, and the one tumor that can block CSF — the SEGA at the foramen of Monro.
- Von Hippel-Lindau grows hemangioblastomas (brain, cord, retina) plus tumors all over the body — kidneys, adrenals, pancreas.
- Sturge-Weber is the odd one out: not inherited, a facial port-wine stain with leptomeningeal vessels and "tram-track" cortical calcification underneath.
Here's a genuinely useful shortcut in radiology: sometimes the diagnosis is written on the patient's face. The neurocutaneous syndromes — the radiologists like the fancier word phakomatoses, which mostly just makes them sound smart at conferences — are conditions where one inherited glitch decides to decorate both the skin and the nervous system at the same time. Same gene, two billboards. Spot the skin finding, and you can often predict what the MRI is about to show you before you scroll.
Let me walk you through the big five, because they love to show up on exams and, more importantly, in real life.
NF1: the freckly one with the bright spots
Neurofibromatosis type 1 (NF1) is the common one. Think café-au-lait spots (flat tan patches, the color of coffee with too much milk), axillary freckling, and neurofibromas — soft nerve-sheath tumors that can stud the body like a beanbag chair that's seen better days.
On brain MRI, the classic finding is FASI — foci of abnormal signal intensity, also affectionately called "UBOs," unidentified bright objects. These are bright on T2/FLAIR, scattered in the basal ganglia, brainstem, and cerebellum, and here's the kind part: they usually don't enhance, don't cause mass effect, and tend to fade as kids grow up. They're a feature, not an emergency.
The one you can't shrug off is the optic pathway glioma — a low-grade tumor that thickens and buckles the optic nerves or chiasm. In NF1 it's the tumor that actually threatens vision, so the optic pathway gets a careful look every time.
A handy way to keep the two NFs straight: NF1 is peripheral and pigmented (skin, peripheral nerves, optic gliomas), while NF2 is central and tumor-heavy (cranial nerves and meninges). They are completely different genes on different chromosomes — not "mild vs. severe" versions of each other.
NF2: the schwannoma factory
NF2 skips most of the skin drama and goes straight for tumors lining the nervous system. The memory hook is MISME — Multiple Inherited Schwannomas, Meningiomas, and Ependymomas.
The signature is the bilateral vestibular schwannoma — a tumor on each eighth cranial nerve, sitting in the internal auditory canals like two ice-cream cones pointed at the brainstem. Bilateral vestibular schwannomas in a young person are essentially NF2 until proven otherwise. Stack on multiple meningiomas and spinal ependymomas, and the picture is complete.
A single vestibular schwannoma in an older adult is common and usually sporadic — not NF2. It's the bilateral ones, or a young patient with multiple schwannomas/meningiomas, that should make you reach for the NF2 diagnosis.
Tuberous sclerosis: tubers, nodules, and the gatekeeper tumor
Tuberous sclerosis complex (TSC) is the one that loves the word "tuber." Picture potatoes scattered through the cortex.
There are three brain findings worth memorizing, and they live in a tidy progression from the ventricle outward:
| Finding | Where | The catch |
|---|---|---|
| Cortical/subcortical tubers | Cortex | Often the seizure source; can calcify over time. |
| Subependymal nodules | Lining the ventricles | Bumpy "candle-drippings"; commonly calcify. |
| SEGA | At the foramen of Monro | The one that grows and blocks CSF flow. |
That last one — the subependymal giant cell astrocytoma (SEGA) — is the troublemaker. It sits right at the foramen of Monro, the narrow doorway CSF squeezes through, so when it enlarges and enhances, it can dam up the system and cause obstructive hydrocephalus. A subependymal nodule that grows and lights up with contrast over time is the tell.
Because seizures are central to TSC, this is also a frequent flier in epilepsy imaging.
Von Hippel-Lindau: the hemangioblastoma tour
Von Hippel-Lindau (VHL) is the body-wide one. Its calling card is the hemangioblastoma — a vascular tumor that classically looks like a cyst with an enhancing mural nodule, like a water balloon with a single bright pebble stuck to its wall. They love the cerebellum and spinal cord, and in VHL they show up in multiples and in retinas.
But VHL doesn't stay above the neck. It's a multi-organ affair: clear cell renal cell carcinomas and renal cysts, pheochromocytomas in the adrenals, and pancreatic cysts and tumors. So when you see a young person with a cerebellar hemangioblastoma, the radiologist's reflex is to wonder what the kidneys and adrenals are doing.
The phrase that should fire when you see a posterior-fossa "cyst with a mural nodule" in a young adult is hemangioblastoma → check for VHL → look at the whole body. One brain finding can reroute the entire workup.
Sturge-Weber: the one that isn't inherited
Sturge-Weber syndrome (SWS) is the rebel of the group — it's a sporadic vascular malformation, not a heritable gene you pass down. The skin clue is a port-wine stain on the face, typically in the distribution of the first trigeminal nerve branch (think forehead and upper eyelid).
Underneath that, abnormal leptomeningeal vessels drape over the brain on the same side, and the cortex beneath them slowly suffers. Over time the affected cortex atrophies and lays down calcification in a wavy, parallel pattern the textbooks call "tram-track" calcification — two thin curved lines following the gyri, like rails on a track.
The one-line takeaway
If you remember nothing else: the skin tells on the brain. A café-au-lait kid, a port-wine face, or a relative with bilateral hearing loss is a free hint about what the scan is going to show — and in this corner of radiology, free hints are worth grabbing.