What does a round brain appearance on a computed tomography (CT) scan indicate?

Round Brain Appearance on CT Scan

Primary Interpretation

A "round brain" appearance on CT scan most commonly indicates loss of normal sulcal markings and gyral contours due to diffuse cerebral edema, which represents a critical finding requiring urgent evaluation for elevated intracranial pressure and its underlying cause. 1

Key Imaging Characteristics

The round brain appearance reflects:

• Loss of normal cortical sulci and gyral patterns due to brain swelling compressing the subarachnoid spaces 1
• Effacement of the basal cisterns, which appears as "tight basal cisterns" on imaging and indicates significant mass effect 1
• Reduced differentiation between gray and white matter from diffuse edema 1
• Potential compression of the ventricular system depending on severity 1

Clinical Significance and Urgency

This finding indicates significant brain shift or elevated intracranial pressure that contraindicates immediate lumbar puncture and requires urgent management 1. The round appearance signals that normal brain architecture is compromised by pathologic processes causing diffuse swelling.

CT scan is not a reliable tool for diagnosing raised intracranial pressure per se, but specific findings like tight basal cisterns and loss of sulci indicate dangerous elevations 1.

Differential Diagnosis to Consider

The round brain appearance warrants immediate investigation for:

• Intracranial hemorrhage (subdural, epidural, subarachnoid, or intraparenchymal) 1
• Acute ischemic stroke with significant edema 1, 2
• Intracranial mass lesions (tumor, abscess) causing mass effect 1
• Encephalitis (particularly HSV encephalitis which shows abnormalities in 80% of initial CT scans) 1
• Traumatic brain injury with diffuse axonal injury or contusions 1
• Hydrocephalus causing ventricular enlargement and periventricular edema 1
• Hypertensive emergency with posterior reversible encephalopathy syndrome 1

Immediate Management Algorithm

When encountering a round brain on CT:

1. Assess for signs of herniation including altered consciousness (GCS <13), abnormal posturing, pupillary abnormalities, or focal neurologic deficits 1

2. Defer lumbar puncture if this finding is present, as it represents a contraindication due to risk of herniation 1

3. Initiate measures to reduce intracranial pressure including head elevation, hyperventilation if indicated, and osmotic therapy as clinically appropriate 1

4. Determine the underlying etiology through clinical correlation, laboratory studies, and consideration of contrast-enhanced imaging 1

Role of Advanced Imaging

MRI brain without and with contrast should be obtained when CT is unrevealing regarding etiology or when higher sensitivity is needed for detecting:

• Small ischemic infarcts (MRI detects 70% of strokes presenting with altered mental status that CT misses) 2, 3
• Encephalitis (MRI should be performed within 24-48 hours for suspected cases) 3
• Subtle subarachnoid hemorrhage (MRI has 95% sensitivity when CT is negative) 3
• Underlying mass lesions causing the edema 3

Critical Pitfalls to Avoid

• Do not perform lumbar puncture when imaging shows significant brain shift, tight basal cisterns, or mass effect, as this can precipitate herniation 1
• Do not assume the absence of papilledema excludes elevated intracranial pressure—imaging findings take precedence 1
• Do not delay neurosurgical consultation when this finding is identified, as it may require urgent intervention 1
• Do not attribute the finding to "normal aging"—a truly round brain represents pathology requiring explanation 1