Logo of extranstromedBioMed CentralBiomed Central Web Sitesearchsubmit a manuscriptregisterthis articleExperimental & Translational Stroke MedicineJournal Front Page
Exp Transl Stroke Med. 2010; 2: 4.
Published online Feb 4, 2010. doi:  10.1186/2040-7378-2-4
PMCID: PMC2827391

In vivo MRI assessment of permanent middle cerebral artery occlusion by electrocoagulation: pitfalls of procedure

Abstract

Permanent middle cerebral artery (MCA) occlusion (pMCAO) by electrocoagulation is a commonly used model but with potential traumatic lesions. Early MRI monitoring may assess pMCAO for non-specific brain damage. The surgical steps of pMCAO were evaluated for traumatic cerebral injury in 22 Swiss mice using diffusion and T2-weighted MRI (7T) performed within 1 h and 24 h after surgery. Temporal muscle cauterization without MCA occlusion produced an early T2 hyperintensity mimicking an infarct. No lesion was visible after temporal muscle incision or craniotomy. Early MRI monitoring is useful to identify non-specific brain injury that could hamper neuroprotective drugs assessment.

Introduction

Investigating cerebral ischemia requires animal models relevant to human stroke. A precise knowledge of the strengths and shortcomings of available models is mandatory for effective research in neuroprotection [1,2]. Initially described in the rat [3] and subsequently adapted in mice [4], permanent middle cerebral artery (MCA) occlusion (pMCAO) by electrocoagulation is a widely used model of focal ischemia. Invasive surgical procedures are required: temporal muscle dissection, in some cases by electrical cauterization [5,6], subtemporal craniotomy and MCA electrocoagulation. This model, by interrupting blood flow at the level of the parietal cerebral artery branch of the MCA (distal occlusion), has the advantage of producing smaller, cortical-restricted, more reproducible and better-tolerated infarcts compared to suture MCAO, which endoluminal occluder is situated in the internal artery, at the birth of the MCA (proximal occlusion) and gives rise to extensive cortico-striatal infarcts [7,8]. It may however induce traumatic brain damage.

To our knowledge, sham-operated animals have only been studied using immunohistology at the subacute stage of cerebral ischemia. Early monitoring with magnetic resonance imaging (MRI) may facilitate in vivo identification of traumatic brain injury during pMCAO.

Materials and methods

Animals and surgical procedure

We designed an analytic appraisal of pMCAO procedure which included two methods of temporal muscle dissection: cauterization and blade incision. After intraperitoneal anesthesia with 12 mg/Kg xylazine and 90 mg/Kg ketamine, 22 male Swiss mice (28-30 g, Charles River, France) were allotted as follows:

• group A (n = 6): temporal muscle cauterization without craniotomy nor MCA occlusion;

• group B (n = 4): temporal muscle incision without craniotomy nor MCA occlusion;

• group C (n = 4): temporal muscle incision followed by craniotomy without MCA occlusion;

• group D (n = 6): temporal muscle incision followed by craniotomy and MCA electrocoagulation;

• group E (n = 2): temporal muscle cauterization followed by craniotomy and MCA electrocoagulation.

Craniotomy and MCA electrocoagulation were performed as previously described [9]. Whatever the group be, surgery was performed in less than 15 min.

MRI

MRI experiments were performed on a 7T/12 cm magnet (Bruker BioSpin GmbH, Ettlingen, Germany) using a 72 mm inner diameter birdcage for RF transmission and a 15 mm diameter surface coil for reception. T2-weighted images (T2WI) were acquired using a RARE sequence with TE/TR = 75/3000 ms. Diffusion weighted spin-echo images (DWI) were acquired with a TE/TR = 14/2000 ms using 2 b-values (139 and 1061 s/mm2). Apparent diffusion coefficients (ADC, in mm2/s) were calculated by fitting a monoexponential model function on a pixel-by-pixel basis. The field of view was 20 × 20 mm2 and slice thickness 1.0 mm. For T2WI, 15 slices were acquired with 256 × 256 matrix and for DWI, 7 slices with 128 × 128 matrix. Mice anesthesia was maintained during the MRI with isofluorane (1.5% in air). Body temperature was kept at 37 ± 1°C with an integrated heating system, and a pressure probe monitored mice respiration. MRI was started immediately following the end of surgical procedure and all MR acquisitions were performed between 30 min and 60 min after the start of surgery. MRI was repeated on day 1.

