[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Blood vessels](https://durgical.com/en/general-pathology/areas/vessels/) › Vascular anomalies: berry aneurysm, AV fistula, fibromuscular dysplasia

# Vascular anomalies: berry aneurysm, AV fistula, fibromuscular dysplasia

- Lesion

Some vessels are built wrong from the start: thin spots in brain arteries, direct artery-to-vein shortcuts, and arteries with lumpy muscular walls.

Updated Nov 12, 2026

## Key points

- Berry aneurysm: branch points of the anterior circle of Willis; rupture gives subarachnoid hemorrhage (‘worst headache of my life’).
- Associations of berry aneurysms: autosomal dominant polycystic kidney disease, Ehlers–Danlos type IV, hypertension and smoking.
- Arteriovenous fistula: congenital, traumatic or surgical (dialysis access); a large one can cause high-output heart failure.
- Fibromuscular dysplasia: ‘string of beads’ on angiography; a cause of renovascular hypertension in young women.

## What it is

Developmental anomalies of vessels are uncommon but cause dramatic disease. Berry (saccular) aneurysms form at branch points of the circle of Willis where the media is weak and can rupture into the subarachnoid space. Arteriovenous fistulas or malformations connect arteries directly to veins without capillaries. Fibromuscular dysplasia is a non-inflammatory, non-atherosclerotic thickening of the wall of medium arteries, classically the renal and carotid arteries of young women.

## Structure

- Berry aneurysm: thin-walled sac at an arterial fork; the media and internal elastic lamina stop at the neck; the dome is only intima and adventitia.
- Arteriovenous malformation: a tangle of thick and thin vessels with no capillary bed between them.
- Fibromuscular dysplasia: segments of irregular medial or intimal thickening alternating with thinned, dilated segments.

## Three developmental vascular anomalies compared

| Anomaly | Typical site | What the wall shows | What it leads to |
| --- | --- | --- | --- |
| [Berry (saccular) aneurysm](https://durgical.com/en/conditions/subarachnoid-haemorrhage/) | Circle of Willis branch points | Media missing at the neck; thin sac | Subarachnoid hemorrhage |
| [Arteriovenous fistula or malformation](https://durgical.com/en/conditions/brain-arteriovenous-malformation/) | Brain, lung, limbs, any organ | Direct artery-to-vein channels without capillaries | Bleeding, steal, high-output heart failure |
| [Fibromuscular dysplasia](https://durgical.com/en/conditions/renovascular-hypertension/) | Renal and carotid arteries | Fibrous or muscular ridges alternating with thin segments | Renovascular hypertension, dissection, stroke |

## Clinical notes

- Most berry aneurysms stay silent until they rupture; size and site predict the risk.
- In a young woman with resistant hypertension, fibromuscular dysplasia of the renal artery is a classic cause.

## Memory aid

A fork with no muscle (berry), a road with no town in between (fistula), and a road paved in beads (fibromuscular dysplasia).

## Test yourself

Think of the answer, then tap the question to see it.

## Which kidney disease is classically associated with berry aneurysms?

Autosomal dominant polycystic kidney disease.

## What does fibromuscular dysplasia look like on angiography?

A ‘string of beads’: narrowed ridges alternating with dilated segments.

## Why can a large arteriovenous fistula cause heart failure?

Blood bypasses the capillaries, so the heart must pump much more volume to keep tissues perfused (high-output failure).

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## Elsewhere in DurgiPedia

- [Aortic arch arteries and their derivatives](https://durgical.com/en/embryology/aortic-arch-arteries-and-their-derivatives/)
- [Blood vessels: artery, vein and capillary layers](https://durgical.com/en/histology/blood-vessels-artery-vein-and-capillary-layers/)

## Connections

## Related 3

- [Aneurysms: types and pathogenesis](https://durgical.com/en/general-pathology/aneurysms-types-and-pathogenesis/)
- [Vascular ectasias](https://durgical.com/en/general-pathology/vascular-ectasias/)
- [Hypertension: mechanisms](https://durgical.com/en/general-pathology/hypertension-mechanisms/)

## Related conditions 4

- [Subarachnoid haemorrhage](https://durgical.com/en/conditions/subarachnoid-haemorrhage/)
- [Brain arteriovenous malformation](https://durgical.com/en/conditions/brain-arteriovenous-malformation/)
- [Renovascular hypertension (renal artery stenosis)](https://durgical.com/en/conditions/renovascular-hypertension/)
- [Hereditary haemorrhagic telangiectasia (Osler–Weber–Rendu)](https://durgical.com/en/conditions/hereditary-haemorrhagic-telangiectasia/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Subarachnoid Hemorrhage](https://www.ncbi.nlm.nih.gov/books/NBK441958/) (StatPearls (NCBI Bookshelf), 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/vascular-anomalies-berry-aneurysm-av-fistula-fibromuscular-dysplasia/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/vascular-anomalies-berry-aneurysm-av-fistula-fibromuscular-dysplasia/