pISSN 1598-298X
J Vet Clin 31(5) :457-460 (2014)
457
Magnetic Resonance Characteristics of Ischemic Brain Infarction in Three Dogs
Ki-Ja Lee, Young-Whan Kim*, Sung-Jin Choi**, Soo-Young Choi***, In-Seong Jeong*, Ho-Jung Choi*** and Young-Won Lee***1 College of Veterinary Medicine, Kyungpook National University, Daegu 702-701, Korea
*Royal Animal Medical Center, Seoul 131-878, Korea
**Department of Veterinary Surgery, The University of Tokyo, Tokyo 113-0033, Japan
***College of Veterinary Medicine·Research Institute of Veterinary Medicine, Chungnam National University, Daejeon 305-764, Korea
(Accepted: September 29, 2014)
Abstract : This case study describes the magnetic resonance characteristics of brain infarction in three dogs. Locations of the brain infarcts were cerebella, thalamus, and multifocal. The infarcts were sharply demarcated from adjacent brain parenchyma, homogeneous, T1-hypointense, T2-hyperintense with/without contrast enhancement, and minimal or no mass effect. Diffusion-weighted imaging (DWI) sequences were available in a dog and the infarcts were hyperintense on DWI and were hypointense on the apparent diffusion coefficient map.
Key words : brain infarction, DWI, ischemia, MRI, dog.
Introduction
Stroke or cerebrovascular accident is defined as a sudden onset of non-progressive focal neurological signs secondary to cerebrovascular disease. Stroke include rupture of a blood vessel causing hemorrhagic stroke and occlusion of the lumen of a vessel causing ischemic stroke or infarction depending on the severity of the ischemic event (1). Strokes are being recognized with greater frequency in veterinary medicine since magnetic resonance imaging (MRI) has become readily available (3). Introduction of functional MRI including diffusion-weighted imaging (DWI) improves the sensitivity and specificity for the diagnosis of acute brain inf- arction, compare with that of conventional MRI (7). However, only several reports describe the use of these neuroimaging techniques in animals with brain infarction (2,4,7).
This report describes the MRI characteristics suspected ischemic brain infarction in three dogs.
Case
Three dogs with diagnosed brain infarction by conven- tional and functional MRI were included in this study. Sig- nalment, clinical signs, and prognosis are summarized in Table 1. Breeds identified included two pure breeds (one each of Maltese and Pomeranian) and one mixed breed dog.
The dogs ranged in age from 9 to 13 years. All of three dogs were spayed female. The presenting complaints included acute onset of seizure (Dog 1 and Dog 3), ataxia (Dog 3),
nystagmus (Dog 1), spasticity of the forelimbs (Dog 2), and cervical tonic extension (Dog 2).
MRI was performed within 36 hours of onset of clinical signs using a 0.3T (Magfinder2, AILab, South Korea) or 1.5T (Magnetom Essenza, Siemens, Germany). Transeverse, sagittal, and dorsal plane images and a minimum of T2- weighted (T2WI) and non-contrast T1-weighted images (T1WI) and fluid-attenuated inversion recovery (FLAIR) were obtained. In addition, images obtained by means of post-contrast (IV injection of 0.1 mmol of gadodiamide/kg) T1WI and DWI were analyzed when available. DWI using an echo-planar technique with a b value of 800 were obtained when available. Apparent diffusion coefficient (ADC) maps were calculated from the DWI.
Infarction location, type, and vascular territory involved are summarized in Table 2. All infarcts were territorial. Loca- tion of the brain infarcts was cerebella (3 dogs), thalamus (1 dog, Fig 1), and multifocal (1 dog, Fig 2). The MRI findings are summarized in Table 3. The infarcts were sharply demar- cated from adjacent brain parenchyma, homogeneous, hy- pointense on T1WI, hyperintense on T2WI, and minimal or no mass effect in all of three dogs. Contrast study was per- formed in Dog 1 and Dog 3. The lesion did not enhance after contrast material administration in Dog 1. However, postcon- trast T1WI revealed scant uptake with contrast mainly the periphery of the lesion in Dog 3 (Fig 3). The lesion was hyper- intense on DWI and hypointense on the ADC map (Fig 4).
