Is a tiny hypodense focus in the basal ganglia on non‑contrast CT more indicative of an acute ischemic stroke or an old lacunar infarct?

Distinguishing Acute from Chronic Hypodense Basal Ganglia Lesions on Non-Contrast CT

A tiny hypodense focus in the basal ganglia on non-contrast CT is more likely to represent an old lacunar infarct rather than acute ischemic stroke, particularly if it is well-demarcated, round or ovoid, and the patient lacks corresponding acute neurological symptoms. 1

Key Imaging Characteristics That Favor Chronic Lacunar Infarct

• Sharp, well-defined margins strongly suggest a chronic lacunar infarct rather than acute ischemia, as acute infarcts typically show ill-defined borders with loss of gray-white differentiation 1
• Round or ovoid shape measuring less than 20mm in diameter and visible on only two CT sections is characteristic of established lacunar infarcts 1
• Absence of mass effect or surrounding edema indicates chronicity, as acute infarcts develop cytotoxic edema that causes sulcal effacement and tissue swelling 2

Why Acute Stroke is Less Likely

• Non-contrast CT significantly underestimates acute ischemia in the first 6 hours after symptom onset, with the initial CT appearing normal in up to 25% of patients with acute cerebellar infarction 2, 3
• Acute basal ganglia infarcts present with loss of gray-white differentiation and hypodensity of the caudate or lentiform nucleus, not as discrete tiny foci 2, 3
• Acute ischemic changes require hours to become visible on CT, with hypodensity typically not appearing until 6-24 hours after onset, whereas a well-defined tiny lesion suggests evolution over weeks to months 3, 4

Clinical Context is Critical

• Correlation with acute neurological symptoms is mandatory - if the patient presents with acute hemiparesis, sensory loss, or other focal deficits referable to the basal ganglia, the lesion may represent acute-on-chronic pathology requiring further imaging 5
• Progressive stroke symptoms are more common with acute large-vessel disease causing lacunar-sized infarcts than with pure small-vessel lacunar infarction 6
• Absence of corresponding acute clinical syndrome strongly favors a chronic silent lacunar infarct, which are commonly found incidentally in hypertensive patients 7, 1

Differential Diagnosis Considerations

• Dilated perivascular spaces (DPS) can mimic lacunar infarcts on CT, particularly in the putamen, and typically have smooth margins compared to the irregular margins of lacunar infarcts 7
• Multiple similar lesions in the basal ganglia and thalamus suggest chronic small-vessel disease rather than acute stroke 7, 6
• Hypertension history increases the likelihood of chronic lacunar infarcts, as 22 of 34 patients with CT-confirmed lacunae had systemic hypertension 1

When Additional Imaging is Mandatory

• MRI with diffusion-weighted imaging (DWI) is the gold standard for detecting acute ischemia, turning positive within minutes with high sensitivity and specificity, and should be obtained immediately if clinical suspicion for acute stroke remains high despite normal or equivocal CT 2, 3
• CT angiography should follow non-contrast CT immediately in suspected large vessel occlusion to guide endovascular therapy decisions, as basal ganglia infarcts can result from MCA occlusion 2, 3
• Do not rely solely on non-contrast CT to exclude acute ischemia in the first 6 hours, as early infarct signs may be subtle or absent, particularly in small deep structures 3, 4

Common Pitfalls to Avoid

• Never assume a tiny hypodense focus is acute without correlating with symptom onset timing and obtaining DWI-MRI if the patient is within the treatment window 3, 4
• Do not overlook that lacunar-sized infarcts can result from large-vessel disease requiring different management than pure small-vessel lacunar infarction, necessitating vascular imaging 6
• Recognize that beam hardening artifact in the posterior fossa can obscure small brainstem infarcts, so clinical suspicion should prompt MRI even with normal CT 3