A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 65-year-old male presents to the emergency room complaining of a severe headache. He developed a sudden-onset severe throbbing headache while watching a football game on television. His past medical history is significant for migraines and hypertension; however, he states that this headache is different from his normal migraine headaches. He has a 30 pack-year smoking history. His family history is notable for stroke in his mother and father. His temperature is 98.9°F (37.2°C), blood pressure is 150/90 mmHg, pulse is 100/min, and respirations are 14/min. On examination, he is oriented to person, place, and time. Neck motion is limited due to pain. Strength is 5/5 bilaterally in both the upper and the lower extremities and sensation is grossly intact across all the dermatomal distributions. Patellar, brachioradialis, and Achilles reflexes are 2+ bilaterally. The vessel that is most likely responsible for this patient’s condition directly branches off which of the following vessels?
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A
Anterior cerebral arteryCorrect. The most common site of berry aneurysm rupture (anterior communicating artery) branches directly off the anterior cerebral artery, which forms the connection that the AComm bridges between right and left.
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B
Maxillary arteryIncorrect. The maxillary artery is a terminal branch of the external carotid — it supplies the deep face and is not in the circle of Willis or implicated in SAH.
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C
Internal carotid arteryIncorrect. The internal carotid artery itself gives off the posterior communicating, anterior choroidal, ophthalmic, and terminates as ACA/MCA, but the AComm specifically arises from the ACA, not directly from the ICA.
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D
Posterior cerebral arteryIncorrect. The posterior cerebral artery contributes to the posterior circle of Willis via the PComm but does not give rise to the anterior communicating artery.
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E
Middle cerebral arteryIncorrect. The MCA is a frequent site of ATHEROsclerotic ischemic stroke and lacunar infarcts, but the anterior communicating artery (the most common berry aneurysm site) arises from the ACA, not the MCA.
↑ Tap an answer to reveal the reasoning
Answer: A. A sudden onset, severe, "thunderclap" headache ("worst headache of my life") that is DIFFERENT from his usual migraines, with neck stiffness, in an older smoker with hypertension and a family history of stroke, is the textbook presentation of SUBARACHNOID HEMORRHAGE (SAH) — most commonly from rupture of a SACCULAR (BERRY) ANEURYSM.
The most common location for berry aneurysms is the ANTERIOR COMMUNICATING ARTERY (~30–35%, often quoted as the #1 site), followed by the posterior communicating artery and the middle cerebral artery bifurcation. The anterior communicating artery DIRECTLY BRANCHES OFF THE ANTERIOR CEREBRAL ARTERY (it is a short connecting vessel between the right and left anterior cerebral arteries, completing the anterior part of the circle of Willis).
So the chain of reasoning the question requires:
1. Identify the disease: SAH from ruptured berry aneurysm.
2. Identify the most common aneurysm site: anterior communicating artery.
3. Identify the parent vessel from which the anterior communicating artery arises: anterior cerebral artery.
Risk factors for berry aneurysm: hypertension, smoking, ADPKD, Ehlers-Danlos type IV, Marfan, coarctation, family history. Diagnosis: non-contrast head CT (sensitive in first ~6 hours; sensitivity declines after that, when LP showing xanthochromia is needed). CT angiography or formal cerebral angiography locates the aneurysm. Treatment: surgical clipping or endovascular coiling.
**Why each option:**
**A.** Correct. The most common site of berry aneurysm rupture (anterior communicating artery) branches directly off the anterior cerebral artery, which forms the connection that the AComm bridges between right and left.
**B.** The maxillary artery is a terminal branch of the external carotid — it supplies the deep face and is not in the circle of Willis or implicated in SAH.
**C.** The internal carotid artery itself gives off the posterior communicating, anterior choroidal, ophthalmic, and terminates as ACA/MCA, but the AComm specifically arises from the ACA, not directly from the ICA.
**D.** The posterior cerebral artery contributes to the posterior circle of Willis via the PComm but does not give rise to the anterior communicating artery.