Neuroimaging and Multimodal Neuromonitoring
Imaging
Noncontrast CT identifies hemorrhage, midline shift, and the hyperdense vessel sign; the ASPECTS score quantifies early ischemic change. CT angiography demonstrates large vessel occlusion and aneurysm; CT perfusion distinguishes core from penumbra. MRI diffusion-weighted imaging is the most sensitive sequence for early infarction, and susceptibility-weighted imaging detects microbleeds. Cerebral venous thrombosis may show an empty delta sign on contrast CT and is confirmed by MR or CT venography. A normal early CT never excludes ischemia or venous thrombosis.
Neuromonitoring
Intracranial pressure is measured with an external ventricular drain (the reference standard, which also allows CSF drainage) or a parenchymal monitor, which drifts over time. Rising ICP waveforms with P2 exceeding P1 suggest poor compliance. Brain tissue oxygen below 15-20 mmHg indicates ischemia; the BOOST-II trial showed safety but no outcome benefit. Transcranial Doppler showing middle cerebral artery mean flow velocities above 120 cm/s suggests vasospasm, confirmed by a Lindegaard ratio above 3; without that ratio, hyperemia can mimic vasospasm. Pupillometry, continuous EEG, and jugular venous oximetry add complementary data.
Trap: treating a single ICP number rather than the trend and waveform, or diagnosing vasospasm by Doppler velocity alone in a hyperemic patient.
Rule of thumb: a normal CT within the first hours does not exclude stroke or venous thrombosis; repeat imaging or obtain vascular studies when the clinical picture is compelling.