Berry aneurysm
Formal Definition
Berry aneurysm (also called saccular aneurysm) — a focal, thin-walled outpouching of a cerebral artery, typically arising at arterial bifurcations in the circle of Willis with the strongest predilection for the anterior communicating artery complex, posterior communicating artery, and middle cerebral artery bifurcation; characterized histologically by absence of the tunica media at the aneurysm neck, leaving only intima and adventitia; clinically silent until rupture, which produces subarachnoid hemorrhage (SAH) with characteristic sudden "worst headache of life," possible loss of consciousness, nuchal rigidity, and high mortality/morbidity; common associations include ADPKD, Ehlers-Danlos type IV, and family history.
How It's Used on the Ward
"Berry aneurysm" or "cerebral aneurysm" — a bubble-like outpouching in the cerebral arteries that can rupture and cause a bleed into the subarachnoid space; the classic "thunderclap headache" (sudden, worst headache of life, sometimes with vomiting and loss of consciousness) is the warning sign; contrast is fusiform aneurysm (a longer dilation) and mycotic aneurysm (from infection).
Example
""52-year-old woman with ADPKD presents to ED with abrupt onset severe headache 90 minutes ago while exercising, vomiting x3, photophobia, brief loss of consciousness reported by bystanders. GCS 14 on arrival (E3 V5 M6), no focal deficit, neck stiffness on exam. Non-contrast CT head: hyperdense blood filling the basal cisterns and sulci (diffuse SAH pattern). CT angiography: 7 mm saccular aneurysm at the anterior communicating artery. Diagnosis: ruptured berry aneurysm with subarachnoid hemorrhage. Plan: neurosurgical consult for aneurysm securing (surgical clipping vs endovascular coiling), ICU admission for neuro checks, BP and ICP optimization, nimodipine for vasospasm prophylaxis, electrolyte and seizure monitoring.""
Clinical Context
Epidemiology: ~2–5% of adults harbor an unruptured berry aneurysm; rupture risk ~1% per year for aneurysms 7–10 mm, higher with prior SAH, family history, smoking, hypertension, and connective tissue disease. Risk factors (modifiable): smoking, hypertension, heavy alcohol. Risk factors (non-modifiable): female sex, age 40–60, family history (1st-degree relative with SAH), ADPKD, Ehlers-Danlos syndrome type IV, fibromuscular dysplasia, coarctation of the aorta. Screening: generally not population-wide; considered for high-risk families (2+ first-degree relatives with SAH) and patients with ADPKD planning major activities. Treatment of unruptured aneurysm: controversial; small (<7 mm) in low-risk locations may be observed; larger, growing, or symptomatic aneurysms warrant endovascular coiling or surgical clipping. Post-rupture care: ICU with neuro checks, BP control, euvolemia, nimodipine for vasospasm prevention (14-day course), seizure prophylaxis, surgical or endovascular aneurysm securing within 24–72 hours, trans-cranial Doppler monitoring for vasospasm, ICU stay 14–21 days for highest vasospasm risk. Complications: re-bleeding (highest in first 24 hours), vasospasm with delayed ischemic neurologic deficit (DIND) days 4–14, hydrocephalus requiring EVD/shunt, hyponatremia (SIADH vs CSW), seizures.