Why is a noncontrast CT head the first imaging study in suspected acute stroke?

It is fast and reliably detects intracranial hemorrhage. The decision that drives early management is ischemia versus bleed, because thrombolytics are catastrophic in a hemorrhagic stroke. An early ischemic infarct is often invisible on the initial CT, so a normal scan in the right clinical setting does not exclude ischemia and still permits treatment.

What is the time window for IV alteplase in ischemic stroke, and from when is it measured?

IV alteplase is given within 4.5 hours of the last known well time, not the time symptoms were discovered. If a patient wakes with deficits, the last known well is when they were last seen normal. Beyond that window, or when the last known well is unknown, mechanical thrombectomy for a large vessel occlusion can still be offered to selected patients up to 24 hours based on advanced imaging.

How is blood pressure managed around thrombolysis in acute ischemic stroke?

Before alteplase, blood pressure must be lowered to below 185/110 mmHg to reduce hemorrhage risk. In a patient who is not a thrombolysis candidate, permissive hypertension is allowed and pressure is generally not treated unless it exceeds roughly 220/120 mmHg, because the ischemic penumbra depends on perfusion.

Clinical Images

CT brain showing acute ischemic stroke hypodensity

CT hypodensity in MCA territory · noncontrast CT rules out bleed before tPA

Home Neuro Acute Ischemic Stroke

Acute Ischemic Stroke Management

Artery occludes → brain tissue dies by the minute. CT rules out bleed. tPA within 4.5 hours. Thrombectomy for large vessel occlusion. Every delay costs neurons.

A 71-year-old man with atrial fibrillation (not on anticoagulation) is brought in 55 minutes after sudden right arm and leg weakness and garbled speech. BP 168/92. Fingerstick glucose 118. Noncontrast CT head shows no hemorrhage and early loss of gray-white differentiation in the left MCA territory. CTA shows left M1 occlusion. NIHSS 14.

What is the best next step in acute management?

Start IV heparin drip

Activate stroke team: IV alteplase AND thrombectomy evaluation

Aspirin 325 mg and admit to stroke unit

MRI brain before any treatment

The Mechanism

Occlusion → Core vs Penumbra

Ischemic stroke is an artery blocked. The board wants the cause-effect chain from clot to salvageable tissue.

THE CLUE

Sudden focal neurologic deficit = think vascular territory until proven otherwise. An embolus from atrial fibrillation, a thrombus on a ruptured plaque, or a lacune in a penetrating arteriole all land the same way: no perfusion → energy failure → cell death.

BEATS

Artery occludes: blood stops reaching downstream brain. Neurons need glucose and oxygen every second.
Core dies fast: the center of the infarct loses ATP within minutes. That tissue is gone. You cannot resurrect it.
Penumbra hangs on: surrounding tissue is hypoperfused but still alive. This is the salvageable zone. Reperfusion (tPA or thrombectomy) saves penumbra before it becomes core.
Time is brain: roughly 1.9 million neurons lost per minute of untreated MCA occlusion. The clock starts at last known well (LKW), not when the CT finishes.
Reperfusion works: alteplase converts plasminogen to plasmin → plasmin digests fibrin → clot dissolves → flow returns. Mechanical thrombectomy pulls the clot out of large vessels (M1, ICA, basilar).

⚡ THE PUNCH: Ischemic stroke = blocked pipe. Core is dead, penumbra is dying. Your job is to reopen the pipe before penumbra becomes core. CT first to rule out bleed. Then lyse or retrieve.

⚠

Hemorrhagic transformation is not a reason to skip CT

Giving tPA into a hemorrhagic stroke can kill. Noncontrast CT head is mandatory before thrombolysis. MRI is more sensitive for early ischemia but must not delay treatment when the patient is in the tPA window.

Bedside & Workup

Presentation, NIHSS, and the CT Rule

Sudden onset focal deficits. Know what to measure and what to order first.

