CT and cerebral ischemic infarcts

Summary A total of 66 patients with supratentorial ischemic infarct underwent serial CT scans in order to study the relationship between CT images and clinical evolution of the infarct. Little information of prognostic value is given by CT in patients with slight neurological deficits, whereas it enables factors with a negative influence on the prognosis to be identified in patients with moderate to severe deficits.     

Detectability and detection rate of acute cerebral hemisphere infarcts on CT and diffusion-weighted MRI

Our purpose was to compare the detectability and detection rate of acute ischaemic cerebral hemisphere infarcts on CT and diffusion-weighted MRI (DWI). We investigated 32 consecutive patients with acute hemisphere stroke with unenhanced CT and DWI within 6 h of stroke onset. The interval between CT and DWI ranged from 15 to 180 min (mean 60 min). Infarct detectability on CT and DWI was determined by comparing the initial CT, DWI and later reference images in a consensus reading of five independent examiners. The “true” detection rate was assessed by analysing all single readings. Two patients had intracerebral haematomas on DWI and CT and were excluded. There were 27 patients with ischaemic infarcts; all were visible on DWI and proven by follow-up. DWI was negative in three patients without a final diagnosis of infarct (100 % sensitivity, 100 % specificity, χ² = 30, P < 0.0001). Ischaemic infarcts were visible on 15 and not seen on 12 CT studies (55 % sensitivity, 100 %specificity, χ² = 1.48, P = 0.224). With regard to the single readings (30 examinations × 5 examiners = 150 readings), 63 CT readings were true positive and 72 false negative (sensitivity 47 %, specificity 86 %, χ² = 2.88, P = 0.089). Of the DWI readings 128 were true positive and 7 false negative (sensitivity 95 %, specificity 87 %, χ² = 70.67, P < 0.0001). Interobserver agreement was substantial for CT (ϰ = 0.72, 95 % confidence interval, 0.6–0.84) and DWI (ϰ = 0.82, 95 % confidence interval, 0.46–1). Taken together, detectability and detection rate of acute (< 6 h) hemisphere infarcts are significantly higher with DWI than with CT. Received: 14 December 1999/Accepted: 15 February 2000     

Transient disappearance of cerebral infarcts on CT scan,the so-called fogging effect

Summary The fogging effect, whereby initially hypodense infarcts become isodense during the second and third week after the onset of stroke, was investigated in a prospective and consecutive series comprising 50 cases with completed stroke. CT scans were performed approximately 3 days, 10 days and 6 months after stroke. The fogging effect was found in 54% of cases. The hypodense areas reappeared on all scans at 6 months. Cerebral infarcts therefore may be overlooked or grossly underestimated if the scan is performed during the second and third week after stroke.     

CT fogging effect with ischemic cerebral infarcts

Summary Systematic CT studies on ten patients with persistent ischemic cerebral infarct revealed a constant phenomenon, the fogging effect. The hypodense infarct at the beginning will be isodense, or close to isodense, on the plain CT during the second or third weeks and at a later stage will be hypodense again. The fogging infarcted area shows homogeneous intensive contrast enhancement. Knowledge of the fogging effect is important for correct interpretation of the CT image and the indication for contrast medium CT. CT without contrast medium may lead to misinterpretation during the second and third weeks after the onset of cerebral infarction.Presented at the Annual Meeting of the German Society of Neurology, Berlin, 4–6 October 1978     

X-ray computed tomography (CT) study of small,deep and recent infarcts (SDRIs) of the cerebral hemispheres in adults

Summary The evolution of CT signs of small, deep infarcts of the cerebral hemispheres in thirty adults, in the first five weeks, has been retrospectively studied. The relevant literature has been reviewed and an attempt has been made to present a synthesis, accompanied by a commentary. It is impossible now to give the frequency of each type of evolution, but the main data are as follows: 1. The shortest delay of visibility of an hypodense area is about 17 to 19h, but at 27 h the densities may still be normal. 2. The evolution of the hypodense area is also variable: after a minimum attenuation is reached-at approximately 72 h-there is a risk of fogging effect, which reduces the visibility of ischemic lesions; it could be seen from the end of the 1st week to the beginning of the 4th, but its frequency and its duration have yet to be better determined. 3. In our series, contrast enhancement has been found in the gray matter of the basal ganglia between the 8th and the 22nd days-but according to some observations recorded in the literature, it may be found from the second to the twenty sixth day-and there was no obvious contrast enhancement in the white matter. The significance of the evolving CT signs is discussed in connection with the clinical applications, principally in the management of these patients, and with the attempts to correlate the clinical and CT findings.     