Results

Temporal muscle cauterization in the absence of MCA electrocoagulation (group A) consistently produced an extensive lesion across the frontoparietal cortex (n = 6/6). These lesions appeared hyperintense on T2WI within the first hour after surgery, with an early mass effect and reduced ADC (Figure (Figure1A).1A). Temporal muscle incision and craniotomy in the absence of MCA electrocoagulation (group B and C, respectively) caused no visible brain injury on day 0 or day 1 MRI (n = 4/4 in groups B and C, Figure Figure1B1B and and1C).1C). MCA electrocoagulation (group D) induced an ischemic lesion in the frontoparietal cortex with reduced ADC on day 0 (n = 6/6). These lesions were not visible on T2WI within 1 h post-surgery (Figure (Figure1D).1D). No bleeding was noted during the surgery, but MCA electrocoagulation occasionally produced a small superficial traumatic lesion (n = 2/6 in group D, figure figure1D).1D). When pMCAO was performed using temporal muscle cauterization (group E), the lesion appeared as a superimposition of the almond-shaped cauterization lesion and of the MCA-territory bounded ischemic lesion (n = 2/2, Figure Figure2).2). Infarcts from group A, D and E were clearly delineated on day 1 T2WI.

Figure 1
MRI within one hour of surgery: T2WI (upper row) and ADC map (lower row). A: temporal muscle cauterization alone (group A). Note the lesion with early T2WI hyperintensity and reduced ADC (arrows). B: temporal muscle incision alone (group B). C: temporal ...
Figure 2
Impact of temporal muscle cauterization on pMCAO with T2WI. A: temporal muscle cauterization alone (group A) showing day 0 traumatic lesion (interrupted lines). B: temporal muscle cauterization, craniotomy and MCA electrocoagulation (group E). Color-coded ...

Discussion

Our results showed that temporal muscle cauterization in the absence of ischemic stimulus produced a hyperintense area on T2WI highly suggestive of traumatic injury. Indeed, T2 increase is not expected in ischemic lesions within the first hours of occlusion in adults, although early T2 increase has been reported in neonates after MCA electrocoagulation [10] or hypoxia-ischaemia [11]. Early mass effect is uncommon after ischaemia in the adult rat [12] or mouse [13]. Acute ADC decrease is not specific of ischemic insult and has been described in both experimental and human traumatic brain injury [14,15]. Signal suggestive of intra- or extra-cranial surgery-related bleeding (T2 hypointensity) would have been ascertained using T2*WI, but were not noted. No traumatic injury was observed after temporal muscle incision. Accordingly, incision should be preferred over cauterization for temporal muscle dissection.

The MRI appearance of lesions resulting from both temporal muscle cauterization (traumatic damage) and occlusion (ischemic damage) may mimic an infarction, especially if imaging is done at later time points. Histopathological analyses are usually performed after a delay of 24-72 h, when traumatic and ischemic damage may not be discernable, while early histological examination of intracerebral coagulation necrosis would be required to ascertain the thermal origin of traumatic damage induced by muscle cauterization.

In the last decade, high resolution MRI has become a valuable tool for monitoring tissue damage in rodent models of cerebral ischemia. Early MRI monitoring may help to identify non-specific brain injury that could hamper neuroprotective drugs assessment.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

FC carried out the MRI experiments, participated in the design of the study and helped to draft the manuscript. SM carried out surgery. MW designed and optimized the MRI acquisition protocol, and helped to draft the manuscript. JCB participated in the MRI experiments. YB and NN conceived the study, and participated in its design and coordination. THC conceived the study, participated in its design, performed image analysis, and drafted the manuscript. All authors read and approved the final manuscript.

Acknowledgements

We are grateful to Jean-Baptiste Langlois, from the Small Animal Multimodal Imaging Facility, Animage (CERMEP, Lyon, France) for his help in MRI experiments.