Presentation clues

Sudden onset: maximal deficit at onset (vs gradual tumor or metabolic decline).
FAST screen: Face droop, Arm drift, Speech slurred, Time to call stroke code.
Lateralization: left MCA → right face/arm > leg + aphasia if dominant hemisphere. Right MCA → left weakness + neglect.
Posterior circulation: vertigo, diplopia, ataxia, crossed findings. Basilar occlusion = locked-in trap.
NIHSS: quantifies stroke severity (0 to 42). Higher score → bigger deficit → more urgency for reperfusion.

Noncontrast CT head

First imaging study. Goal: rule out intracranial hemorrhage before tPA.

Early ischemic changes (loss of gray-white differentiation, sulcal effacement) support the diagnosis but a negative CT does NOT exclude ischemic stroke.

Glucose, BMP, CBC, coags

Fingerstick glucose immediately. Hypoglycemia mimics stroke. Check INR/platelets before tPA.

tPA contraindicated if glucose <50 or >400, INR >1.7, platelets <100,000, or active bleeding.

CT angiography (CTA)

Identifies large vessel occlusion (LVO): M1 MCA, ICA, basilar. LVO → thrombectomy candidate.

CTA should not delay IV alteplase when the patient is eligible. Run both in parallel when possible.

MRI with DWI (later or parallel)

Most sensitive for acute ischemia. Useful for wake-up strokes with advanced imaging selection.

Do not let MRI block the 4.5-hour tPA window when CT already ruled out bleed and LKW is known.

⚠

Todd paralysis after seizure

Focal weakness after a witnessed seizure that resolves over hours is Todd paralysis, not stroke. No tPA. Witnessed seizure + improving deficit = different pathway.

Treatment

tPA, Thrombectomy, BP, and Antiplatelets

The order and timing decide outcomes. Tap the acute pathway in the correct sequence.

Acute Ischemic Stroke Pathway

Tap the steps in the correct order for a patient in the thrombolytic window with no bleed on CT.

STEP 1

empty

STEP 2

empty

STEP 3

empty

STEP 4

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IV alteplase (tPA) essentials

Window: within 4.5 hours of LKW for most patients (3 hours is the classic cutoff; 3 to 4.5 hours has additional exclusion criteria).
Dose: 0.9 mg/kg (max 90 mg). Weight in kilograms. Board traps love pound-to-kg conversion errors.
BP before tPA: must be <185/110 (treat if higher, then lyse).
After tPA: keep BP <180/105 for 24 hours. Aspirin/defer antiplatelet ~24 hours unless no tPA given.
Mechanism: tissue plasminogen activator → plasminogen → plasmin → fibrin clot breakdown.

Mechanical thrombectomy

Indication: large vessel occlusion (M1, ICA, basilar) with significant deficit.
Window: up to 24 hours in selected patients with favorable imaging (penumbra salvageable on CTP/MRI).
Both, not either: give IV tPA first when eligible, then proceed to thrombectomy for LVO. Do not skip tPA just because thrombectomy is coming.

A patient arrives 2 hours after stroke onset. CT shows no hemorrhage. BP is 192/104. What must happen before IV alteplase?

BP gate. Systolic ≥185 or diastolic ≥110 is a relative contraindication until treated. Use IV labetalol or nicardipine, then lyse. Break it down: BP <185/110 before tPA. After tPA keep <180/105.

Same patient has left M1 occlusion on CTA and received alteplase. Best next step?

LVO needs retrieval. tPA alone often fails in M1 occlusions. Thrombectomy dramatically improves outcomes. Anticoagulation for AF is deferred days to weeks depending on infarct size. Break it down: tPA plus thrombectomy for eligible LVO. Anticoagulation later.

💉 Secondary prevention after stabilization: high-intensity statin, BP control, diabetes management, carotid revascularization if symptomatic stenosis, and anticoagulation for AF once hemorrhagic risk allows (often 4 to 14 days post stroke depending on size).

Prove It

Board Walkthrough

8-vignette bank, 5 dealt per round, answer choices shuffled, never-repeat within a round.

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Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last reviewed June 2026

Bone Wizardry is an independent educational resource for visual learning in the medical sciences. It is not affiliated with, endorsed by, or sponsored by any licensing or examination board, contains no real or recalled examination questions, and does not guarantee any educational or examination outcome.