In cases of vasculitis, magnetic resonance imaging usually shows multiple smaller subcortical ischemic areas in the white matter in both cerebral hemispheres. In some cases, typical irregularities in the vessel wall may already be seen on imaging (MRA, CTA, DSA), with stenotic and dilated segments. The final diagnosis is established by evidence of antibodies in serum and cerebrospinal fluid; a cerebral vessel biopsy is sometimes necessary. Treatment is determined by the underlying disease and may involve anti-inflammatory therapy or even immunosuppressive therapy.
One example of vasculopathy is moyamoya disease (moyamoya is Japanese for “foggy” or “smoky”), in which extremely fine, complex collateral networks form in the area of the perforating arteries when major cerebral arteries are occluded (see the section on surgical therapy below). Inflammatory diseases (e.g., meningitis) or neoplasia (e.g., meningioma at the base of the skull) may also lead to narrowing and occlusion of intracranial vessels. However, the main diagnosis in these cases is usually so obvious that differential-diagnostic considerations are secondary.
1.2.4 Imaging diagnosis
Ischemic cerebrovascular events present as transient, fluctuating, or permanent neurological deficits. Transient ischemic attack (TIA) has so far been defined clinically as a neurological deficit that lasts for up to a maximum of 24 hours. TIA leads to frank stroke within 90 days in over 10% of cases. In contrast to earlier approaches, rapid clarification and treatment within 24 hours are now recommended, and this reduces the risk of stroke to 2%. Imaging diagnosis must include either computed tomography (CT) or magnetic resonance imaging (MRI), or a combination of the two modalities. In patients with acute non-fluctuating deficit and significant loss of function, imaging should be carried out as quickly as possible in order to limit the damage caused by the ischemia.
To establish an indication for intravenous or intra-arterial thrombolysis or thrombectomy, noncontrast CT followed by CT angiography is usually sufficient. This makes it possible to distinguish hemorrhagic from ischemic stroke. In addition, treatment-relevant vascular occlusions can be quickly demonstrated (with an examination time of < 2 min). MRI is preferable to CT diagnosis in individual cases (e.g., unclear time window, young patient) in an acute setting, but it involves a longer examination time (approximately 15–20 min).
In addition to imaging of the area with diffusion disturbance or infarction and the underlying vascular pathology on MRI and CT, a perfusion study (CT and MRI) after bolus contrast administration may reveal underperfusion of the vascular territory involved. Intracranial stenoses may lead to fluctuating neurological deficits as a result of recurrent emboli or underperfusion. When there is a drop in systemic blood pressure, stenoses often have hemodynamic effects as a sign of an inadequate collateral supply. Clarification of the hemodynamic components before a treatment decision is taken (for endovascular or surgical treatment) thus requires perfusion measurements in order to assess the quality of the cerebral collateral supply (described in the section on surgical therapy below) and the perfusion reserve.
1.2.4.1 Doppler/color duplex ultrasonography
Examination technique
Transtemporal insonation of the distal internal carotid artery, carotid T, middle cerebral artery (M1/2), anterior cerebral artery (A1), and posterior cerebral artery (P1/2) is obligatory. The latter may be confused with the superior cerebellar artery when pulsed-wave Doppler is used, therefore visual stimulation should be carried out as a check (the posterior cerebral artery shows increased flow in response to inert optic stimuli after prior closing of the eye, due to supply of the visual cortex; the superior cerebellar artery shows no reaction).
Optionally, transtemporal imaging of the internal carotid artery may be carried out at cerebral levels and toward the base of the skull, as well as in the basilar artery and clivus if needed. Transnuchal insonation of the vertebral artery bilaterally, as well as of the basilar artery, is also obligatory, with imaging of the posterior inferior cerebellar artery (PICA) if needed. Transtemporal insonation is difficult in approximately 30% of cases and impossible due to a widened calvaria in 20% of cases; an ultrasound contrast medium may then be used → initial saturation artifact (“blooming”) can be corrected by reducing the transmission power (but not the gain; with a lower mechanical index, the contrast medium has a longer intravascular persistence). One milliliter of ultrasound contrast medium is often sufficient.
Differential diagnosis
Specific findings