Dog 1 initially improved but deteriorated rapidly, and the patient died shortly afterwards. Dog 2 did not respond to a medical therapy for brain infarction and died 2 days after onset of clinical signs. In Dog 3, the neurologic deficits par- tially resolved by 2 weeks after the onset of clinical signs.
1Corresponding author.
E-mail: lywon@cnu.ac.kr
458 Ki-Ja Lee, Young-Whan Kim, Sung-Jin Choi, Soo-Young Choi, In-Seong Jeong, Ho-Jung Choi and Young-Won Lee
During the subsequent 6 months, the patient was improved and mild ataxia remained.
Discussion
Brain infarction may be associated with disease of main arteries or disease affecting small, deeply penetrating arteries that result in territorial and lacunar infarcts, respectively (6).
The most common location of the territorial infarcts is the cerebellum in dogs (4,9). Telencephalone and thalamic/mid- brain infarcts are common whereas multifocal infarcts are rare (9). The results of the present study are comparable to the previous studies (4,9). Cerebella infarcts were detected in all
of three dogs in the present study. A previous study reported that there was an apparent bias toward lesions occurring within the left side of the cerebellum but the reason for this is unknown (9). In the present study, however, there were two lesions in the right cerebellar hemisphere or paravermis and only one in the left side. Further studies are needed to deter- mine the affected side in patients with cerebellar infarction.
The MRI appearance of the lesions in this study was simi- lar to that reported for brain infarction of dogs (4,7,9). Brain infarcts confine to gray matter, but occasional white matter involvement with severe changes of gray matter. Ischemic inf- arcts are sharply demarcated lesions, which are homogeneous and hyperintense on T2WI and FLAIR images. Infarcts are often wedge shaped or roughly rectangular in shape with minimal or no mass effect (4,9). A minimal mass effect was seen with cerebral infarction in Dog 2 but was not seen with cerebellar infarction in any of the patients reported here. A mass effect usually develops 3-5 days after infarction because of vasogenic edema (8).
Contrast enhancement was seen in cerebellar infarction in Dog 3. It was faint and peripheral in location. A similar pat- tern of mild peripheral enhancement was seen in previously reported cerebellar infarction (2,9). The contrast enhancement is due to leakage of contrast medium through the damaged blood-brain barrier (8). Depending on time of brain infarc- tion to imaging, the degree and pattern of enhancement vary and are dependent on the severity of concurrent vasogenic edema and mass effect (8).
DWI is valuable in the investigation of suspect stroke in humans as it has been more sensitive than conventional MRI for detection of ischemic lesions (5). In addition, DWI per- mits detection of hyperacute stroke and differentiation from mimic stroke (5,11). The characteristics of ischemic infarc- tion is hyperintense on DWI and low intensity on ADC Table 1. Signalment, clinical signs, and prognosis in three dogs with brain infarction
No. Breed Age (y) Sex Clinical signs Prognosis
1 Mongrel 10 FS Acute tonic seizure, nystagmus Died (6 days)
2 Maltese 13 FS Spasticity of the forelimbs, cervical tonic extension Died (2 days)
3 Pomeranian 9 FS Acute seizure, ataxia Alive (6 months)
Table 2. Infarct location, type, and vascular territory involved in three dogs
No. Location Type Vascular territory
1 Left thalamus Right cerebellum Territorial Proximal perforating a. arising from the caudal communicating a. & rostral cerebella a.
