Intracortical Infarcts in Small Vessel Disease
A Combined 7-T Postmortem MRI and Neuropathological Case Study in Cerebral Autosomal-Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy
Background and Purpose—The purpose of this study was to report the detection of infarcts of the cerebral cortex in a patient with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) using high-resolution postmortem 7-T MRI in association with pathological examination.
Methods—Whole brain high-resolution MRI data were obtained postmortem at 7 T in a 53-year-old patient with CADASIL. These MRI data were used to guide the neuropathological examination of the cortex.
Results—Combined with neuropathology, MRI allowed the delineation of intracortical infarcts confirmed by histological examination in this case. These lesions were not visible on the last in vivo MRI obtained at 1.5 T and were difficult to detect on neuropathological examination only.
Conclusions—Postmortem high-resolution MRI may help to detect intracortical infarcts in CADASIL and possibly in other small vessel diseases of the brain.
Some data suggest that the cerebral cortex may be involved in small vessel disease (SVD) of the brain related to age, hypertension, and diabetes.1,2 In those SVDs, like in cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), microinfarcts and neuronal apoptosis have been described in postmortem pathological studies.3
Such microscopic structural changes might be extremely difficult to see in vivo because imaging techniques such as standard MRI (<3 T) do not provide adequate spatial resolution4 and ex vivo because microscopic examination cannot cover the whole brain so that small scattered lesions are easily missed. Ultrahigh-field MRI, however, has the potential to offer adequate spatial resolution for the detection of very small focal ischemic or hemorrhagic lesions within the cerebral cortex in SVD. We report a postmortem MRI study performed in a patient with CADASIL on a 7-T MRI scanner in combination with subsequent pathological examination.
A 53-year-old patient had been followed in Lariboisière Hospital since 2006. He presented with a progressive cognitive decline at the age of 40 years. After his first stroke at age 50 years (left hemiparesis of acute onset), his Mini-Mental State Examination score was 21, his Mattis dementia rating scale 127, and his modified Rankin Scale score 1. The patient underwent 2 clinical MRI scans (in May 2006 and December 2008) after the genetic test of CADASIL had confirmed the presence of a typical mutation in the Notch3 gene. Compared with the whole cohort (288 patients), lesion loads on MRI were high (lacunar lesion volume, 3865 mm3 on first MRI and 4407 mm3 on second, above the 95th percentile; white matter lesion volume, 84737 mm3 on first MRI and 117 803 mm3 on second, above the 55th percentile; microhemorrhage number, 1 on first MRI, 2 on second, above the 70th percentile; Figure 1). After a second stroke at age 53 years, his clinical status rapidly worsened. The patient died 6 months later from complications of a urinary tract infection. The patient gave his informed consent to participate in this study, which was approved by a local ethics committee.
MRI and Image Processing and Analysis
The MRI protocol used in vivo has been previously reported.5 Postmortem MRI was performed using a 7-T clinical MRI scanner (Siemens, Erlangen, Germany) equipped with a head gradient insert coil (80 mT/m, 333 T/m/s) and an 8-channel head coil. The brain was contained in an hermetic plastic cylinder filled with a 10% buffered formalin solution and tightly maintained between hydrophilic textile sheets. High-resolution 3-dimensional T2* (HR-MRI) sequences were acquired through 3 contiguous slightly overlapping blocks; field of view=192 mm; 176 slices; slice thickness=300 μm; in-plane matrix 640×640 leading to an isotropic spatial resolution of 300 μm; repetition time TR=40 ms; echo time TE=15 ms; flip angle=20°; read bandwidth=80 Hz/pixel; averaging number of excitations=4, total acquisition time: 12 hours. Low-resolution 2-dimensional T2* sequences were acquired through 7 contiguous slightly overlapping blocks, field of view=268 mm; 20 slices; slice thickness TH=700 μm; in-plane matrix 384×384; repetition time TR=900 ms; echo time TE1/TE2=13.7/29.9 ms; flip angle=65°; read bandwidth=70 Hz/pixel; averaging number of excitations=2, total scan time: 43 minutes.
Autopsy was performed 3 hours after death and was limited to the brain. MRI acquisitions were made after 1 month of 10% buffered formalin fixation followed by macroscopic examination on 1-cm thick coronal sections of the cerebral hemispheres and of the brain stem with the cerebellum perpendicular to its long axis. Those involving the cerebral hemispheres were embedded in paraffin and 15-μm thick sections were stained by hematoxylin and eosin and cresyl violet combined with Luxol fast blue (Klüver and Barrera stain). Smaller blocks of 3.0×2.0×0.5 cm were taken from the cerebral cortex with underlying white matter, basal ganglia, hypothalamus, midbrain, cerebellum, and brain stem. Additional samples were taken according to the results of HR-MRI. On selected 5-μm thick sections of samples from the frontal lobe at the level of the rostrum of corpus callosum (F1), occipital lobe at the level of the calcarine sulcus, hippocampus, basal ganglia, thalamus, and cerebellum, immunohistochemistry was performed using an avidin–biotin complex, peroxidase-based method with antibodies raised against the protein β-amyloid Aβ (monoclonal β/A4 amyloid protein; Dako Cytomation, Glostrup, Denmark; 1/100), the phosphorylated tau protein (monoclonal mouse antihuman PHF-τ, clone AT8; Innogenetics, Gent, Belgium;1/20), and Notch3 (monoclonal antibodies raised against N3ECD kindly provided by Dr A. Joutel, INSERM U270, Faculté de Médecine Lariboisière, Paris, France; 1/10).
