Systematic Interpretation of Non-Contrast CT Head

Initial Technical Assessment

• The American College of Radiology recommends adopting a structured anatomical approach that systematically evaluates blood, brain parenchyma, ventricles, and bone to avoid missing critical pathology in acute neurological presentations 1, 2, 3
• Verify technical adequacy by confirming adequate coverage from vertex to foramen magnum with contiguous 5-10mm thick sections parallel to the canthal-meatal line 4
• Check for motion artifact or beam hardening that may limit sensitivity, particularly in the posterior fossa where artifact can obscure small brainstem infarcts 5, 6

Step 1: Blood (Hyperdensity Assessment)

• The American College of Radiology recommends systematically searching for hemorrhage, as this is the primary indication for non-contrast CT in acute neurological presentations 1, 2, 7
• Scan all brain parenchyma for hyperdensity, checking intraparenchymal, subarachnoid, subdural, epidural, and intraventricular spaces 1, 2
• Look for hyperdense vessel signs indicating acute thrombus, though this requires correlation with clinical presentation 1
• Evaluate dural venous sinuses for hyperdensity suggesting venous thrombosis, though only 30% of venous sinus thrombosis cases show abnormalities on non-contrast CT 1

Step 2: Brain Parenchyma (Gray-White Differentiation)

• Systematically assess each vascular territory for early ischemic changes, as these determine treatment eligibility and prognosis 4, 7
• Apply the ASPECTS to quantify early infarct signs in the MCA territory, examining for loss of gray-white differentiation, sulcal effacement, and hypoattenuation 4, 7
• Recognize that CT significantly underestimates acute ischemia compared to MRI, with beam hardening artifact particularly limiting detection of small brainstem infarcts 2, 5, 6
• Identify hypodensity of the caudate nucleus, lentiform nucleus, insular ribbon, or cortical regions as markers of established ischemic core 7

Step 3: Cerebrospinal Fluid Spaces

• Examine ventricular size and configuration, as hydrocephalus requires urgent intervention 3, 8
• Compare ventricular size to prior studies when available, looking for acute enlargement suggesting obstructive hydrocephalus or shunt malfunction 8
• Assess for intraventricular hemorrhage, which complicates management and worsens prognosis 1, 8
• Evaluate temporal horns and third ventricle disproportionately, as early enlargement may indicate developing hydrocephalus 8

Step 4: Bone and Extracranial Structures

• Systematically review all visualized bone and soft tissues, as incidental findings may explain symptoms or require follow-up 5
• Examine for fractures, particularly in trauma settings where CT rapidly identifies skull fractures and foreign bodies 6
• Assess skull base foramina for erosion or expansion suggesting perineural tumor spread or chronic infection 5

Critical Pitfalls to Avoid

• Never rely solely on CT to exclude acute ischemia in the first 6 hours, as early infarct signs may be subtle or absent 4, 7
• Do not overlook posterior fossa pathology where beam hardening artifact significantly limits sensitivity 5, 6
• Remember that venous sinus thrombosis is missed on 70% of non-contrast CTs, requiring CTV or MRV for definitive diagnosis 1

When Non-Contrast CT is Insufficient

• Recognize that non-contrast CT serves primarily to exclude hemorrhage and detect large established infarcts, but MRI is superior for detecting acute ischemia, small hemorrhages, posterior fossa pathology, and chronic small vessel disease 1, 2, 7, 9
• Consider immediate MRI with DWI for suspected acute stroke when CT is normal but clinical suspicion remains high 7
• Add CTA immediately after non-contrast CT in suspected large vessel occlusion to guide endovascular therapy decisions 7
• Reserve contrast-enhanced CT only for specific concerns about infection, tumor, or inflammatory conditions, as it adds no value for routine stroke or hemorrhage evaluation 3, 8

Imaging Differentiation of Acute vs. Chronic Basal Ganglia Lesions on Non‑Contrast CT

Imaging Features Suggesting a Chronic Lacunar Infarct

• The lack of mass effect or surrounding edema on non‑contrast CT favors a chronic lacunar infarct, because acute infarcts typically produce cytotoxic edema that leads to sulcal effacement and tissue swelling. American Stroke Association 10

Limitations of Non‑Contrast CT in Detecting Acute Ischemia

• In the first 6 hours after symptom onset, non‑contrast CT frequently underestimates acute ischemia; the scan can appear completely normal in up to 25 % of patients with an acute cerebellar infarction. American Stroke Association 10

Acute Basal Ganglia Infarct Characteristics

• Acute basal‑ganglia infarcts usually manifest as loss of gray‑white differentiation and diffuse hypodensity of the caudate or lentiform nucleus, rather than as a tiny, well‑demarcated focus. American College of Cardiology 11

Recommended Advanced Imaging When Acute Stroke Is Suspected

• Diffusion‑weighted MRI is the gold‑standard for acute ischemia detection, turning positive within minutes and offering high diagnostic accuracy; it should be performed promptly when acute stroke cannot be excluded on CT. American College of Cardiology 11
• CT angiography should follow the non‑contrast scan in cases of suspected large‑vessel occlusion to inform endovascular treatment decisions, as basal‑ganglia infarcts may result from middle‑cerebral‑artery occlusion. American College of Cardiology 11

Chronic Basal Ganglia Hypodensity Represents Old Lacunar Infarcts

Imaging Findings in Chronic Cerebrovascular Disease

• Small hypodense areas in the basal ganglia on non‑contrast CT are frequently observed in patients with chronic cerebrovascular disease and correspond to old lacunar infarcts caused by occlusion of small penetrating arteries; evidence from a 2008 Stroke study. 12