Subarachnoid hemorrhage

Imaging description Acute hemorrhage in the subarachnoid space appears as areas of hyperdensity in the basal cisterns, cerebral sulci, and/or the ventricles. There are several imaging findings that can help locate the site of a ruptured aneurysm. The distribution of blood in the subarachnoid space and thickness of a localized clot can often help with such localization. Additionally, the presence of a parenchymal hematoma is one of the most significant predictors for evaluating the location of the ruptured aneurysm (Fig. 6.1). CTA is increasingly gaining popularity as the procedure of choice for initial, and in a majority of cases definitive, evaluation (Fig. 6.2). The advantages of CTA include its near-uniform availability, safety profile, high spatial resolution, and limited time required to perform the test. Additionally, it can be obtained at the same sitting when the patient gets the non-contrast CT. CTA has the ability to demonstrate the precise relationship between bony structures of the skull and the aneurysm. CTA may also help demonstrate other characteristics of the aneurysm that are less well studied on digital subtraction angiography (DSA) – for example, presence of endoluminal thrombus as well as calcification of the aneurysm wall. Preoperative knowledge of these aneurysm characteristics significantly aids in therapeutic decisions. The reported overall sensitivity of CTA exceeds 90% when compared with DSA in most recent publications [1]. However, if there is any doubt regarding the findings on CTA, one should have a low threshold for recommending further evaluation with a DSA.