References

  • Gladstone DJ, Black SE, Hakim AM. Toward wisdom from failure: lessons from neuroprotective stroke trials and new therapeutic directions. Stroke. 2002;33:2123–2136. doi: 10.1161/01.STR.0000025518.34157.51. [PubMed] [Cross Ref]
  • Liu S, Zhen G, Meloni BP, Campbell K, Winn R. J Exp Stroke Transl Med. 1. Vol. 2. 2009. Rodent stroke model guidelines for preclinical stroke trials; pp. 2–27. [PMC free article] [PubMed]
  • Tamura A, Graham DI, McCulloch J, Teasdale GM. Focal cerebral ischaemia in the rat: 1. Description of technique and early neuropathological consequences following middle cerebral artery occlusion. J Cereb Blood Flow Metab. 1981;1:53–60. [PubMed]
  • Welsh FA, Sakamoto T, McKee AE, Sims RE. Effect of lactacidosis on pyridine nucleotide stability during ischemia in mouse brain. J Neurochem. 1987;49:846–851. doi: 10.1111/j.1471-4159.1987.tb00971.x. [PubMed] [Cross Ref]
  • Boutin H, Dauphin F, MacKenzie ET, Jauzac P. Differential time-course decreases in nonselective, mu-, delta-, and kappa-opioid receptors after focal cerebral ischemia in mice. Stroke. 1999;30:1271–1277. [PubMed]
  • Herrmann O, Baumann B, de Lorenzi R, Muhammad S, Zhang W, Kleesiek J, Malfertheiner M, Kohrmann M, Potrovita I, Maegele I, Beyer C, Burke JR, Hasan MT, Bujard H, Wirth T, Pasparakis M, Schwaninger M. IKK mediates ischemia-induced neuronal death. Nat Med. 2005;11:1322–1329. doi: 10.1038/nm1323. [PubMed] [Cross Ref]
  • Carmichael ST. Rodent models of focal stroke: size, mechanism, and purpose. NeuroRx. 2005;2:396–409. doi: 10.1602/neurorx.2.3.396. [PMC free article] [PubMed] [Cross Ref]
  • Durukan A, Tatlisumak T. Acute ischemic stroke: overview of major experimental rodent models, pathophysiology, and therapy of focal cerebral ischemia. Pharmacol Biochem Behav. 2007;87:179–197. doi: 10.1016/j.pbb.2007.04.015. [PubMed] [Cross Ref]
  • Pialat JB, Cho TH, Beuf O, Joye E, Moucharrafie S, Langlois JB, Nemoz C, Janier M, Berthezene Y, Nighoghossian N, Desvergne B, Wiart M. MRI monitoring of focal cerebral ischemia in peroxisome proliferator-activated receptor (PPAR)-deficient mice. NMR Biomed. 2007;20:335–342. doi: 10.1002/nbm.1157. [PubMed] [Cross Ref]
  • Fau S, Po C, Gillet B, Sizonenko S, Mariani J, Meric P, Charriaut-Marlangue C. Effect of the reperfusion after cerebral ischemia in neonatal rats using MRI monitoring. Exp Neurol. 2007;208:297–304. [PubMed]
  • Qiao M, Latta P, Meng S, Tomanek B, Tuor UI. Development of acute edema following cerebral hypoxia-ischemia in neonatal compared with juvenile rats using magnetic resonance imaging. Pediatr Res. 2004;55:101–106. doi: 10.1203/01.PDR.0000100477.59081.FE. [PubMed] [Cross Ref]
  • Rudin M, Baumann D, Ekatodramis D, Stirnimann R, McAllister KH, Sauter A. MRI analysis of the changes in apparent water diffusion coefficient, T(2) relaxation time, and cerebral blood flow and volume in the temporal evolution of cerebral infarction following permanent middle cerebral artery occlusion in rats. Exp Neurol. 2001;169:56–63. doi: 10.1006/exnr.2001.7650. [PubMed] [Cross Ref]
  • Barber PA, Hoyte L, Kirk D, Foniok T, Buchan A, Tuor U. Early T1- and T2-weighted MRI signatures of transient and permanent middle cerebral artery occlusion in a murine stroke model studied at 9.4T. Neurosci Lett. 2005;388:54–59. doi: 10.1016/j.neulet.2005.06.067. [PubMed] [Cross Ref]
  • Marmarou A, Signoretti S, Fatouros PP, Portella G, Aygok GA, Bullock MR. Predominance of cellular edema in traumatic brain swelling in patients with severe head injuries. J Neurosurg. 2006;104:720–730. doi: 10.3171/jns.2006.104.5.720. [PubMed] [Cross Ref]
  • Unterberg AW, Stover J, Kress B, Kiening KL. Edema and brain trauma. Neuroscience. 2004;129:1021–1029. doi: 10.1016/j.neuroscience.2004.06.046. [PubMed] [Cross Ref]

Articles from Experimental & Translational Stroke Medicine are provided here courtesy of BioMed Central
PubReader format: click here to try

Formats:

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...

Links

  • MedGen
    MedGen
    Related information in MedGen
  • PubMed
    PubMed
    PubMed citations for these articles

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...