Research Article: MR-angiography allows defining severity grades of cerebral vasospasm in an experimental double blood injection subarachnoid hemorrhage model in rats

Date Published: February 9, 2017

Publisher: Public Library of Science

Author(s): Vesna Malinova, Marios N. Psychogios, Ioannis Tsogkas, Birte Koennecke, Kim Bleuel, Bogdan Iliev, Veit Rohde, Dorothee Mielke, Nima Etminan.

http://doi.org/10.1371/journal.pone.0171121

Abstract

Magnetic resonance (MR) imaging has been used for the detection of cerebral vasospasm (VSP) related infarction in experimental subarachnoid hemorrhage (eSAH) in rats. Conventional angiography is generally used to visualize VSP, which is an invasive technique with a possible increase in morbidity and mortality. In this study we evaluated the validity of MR-angiography (MRA) in detecting VSP and its feasibility to define VSP severity grades after eSAH in rats.

SAH was induced using the double-hemorrhage model in 12 rats. In two rats, saline solution was injected instead of blood (sham group). MR was performed on day 1, 2 and on day 5. T1-, T2-, T2*-weighted and time-of-flight MR sequences were applied, which were analyzed by two blinded neuroradiologists. Vessel narrowing of 25–50% was defined as mild, 50–75% as moderate and >75% as severe VSP.

We performed a total of 34 MRAs in 14 rats. In 14 rats, MRA was performed on day 2 and day 5. In six rats MRA was additionally performed on day1 before the blood injection. A good visualization of cerebral vessels was possible in all cases. No VSP was seen in the sham group neither on day 2 nor on day 5. We found vasospasm on day 2 in 7 of the 14 rats (50%) whereas all 7 rats had mild and one rat had additionally moderate and severe vasospasm in one vessel, respectively. On day 5 we found vasospasm in 8 of the 14 rats (60%) whereas 4 rats had severe vasospasm, 1 rat had moderate vasospasm and 3 rats demonstrated mild vasospasm. In 4 of the 14 rats (30%) an ischemic lesion was detected on day 5. Three of these rats had severe vasospasm and one rat had mild vasospasm. Severe vasospasm on day 5 was statistically significant correlated with the occurrence of ischemic lesions (Fisher’s Exact test, OR 19.5, p = 0.03).

MRA is a noninvasive diagnostic tool, which allows a good visualization of the cerebral vasculature and provides reproducible results concerning the detection of VSP and the differentiation into three severity grades in rats. Future studies are needed to directly compare MRA with conventional angiography.

Partial Text

Cerebral vasospasm (VSP) is still one of the main reasons for delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (aSAH). Different animal models of experimental subarachnoid hemorrhage (eSAH) in rats have been established during the last years [1–5]. The double hemorrhage model has been used for the investigation of delayed VSP [4]. In order to increase the incidence and severity of VSP, a modified double hemorrhage model of eSAH was recently introduced, in which unilateral occlusion of the common carotid artery is additionally performed [5]. Up to date, digital subtraction angiography (DSA) is the gold standard for the diagnosis of vasospasm and has been already applied in different experimental studies in rats [4,6]. But, DSA is an invasive method, possibly leading to an increase of morbidity and mortality rates. Therefore, noninvasive diagnostic methods are warranted, which likewise allow a reliable diagnosis of VSP and the differentiation of VSP severity grades as well.

A total of 34 MRA scans were performed in 14 rats. Twelve rats were in the eSAH group and two rats in the sham group. All 14 rats underwent MRA on day 2 and on day 5. In six rats MRA was additionally performed on day1 before the blood injection. All 34 MRA scans allowed a good visualization of the circle of Willis. We found vasospasm on day 2 in 7 of the 14 rats (50%) whereas all 7 rats had mild and one rat had additionally moderate and severe vasospasm in one vessel territory, respectively. In four of these 7 rats only one vessel was affected by vasospasm, in one rat three vessels and in two rats vasospasm was seen in four vessels simultaneously. On day 5 we found vasospasm in 8 of the 14 rats (60%), whereas 4 rats had severe vasospasm, 1 rat had moderate vasospasm and 3 rats had mild vasospasm. Out of the four rats with severe vasospasm, three had severe vasospasm in two vessels simultaneously and one rat had severe vasospasm in one vessel and additionally moderate vasospasm in one vessel and mild vasospasm in one vessel, respectively. We found vasospasm neither on day 2 nor on day 5 in the two sham-group rats. The median diameter of the internal carotid artery on the MRA on day 1 was 0.7mm. The median diameter of the anterior cerebral artery, middle cerebral artery and basilar artery was 0.6mm. In 4 of the 14 rats an ischemic lesion was seen on the MRI scan on day 5. All four rats had vasospasm on day 5, whereas three of these rats had severe vasospasm and one rat had mild vasospasm. The rats with vasospasm on the MRA scan on day 5 had a 2.5 fold higher risk to develop ischemic lesions compared to the rats without vasospasm (Fisher’s Exact test, OR 2.5 p = 0.08). Severe vasospasm on day 5 was statistically significantly correlated to the occurrence of ischemic lesions (Fisher’s Exact test, OR 19.5, p = 0.03). The ischemic lesions were located mostly in the thalamus, the basal ganglia or in the hippocampus. Two rats had more than one ischemic lesion at the same time. The results are summarized in Table 2. The measurements of the vessel’s diameter are shown in Fig 1 (as an example of the MCA). Examples of mild and severe VSP and of an ischemic lesion are shown in Figs 1, 2 and 3, respectively. Tables 3 and 4 show the quantitative analysis of the vessel diameter of each vessel on day 1, day 2 and day 5, respectively.

In this study, we investigated the utility of MRA for the detection of experimental VSP as well as the possibility to distinguish between different severity grades of VSP in a double hemorrhage eSAH-model in rats. As rats compared to humans have a good collateral blood supply of the brain and a higher metabolism rate allowing a faster clearance of the blood from the subarachnoid space, it is more difficult to induce vasospasm by a single blood injection. To increase the rate of delayed vasospasm, blood was injected on two consecutive days and additionally the left common carotid artery has been occluded, thereby reducing the tolerance to ischemia in the rats. As a consequence, the modified double blood injection model is associated with a high mortality rate, but allows better than other models the investigation of delayed vasospasm.

MRA is a useful noninvasive diagnostic tool that enables the reliable diagnosis of cerebral VSP in an eSAH-model in rats. Furthermore, MRA allows differentiating between mild, moderate and severe VSP. Future studies are needed comparing MRA with DSA.

 

Source:

http://doi.org/10.1371/journal.pone.0171121