What is the diagnosis in a 31-year-old man with headache, vomiting, and right homonymous hemianopia?

Diagnosis: Left Posterior Cerebral Artery (PCA) Stroke

The most likely diagnosis in this 31-year-old man presenting with headache, vomiting, and right homonymous hemianopia is an acute left posterior cerebral artery (PCA) stroke causing left occipital lobe infarction. 1, 2

Clinical Reasoning

Visual Field Defect Localization

• Right homonymous hemianopia indicates a lesion in the left postchiasmal visual pathway, most commonly the left occipital cortex supplied by the left PCA 1, 2
• The combination of headache, vomiting, and homonymous hemianopia strongly suggests acute vascular occlusion rather than a mass lesion 2
• In a cohort of 85 PCA stroke patients with homonymous hemianopia, 87% described the visual sensation as negative (loss of vision), and 66% correctly lateralized it to a hemifield in both eyes 2

Associated Symptoms Support PCA Territory Ischemia

• Headache and vomiting are common presenting symptoms in PCA stroke, occurring in 43% of patients alongside visual symptoms 2
• These symptoms reflect either increased intracranial pressure from venous congestion or involvement of structures beyond the visual cortex 2
• In PCA stroke patients, concurrent infarction commonly affects the temporal lobe, thalamus, and cerebellum, explaining nonvisual symptoms 2

Critical Differential Diagnosis to Exclude

Cerebral Venous Thrombosis (CVT)

• CVT must be urgently excluded as it can present identically with headache, vomiting, and homonymous hemianopia 3, 4
• CVT is particularly important to diagnose because treatment differs fundamentally (anticoagulation even with hemorrhage vs. standard stroke protocols) 3
• The American Heart Association emphasizes that headache occurs in 90% of CVT cases and can progress over days to weeks 3
• CVT should be suspected when headache precedes or accompanies focal neurological deficits, especially in younger patients 3, 4
• A 65-year-old woman with right homonymous hemianopia from left transverse sinus thrombosis initially had negative imaging, requiring repeat MRI and venography for diagnosis 4

Space-Occupying Lesions

• Brain tumor, abscess, or hemorrhage must be excluded, though the acute onset over hours (not days/weeks) makes these less likely 3
• The American College of Radiology recommends urgent neuroimaging to exclude mass lesions in patients with papilledema or signs of raised intracranial pressure 3

Idiopathic Intracranial Hypertension (IIH)

• IIH typically presents with headache, vomiting, and papilledema but would not cause homonymous hemianopia unless there is concurrent venous thrombosis 5
• The American Academy of Neurology states that IIH patients may have sixth nerve palsy but not other focal neurological deficits 5

Immediate Diagnostic Workup

Urgent Neuroimaging (Within Minutes)

• Non-contrast CT head immediately to exclude hemorrhage and assess for early ischemic changes 6
• CT angiography (CTA) or MR angiography (MRA) to identify PCA occlusion and determine eligibility for endovascular intervention 1
• CT or MR venography mandatory within 24 hours to exclude cerebral venous thrombosis 3, 5

Advanced Imaging if Initial CT Negative

• MRI brain with diffusion-weighted imaging (DWI) is more sensitive than CT for acute ischemia and will show high-intensity areas in the left occipital lobe 1
• MRI should show no evidence of hydrocephalus, mass, or abnormal meningeal enhancement 5
• If venous thrombosis is suspected but not clearly seen, 4-vessel angiography may be needed 4

Ophthalmologic Examination

• Formal visual field testing (Humphrey visual field test) to document the extent of hemianopia 4
• Dilated fundal examination to assess for papilledema, which would suggest increased intracranial pressure from CVT or mass effect 5

Time-Critical Treatment Considerations

Thrombolytic Therapy Window

• Intravenous thrombolysis (tPA) must be administered within 4.5 hours of symptom onset if no contraindications exist 1
• Endovascular thrombectomy can be performed up to 24 hours in selected patients with large vessel occlusion 1
• A 63-year-old man with acute PCA occlusion achieved complete recanalization 210 minutes after symptom onset with endovascular clot aspiration, resulting in complete recovery from homonymous hemianopia 1

If CVT is Diagnosed Instead

• Anticoagulation with parenteral heparin should be started immediately, even in the presence of hemorrhagic infarction 3, 4
• The American Heart Association recommends therapeutic heparin for CVT, as early anticoagulation prevents propagation of thrombus and improves outcomes 3

Common Pitfalls to Avoid

Delayed Diagnosis Due to Nonspecific Symptoms

• PCA strokes are often diagnosed late because symptoms can be subtle or attributed to other causes (e.g., migraine, sinusitis) 1, 7
• A 69-year-old man initially diagnosed with sinusitis at urgent care actually had PCA stroke with monocular temporal hemianopia 7
• Do not dismiss new-onset headache with vision changes as benign—neuroimaging is mandatory 7

Misinterpreting Visual Field Defects

• Patients may not spontaneously report homonymous hemianopia because they are unaware that both eyes are affected 2
• Specifically ask if vision loss affects the same side in both eyes to distinguish homonymous from monocular defects 2

Missing CVT on Initial Imaging

• CVT can have nonprominent lesions on initial CT or MRI, requiring repeat imaging or dedicated venography 4
• If clinical suspicion remains high despite negative initial imaging, repeat MRI in 2-3 days and obtain venography 4

Assuming Macular Sparing Rules Out Stroke

• Macular sparing occurs when the occipital pole receives collateral flow from the middle cerebral artery, preserving central 5-10° of vision 8
• The presence or absence of macular sparing does not change the diagnosis or urgency of treatment 8