Hemangioblastoma
- Hemangioblastoma is a benign, vascular tumor that loves the posterior fossa — classically the cerebellum, brainstem, or spinal cord.
- The signature look is a cyst with an enhancing mural nodule: a fluid-filled bubble with one small, intensely enhancing lump on its wall.
- That nodule sits right at the pial surface and often has flow voids — tiny black squiggles on MRI that betray its big feeding vessels.
- It's the most common primary intra-axial tumor in the adult posterior fossa.
- If you see one (or several) in a young adult, think von Hippel–Lindau and go hunting for the rest.
Imagine a water balloon with a single grape stuck to the inside of its wall. The balloon is mostly just fluid doing nothing interesting, but that one grape? That's the whole tumor. Everything that matters about a hemangioblastoma lives in that little nodule — the cyst is mostly innocent bystander fluid. Once you've seen the "cyst-plus-grape" pattern in the back of the head, you basically can't un-see it.
What it actually is
A hemangioblastoma is a benign tumor made of blood vessels — a tangled knot of capillaries with foamy fat-filled cells wedged between them. "Benign" here means it doesn't invade or spread; it just grows slowly and causes trouble by taking up space in a part of the brain that has zero room to spare. It's WHO grade 1, which is about as polite as brain tumors get.
It is, by a wide margin, the most common primary intra-axial (brain-substance) tumor in the adult posterior fossa. The runner-up in that neighborhood is usually a metastasis, which matters because the two can look almost identical — more on that headache below.
The classic picture
The textbook hemangioblastoma is a cyst with an enhancing mural nodule — "mural" just means on the wall. The cyst fluid follows the brain's cerebrospinal fluid closely on every sequence, and the cyst wall itself usually does not light up with contrast. The nodule does, and it does so dramatically.
Three things give the nodule away:
| Feature | What you see | Why it happens |
|---|---|---|
| Avid enhancement | The nodule glows after gadolinium contrast | It's basically a ball of leaky vessels |
| Pial location | Nodule abuts the surface of the cerebellum | These tumors hug the pia, where the blood supply is |
| Flow voids | Tiny black serpentine lines in/near the nodule on MRI | Fast-flowing blood in enlarged feeding arteries |
Those flow voids are the detail that turns a good guess into a confident one. They're the tumor showing off its plumbing.
Not every hemangioblastoma reads from the same script. Roughly a third are solid tumors with little or no cyst — just an enhancing, vascular mass. So "no cyst" does not let you off the hook, especially in the spinal cord, where the solid form is more common.
The company it keeps: von Hippel–Lindau
Most hemangioblastomas are sporadic and solitary — one tumor, no syndrome, usually middle-aged. But when you find them in a young adult, or you find more than one, alarm bells should ring for von Hippel–Lindau (VHL), an inherited syndrome covered with the neurocutaneous syndromes.
VHL is the gift that keeps on giving, and not in a good way. Multiple CNS hemangioblastomas (brain and spine), plus a grab-bag of other tumors elsewhere in the body.
When you call a hemangioblastoma in someone young, look at the whole neuraxis — image the spine too. In VHL these tumors come in clusters, and a single brain finding is often the tip of the iceberg. Mentioning VHL in your report can change the patient's entire workup.
The trap: it looks just like a met
Here's the headache I promised. A single solid enhancing posterior fossa mass in an adult could be a hemangioblastoma, or it could be a metastasis (lung, breast, kidney — the usual suspects). They can look maddeningly similar.
A cerebellar metastasis and a solid hemangioblastoma both enhance avidly and both love the posterior fossa. Clues that favor hemangioblastoma: a pial-based nodule, prominent flow voids, a cyst-plus-nodule shape, and youth or a VHL history. A known primary cancer and multiple lesions tilt you toward mets. When you genuinely can't tell, say so — and let the clinical picture break the tie.
One more wrinkle worth knowing: a minority of hemangioblastomas secrete erythropoietin, the hormone that tells the marrow to make red cells. When they do, the patient can end up with polycythemia (too many red blood cells). It's a neat physiologic footnote, and occasionally the clue that points back at the tumor.
The one thing to remember
If you take a single image away from this page, make it the water balloon with a grape on the wall, sitting in the back of an adult's head. Cyst with an enhancing mural nodule, flow voids, pial surface — and if there's more than one, you start spelling out von Hippel–Lindau. Everything else is detail hanging off that one bright little nodule.