2 Cerebrum (multifocal) Right cerebellum Territorial Middle cerebral a. & rostral cerebella a.
3 Left cerebellum Territorial Rostral cerebella a.
Table 3. Magnetic resonance characteristics of ischemic brain infarction in three dogs
No. Appearance Signal intensity Contrast enhancement Mass effect
1 sharp demarcation homogenous T1-hypointense
T2-hyperintense no no
2 sharp demarcation homogenous T1-hypointense
T2-hyperintense - slightly (cerebrum)
no (cerebellum) 3 sharp demarcation homogenous T1-hypointense
T2-hyperintense yes no
Fig 1. Transverse T2-weighted spin-echo (A), T2-FLAIR (B), and non- (C) and post-contrast (D) T1-weighted images at the level of the thalamus. The lesion is well demarcated and is T2- hyperintense to adjacent parenchyma (A and B) and T1- hypointense (C) with no contrast enhancement (D).
Magnetic Resonance Characteristics of Ischemic Brain Infarction in Three Dogs 459
maps, as observed in Dog 3 with presumptive infarction that were imaged within 3 days of the onset of clinical signs in this study. This pattern persists for the first 4 days after and ADC values typically change from low intensity to high after 7-10 days (9). For this change, the DWI allows discrimina- tion of acute versus chronic lesions (9,10). High signal inten- sity on DWI and low ADC despite having high sensitivity and specificity for the diagnosis of acute infarction has been reported in some patients to have false positive and negative (12). A similar pattern has been seen in patients with hemor-
rhage, abscess, and lymphoma in human (12). These condi- tions can be differentiated from acute infarction on the basis of history and characteristics on T2WI and post-contrast T1WI.
In summary, the MRI of canine brain infarction appears characteristic and similar to that previously reported in humans and dogs. They occur most commonly in cerebel- lum supplied by the rostral cerebellar artery. DWI may be useful to provide support for the diagnosis of acute brain inf- arction.
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Fig 3. Transverse T2-weighted spin-echo (A), T2-FLAIR (B), and non- (C) and post-contrast (D) T1-weighted images at the level of the rostral cerebellum. The lesion is well demarcated and is T2-hyperintense to adjacent parenchyma (A and B) and T1- hypointense (C) with mild peripheral contrast enhancement (D).
Fig 4. Transverse DWI (b factor = 800 s/mm2) (A) and corre- sponding ADC map (B) of the rostral cerebellar lesion in Fig 3.
The lesion is hyperintense on DWI (A), but hypointense on the ADC map (B), confirming restricted water diffusion.
Fig 2. Transverse T2-weighted spin-echo (A), T2-FLAIR (B), and non-contrast (C) T1-weighted images at the level of the tympanic bulla.
460 Ki-Ja Lee, Young-Whan Kim, Sung-Jin Choi, Soo-Young Choi, In-Seong Jeong, Ho-Jung Choi and Young-Won Lee
12. Stadnik TW, Demaerel P, Luypaert RR, Chaskis C, Van Rompaey KL, Michotte A, Osteaux MJ. Imaging tutorial:
differential diagnosis of bright lesions on diffusion-weighted MR images. Radiographics 2003; 23: e7.
자기공명영상을 이용한 개의 허혈성 뇌경색의 진단 3례
이기자·김영환*·최성진**·최수영***·정인성*·최호정***·이영원***1
경북대학교 수의과대학, *로얄동물메디컬센터, **동경대학교 수의외과학실, ***충남대학교 수의과대학
요 약 : 뇌경색으로 진단한 소형견 3 마리의 자기공명영상 (MRI)을 평가하였다. 뇌경색은 소뇌, 시상, 혹은 다발성으 로 발생하였다. 뇌경색은 병변의 경계가 비교적 뚜렷하고, 균질하게 T1강조영상에서 저신호, T2강조영상에서 고신호를 나타내었다. 조영증강효과는 없거나, 병변의 주변부로 미약하게 조영증강효과가 나타나기도 했다. 확산강조영상 (DWI) 에서는 고신호로 나타나며 이 부위의 겉보기확산계수 (ADC)는 감소되었다.
주요어 : 뇌경색, 자기공명영상, 개, 확산강조영상