HR-MRI revealed countless focal hypointensities scattered through the cortical mantle. The vast majority were hypointensities of linear shape with regular edges, a few hundred micrometers in diameter, crossing the cortical mantle on consecutive MRI slices. Those lesions actually corresponded to microvessels passing through the cortex. We also observed approximately 20 small hypointense foci of irregular shape and of signal intensity similar to that of white matter. Some of these lesions were round and did not reach the cortical mantle edges, whereas others were pyramidal with their bases lying on gray/white matter interface (Figure 2). Both lesions were present in all cerebral lobes, including the hippocampus (Figure 3). These lesions were more difficult to discern on low-resolution MRI (Figure 2). Histological examination showed that these lesions corresponded to intracortical infarcts. Few of these intracortical infarcts exhibited focal hemorrhages at their periphery, which were visible through small susceptibility artifacts on MRI (Figure 3). No “pure” microhemorrhage was detected within the cortex. Approximately 75% of these lesions were also seen on low-resolution MRI.
Immunochemistry did not identify foci of amyloid angiopathy either near the intracortical infarcts or in the remaining material, but instead typical arteriolar changes of CADASIL containing Notch3-positive material. They were particularly conspicuous in leptomeningeal arterioles in which granular material was also present (Figure 4). In the neighborhood of the 2 types of intracortical infarcts, lumen narrowing and extent of vessel wall damage were similar. We did not find any thrombotic material within the vessel lumen in either case. We also observed diffuse Aβ plaques and occasional amyloid plaques in the absence of overt tau pathology throughout the cerebral cortex. These changes differed from the typical Alzheimer disease changes as already reported in previous CADASIL cases.6
To our knowledge, this is the first description of intracortical infarcts in CADASIL as well as in SVD related to age, hypertension, and diabetes detected postmortem using both whole brain 7-T MRI and pathological examination. The use of HR-MRI improved the detection of intracortical infarcts at pathological examination because their small number and wide scatter through the whole cerebral cortex would render their detection difficult based on pathological examination only.
There is accumulating evidence suggesting a possible role of cortical microinfarcts (detectable only by histology) on cognitive function in different populations,1,2 but the clinical impact of such lesions is still unclear, whereas it is largely recognized in cerebral amyloid angiopathy, another type of SVD.7 The present results further support the importance of cortical lesions that are not visualized on conventional MRI in SVD.
At 7 T, most lesions detected with HR-MRI were also visible using low-resolution MRI, although they were more difficult to differentiate from microvessels. This suggests that 7-T MRI could be used also in vivo to detect intracortical infarcts within the cortex. We identified 2 subtypes of intracortical infarcts. Whether these different subtypes are related to distinct underlying mechanisms is unknown. The different diameter or length of the very short penetrating arteries supplying the corresponding areas may explain this finding.
This study has several limitations. The data were obtained in a single case but our choice was to exclude sliced material or tissue fixed for years with formalin due to potential heterogeneous consequences on the MR signal. The lack of a control sample also limits the interpretation of the results. The role of hypertension or of another SVD in this case cannot be totally excluded, although this appears unlikely because typical vascular alterations of CADASIL were detected in the close vicinity of intracortical infarcts in the absence of amyloid angiopathy. Moreover, the patient had no history of hypertension or diabetes, his blood pressure was normal at inclusion, and glycohemoglobin was 4.7%.
So far, the presence of lacunar lesions in deep brain structures has led to the hypothesis that the length of penetrating arterioles was a key determinant in the occurrence of ischemic lesions in SVD related to hypertension and diabetes. The presence of intracortical infarcts in a genetic model of SVD may indicate that the central role played by the length of arterioles was overestimated in SVD because lesions occurring in deep structures are easier to detect than few lesions scattered over the whole cortical mantle. Further systematic studies are thus needed to search for the presence of intracortical infarcts in different types of SVD.8 The results of this study suggest that high-resolution MRI can help their detection in postmortem cerebral tissue. Whether optimized in vivo sequences can be used to detect these lesions will also need further investigations.
Sources of Funding
This work was supported by PHRC grant AOR 02-001 (DRC/APHP) and performed with the help of ARNEVA (Association de Recherche en Neurologie VAsculaire), Hôpital Lariboisiere, France, “La Fondation Planiol,” and “La Fondation NRJ–Institut de France.” E.J. was supported by a grant from the “Fonds d'Etude et de Recherche du Corps Médical–FERCM” and the “Société Française de Neurologie–SFN.”
We thank Pr Anne Vital for her kind help.
- Received June 21, 2010.
- Revision received November 11, 2010.
- Accepted December 8, 2010.
- © 2011 American Heart Association, Inc.
- Gold G,
- Giannakopoulos P,
- Herrmann FR,
- Bouras C,
- Kövari E
- Viswanathan A,
- Gray F,
- Bousser MG,
- Baudrimont M,
- Chabriat H
- Jouvent E,
- Mangin JF,
- Porcher R,
- Viswanathan A,
- O'Sullivan M,
- Guichard J-P,
- Dichgans M,
- Bousser M-G,
- Chabriat H
- Schrag M,
- McAuley G,
- Pomakian J,
- Jiffry A,
- Tung S,
- Mueller C,
- Vinters HV,
- Haacke EM,
- Holshouser B,
- Kido D,
- Kirsch WM