The place of digital intravenous angiography in cerebral infarcts

Summary The authors describe their technique of intravenous digital substraction angiography (IVDSA) and discuss the results in cerebral infarcts. IVDSA is a good first stage examination for the recognition of stenosis or occlusion of cervical vessels to the brain, as it is an only marginally invasive and easy technique. It is, however, good neither for the study of focal cervical not of intracranial areas.     

Morphology of cerebral lesions in children with congenital hemiplegia

Summary This study has analysed the results of CT scans of the brains in children with congenital hemiplegia. The material consists of 111 out of a total of 151 children with this cerebral palsy syndrome in a population-based series. We have classified the morphological findings in five groups. The groups are designed to reflect the phase of maturation of the brain when the insult happened. The groups are: 1. Maldevelopment, 2. Periventricular atrophy, 3. Cortical-/subcortical atrophy, 4. Miscellaneous, 5. Normal. In contrast to previous reports we found a high proportion (17%) with maldevelopment. However the dominating morphological pattern was periventricular atrophy, consistent with a hypoxic-ischemic insult to the immature brain, seen in 42%. Cortical and/or subcortical atrophy was found in 12%. Three children (3%) presented with morphological patterns not possible to classify. The group with no pathology according to CT was 26%.     

Improved CT diagnosis of acute middle cerebral artery territory infarcts with density-difference analysis

A new postprocessing method is described for CT detection of acute middle cerebral artery (MCA) territory infarcts by histograph analysis of density values. The density values in each CT slice were histographically recorded for each hemisphere. A density-difference diagram was calculated by digital subtraction of the histogram of the left hemisphere from that of the right. Pixels within the highest density-difference ranges were highlighted. To investigate the value of this method CT studies of 30 patients with acute MCA territory infarcts and of 15 normal CT studies were analysed by two radiologists and neurosurgeons. CT images with and without postprocessing were assessed for the presence, site and size of infarcts. Follow-up CT was used as control. With density-difference analysis (DDA) the detection rate for infarcts increased significantly (96 % compared to 61 %). In no case was a correct diagnosis made on the unpostprocessed images falsely revised with DDA. All normal CT studies were detected correctly using DDA. Received: 16 October 1995 Accepted: 20 March 1996     

Analysis of IMP-SPECT in cerebral infarcts

We performed single photon emission computed tomography withN-isopropyl [¹²³I]-p-iodoamphetamine in 22 normal volunteers (mean age, 68.3±9.5 years) and 190 patients with unilateral cerebral infarcts (66.1±11.4 years). We then compared visual and semiquentitative assessment of the left/right ratio of the early images. Cerebral blood flow in the patients with cerebral infarcts was compared with data from normal volunteers. An abnormal left/right ratio was recognized in 110 of 136 (81%) patients in whom X-ray computed tomography (CT) showed an abnormality, while visual inspection revealed abnormalities in only 99 (73%). In 54 patients no abnormality on CT, an abnormal left/right ratio was found in 28 (52%), and visual abnormalities in only 9 (17%). Altogether, the left/right ratio was abnormal in 138 of 190 (73%) patients, and abnormalities were detected visually in 108 (57%). Of 95 patients, 56 (59%) showed markedly larger lesions using the left/right ratio method than with the visual method.     

Haemodynamics and oxygen metabolism in patients after reversible ischaemic attack or minor ischaemic stroke assessed with positron emission tomography

Summary Regional cerebral blood flow (CBF), blood volume (CBV) and oxygen metabolic rate (CMRO2) were evaluated and compared among normals, patients with recent reversible ischaemic attacks (RIAs) and patients with chronic minor infarction using positron emission tomography. Average CBF together with CMRO2 significantly decreased in the infarction group in the middle cerebral artery territory of the affected hemisphere while the mean values for RIAs were intermediate between the other two groups. CBV also reduced, however it was more preserved compared to flow as seen in decreased CBF/CBV values. Significant interhemispheric difference was found in CBF/CBV ratio, but it did not clearly correlate with OEF changes. Higher OEF was noted only in the restricted brain regions of RIAs where CBF showed large hemispheric asymmetry. However, in other regions, the coupled decline of blood flow and metabolism was found which suggests tissue damage or neuronal cell loss in the brain with previous RIA symptoms.     

