Central nervous system disorders

IV./3.3.: Magnetic resonance imaging – MR

IV./3.3.1.: Role of MR in the diagnostics of SAH

To certify the suspicion of SAH in acute phase, FLAIR (fluid attenuated inversion recovery) sequence can be applied. The freshly effused blood has a high signal intensity at this time, and it can be easily differentiated from the hypointensity of subarachnoid space. However, MR examination is only rarely performed in acute phase, because CT is easier accessible and trustworthy. In case of this patient group, whose members frequently suffer from very severe conditions, additional advantage of CT is its better accessibility to patients in order the life functions to be better monitored and supported during the examination.

Layout of the hemorrhage – FLAIR-hyperintensity – is equal to that of CT, and can resemble the signal intensity and layout of extensive meningitis very much. In addition, appearence of carcinomatous meningeosis can be also illusive, if the patient – either formerly due to a certain reason – received Gadolinium (Gd) contrast agent, taking into account that tumor tissue also enhances!

In subacute phase by progress of time MR becomes more and more trustworthy in contrast to CT. On CT, hyperdensity is increasingly regressive, whilst MR also demonstrates the hemoglobin decomposition products exceedingly in any phase of the decomposition. In case of follow-up, detection of hemoglobin decomposition products can be aimed– leptomeninx-attached iron deposition can be demonstrated on T2 weighted (T2*) and GE (gradiens echo) images best. This strength of MR underscores the opinion that MR scan should be performed in case of a negative CT scan and very strong clinical suspicion of SAH (e.g. if the result of lumbal punction is positive, viz. blood is in the liquor), and in cases if no CT examination has been performed for one week – 10 days following the development of symptoms.

IV./3.3.2.: MR angiography (MRA)

MR angiography detects not only the aneurysms but also the other, SAH-causing vascular lesions as well. Imaging of the very tiny (under 5 mm) aneurysm is absolutely not trustworthy (e.g. in case of agitated patient).