MRI of acute cerebral infarcts: increased contrast enhancement with continuous infusion of gadolinium

We compared contrast enhancement on T1-weighted MRI of acute cerebral infarcts after conventional bolus administration and continuous infusion of gadolinium. We examined 12 patients with a history of acute stroke with contrast-enhanced MRI once a week for a 1 month. Only ischaemic lesions were investigated after cerebral haemorrhage had been excluded by CT. Each MRI study included T2- and proton density-weighted sequences for determination of the size and site of the infarct, immediate postinjection T1-weighted imaging after bolus administration of 0.1 mmol/kg gadolinium-DPTA and delayed T1-weighted imaging after additional continuous infusion of 0.1 mmol/kg over 2 h. A total of 42 MRI studies was performed. In the first week after the onset of stroke, most infarcts (8 of 10) did not enhance after bolus administration, whereas all showed distinct contrast enhancement after the infusion. In the following weeks all but two infarcts showed contrast enhancement after bolus administration; after continuous infusion contrast enhancement could be seen in all cases. While contrast enhancement after bolus administration showed the typical gyriform pattern, enhanced areas were more extensive after the infusion and usually covered the entire infarcted area shown on T2- and proton density-weighted images. We presume that the disturbed blood-brain barrier in ischaemic areas favours delivery of contrast medium to the infarcted tissue if it is offered continuously so that a steady state can develop. Received: 8 April 1998 Accepted: 1 September 1998     

SPET brain imaging with 201 diethyldithiocarbamate in acute ischaemic stroke

Thirty-five patients with acute ischaemic stroke were studied within 24 h after hospital admission with thallium 201 diethyldithiocarbamate single photon emission tomography (²⁰¹TI-DDC SPET) and X-ray computed tomography (CT).²⁰¹TI-DDC is a non-redistributing agent that allows postponed imaging after early administration and early therapeutic intervention. In 16 patients both investigations were performed within 24 h after stroke onset. The sensitivity of SPET was 94% and of CT 81 % in the first 24 h, when hypodensity and obliteration of sulci were used as CT reading criteria. When only hypodensity was used as a criterion, the sensitivity of CT was 50% in this group. Sensitivity of CT compared with SPET became increasingly better in patients with older infarcts (1–18 days). In two-thirds of patients, the lesion demonstrated on SPET was larger than that on CT, and this was especially so with older infarcts. Crossed cerebellar diaschisis occurred in 69% of patients. The high sensitivity of²⁰¹TI-DDC SPET in the first 24 h after ischaemic stroke and the favourable properties of this radiopharmaceutical make it a method of interest in the assessment of initial perfusion defects in early experimental stroke therapies.     

The characteristics of cerebral meningiomas and surrounding tissues on dynamic CT

Summary Dynamic CT was utilized to evaluate 11 patients with histologically benign meningiomas. While it was found that all demonstrated macroscopic neovascularity, subtle differences in the dynamic perfusion curves were identified both between different meningiomas and from region to region within the same tumor. Other than basic anatomic differences, these changes may reflect intratumoral ischemia and hypothetically herald cystic/necrotic alteration within the neoplasm. The dynamic calculations over the surrounding brain showed areas of gross hyper- and hypoperfused cerebral cortex, and hypoperfused white matter in regions of peritumoral edema. These latter findings are of uncertain clinical importance. The dynamic examination also confirmed cases of dural venous sinus invasion and calvarial permeation by tumor. In addition, the dynamic series showed macroscopic neovascularity in one case with a completely negative selective cerebral arteriogram. It is felt that certain cases which have previously been evaluated by static CT may benefit from further study utilizing the dynamic method.     

Neoplastic encephalopathy: dynamic CT of cerebral gliomata

Summary Intravenous contrast enhanced dynamic computed tomography of cerebral gliomata reveals a spectrum of patterns which reflect different degrees of neovascularity as well as a variable breakdown in the blood-tumor-barrier both intratumorally as well as between individual tumors. Phenomena not generally associated with gliomas including intrinsic neoplastic and peripheral cerebral hypoperfusion, hyperperfusion, and indications of vascular stealing are also demonstrated with this technique which conceivably explain and are partially responsible for certain aspects of the encephalopathy accompanying cerebral neoplasia. A comparison of the dynamic sequences with conventional selective cerebral angiography further indicates that the more contrast-sensitive dynamic method is potentially superior in the detection of subtle neovascularity.     

伴皮质下梗死和白质脑病常染色体显性遗传性脑动脉病CT平扫特点

目的：探讨伴皮质下梗死和白质脑病的常染色体显性遗传性脑动脉病（CADASIL）CT平扫特点。方法：对8例经临床、MRI、病理学及基因检查确诊为CADASIL患者的CT平扫资料进行回顾性分析。结果：CADASIL患者脑CT平扫特点主要表现为颞极、额叶前部白质疏松,可伴有腔隙性梗死灶,随年龄增长上述病灶逐渐加重。结论：CADASIL病例CT平扫存在特征性的脑白质病变,CT对该病的筛选有重要作用。     

CT analysis of the upper end of the femur: The asterisk sign and ischaemic bone necrosis of the femoral head

In computed tomography (CT) of the head of the femur, a star-shaped structure can be seen which we refer to as theasterisk orasterisk sign. The asterisk is formed by thickened weight-bearing bone trabeculae. It can be shown by CT that the asterisk exhibits a characteristic change in ischaemic bone necrosis of the femoral head, even when the disease is in an early stage. CT of the hip joint is therefore an important examination for early diagnosis of ischaemic disease of the femoral head.     

Serial CT and MRI of ischaemic cerebral infarcts: frequency and clinical impact of haemorrhagic transformation

The frequency, predisposing factors and clinical consequences of haemorrhagic infarcts and damaged blood-brain barrier as shown by contrast enhancement (CE) in ischaemic cerebral infarcts are controversial. We prospectively compared the sensitivity of CT and MRI to haemorrhagic transformation (HT) and CE. We also wished to investigate the clinical significance of HT and factors possibly associated with it. We studied 36 patients with acute ischaemic infarcts in the middle cerebral artery territory during the first 2 weeks after the ictus. After CT and rating of the neurological deficit on admission, serial examinations with clinical neuromonitoring, contrast-enhanced CT and MRI were done on the same day. The occurrence and severity of HT were correlated with CE, stroke mechanism, infarct size, development of neurological deficits and antithrombotic treatment. The frequency of HT detected by MRI was 80 %. CE usually preceded HT or was seen simultaneously. MRI had a higher sensitivity than CT to HT and CE. Severity of HT was positively correlated with infarct size (P < 0.01). HT had no influence on patient's neurological status. Neither the type of antithrombotic treatment nor the stroke mechanism was associated with the severity of HT. No parenchymal haemorrhage occurred. Received: 10 November 1998 Accepted: 29 July 1999     

MRI assessment of cerebral blood volume in patients with brain infarcts

MRI perfusion studies have focussed mainly on acute ischaemia and characterisation in ischaemia. Our purpose was to analyse regional brain haemodynamic information in acute, subacute, and chronic ischaemia. We performed 16 examinations of 11 patients on a 1.5 T MR images. Conventional and dynamic contrast-enhanced imaging were employed in all examinations. For the dynamic susceptibility sequences, a bolus (0.2 mmol/kg) of gadopentetate dimeglumine was injected. Reconstructed regional relative cerebral blood volume (rCBV) maps, bolus maps, and conventional images were analysed by consensus reading. In all examinations decreases in rCBV were observed in the lesions. The distribution of regional rCBV in lesions was heterogeneous. The rCBV of the periphery of the lesions was higher than that at their center. There was a correlation between the time since onset and abnormalities on the rCBV map and T2-weighted images (T2WI). In the early stage of acute stroke, the abnormalities tended to be larger on the rCBV than on T2WI. Many patterns of bolus passage were observed in ischaemic regions. rCBV maps provide additional haemodynamic information in patients with brain infarcts. Received: 15 September 1997 Accepted: 22 December 1997     

Assessment of pathophysiology of stroke by positron emission tomography

In stroke patients, multitracer positron emission tomography (PET) permits the assessment of acute changes in regional cerebral blood flow (rCBF), blood volume (rCBV), oxygen consumption (rCMRO₂) and glucose metabolism (rCMR_gl), which are the initial steps in the complex molecular and biochemical process leading to ischaemic cell damage. While early infarcts exhibit low flow and oxygen consumption, increased oxygen extraction fraction (OEF) due to preserved metabolism at reduced flow suggests viability of tissue. However, most initially viable tissue will be metabolically deranged and will become necrotic in the further course; only in a few instances do these tissue compartments recover to normal function. Increased glucose uptake at reduced oxygen supply induces non-oxidative glycolysis with noxious lactacidosis, whereas hyperperfusion beyond the metabolic demand is of controversial effect. In subacute or chronic states after ischaemia reduced flow can be compensated by increased blood volume; when perfusional reserve is exhausted, oxygen extraction increases. Such findings may guide therapeutic decisions and predict the severity of permanent deficits. Functional deactivation of tissue remote from the lesion is found regularly as a sign of damaged connecting pathways. Flow and metabolic studies during the performance of specific tasks help to detect alternative functional loops and may yield prognostic information. Repeat studies in the course of stroke are employed for the evaluation of therapeutic strategies targeted to improve reperfusion or to effect metabolic or biochemical alterations. In the future PET may gain additional clinical importance when patients are selected for elective treatment according to the prevailing pathophysiological pattern. Correspondence to: W.-D. Heiss