Increased signal in the subarachnoid space on fluid-attenuated inversion recovery imaging associated with the clearance dynamics of gadolinium chelate: a potential diagnostic pitfall

Pseudosubarachnoid Hemorrhage on MRI: A potential pitfall

Fluid attenuated inversion recovery (FLAIR) is one of the most effective magnetic resonance imaging (MRI) sequences in the diagnosis of subarachnoid hemorrhage (SAH). However, sometimes false positive or false negative results can occur. One of the reasons that can lead to erroneous interpretation is artifacts. Especially when metallic artifact occurs, hyperintensity may be observed in the subarachnoid space, similar to SAH. Although FLAIR hyperintensities in the sulci can be detected in many serious diseases, they are not always pathological. Artifact related hyperintensities, especially in cases with severe headache, may be mistakenly evaluated as SAH by a clinician or radiologist who is not well-experienced in MRI. However, it is extremely important to recognise these artifact related hyperintensities, to make a correct diagnosis and to prevent unnecessary interventions. In order to achieve this, the evaluation of all radiological images, especially SWI and GRE, is critical. Both radiologists and clinicians evaluating neuroradiological examinations should be knowledgeable about this subject and show maximum attention. In this report, we present the radiological images of 4 cases of pseudosubarachnoid hemorrhage, one of which was caused by conductive EEG gel and the other three due to braces artifacts, who were admitted to the hospital with headache.

Rare pitfall in the magnetic resonance imaging of status epilepticus

Brain MRI in Status Epilepticus (SE) is often helpful in diagnosis, lateralization and localization of the seizure focus. MRI changes in SE include predominantly ipsilateral diffusion weighted imaging (DWI) changes in the hippocampus and pulvinar or similar changes involving basal ganglia, thalamus, cerebellum, brain stem and external capsule (Chatzikonstantinou et al., 2011 [1]). These changes are thought to be due to transient vasogenic and cytotoxic edema due to either transient damage or breakdown of blood brain barrier, proportional to the frequency and duration of the epileptic activity (Amato et al., 2001 [2]). Such changes may also be reflected on T2- weighted and T2-Fluid-Attenuated Inversion Recovery (FLAIR) sequences of MRI. Herein, we present a case of a transient FLAIR cerebrospinal fluid (CSF) hyperintensity on the second MRI brain in a patient with focal status epilepticus. This imaging finding led to diagnostic confusion and was initially thought to represent subarachnoid hemorrhage. However, lumbar puncture, brain computed tomography (CT), and a follow-up brain MRI ruled out that possibility and other CSF pathologies. We concluded that the transient FLAIR changes in the second brain MRI were related to a rare imaging pitfall caused by Gadolinium enhancement of CSF on the FLAIR sequence, popularly referred to as hyperintense acute reperfusion marker (HARM).

Ipsilateral blooming of microbleeds after Hyperintense Acute Reperfusion Marker sign in an ischemic Stroke patient, a case report

Background

Hyperintense Acute Reperfusion Marker (HARM) is a hyperintense subarachnoid signal on FLAIR MRI sequence caused by gadolinium contrast leakage into the subpial space. While, on FLAIR, HARM may mimic subarachnoid hemorrhage, it is differentiated from it on computed tomography (CT) and SWAN MRI sequences. Cerebral microbleeds are black, rounded spots on SWAN caused by blood-products deposition following red blood cell leakage from small cerebral vessels brain. Both microbleeds and HARM carry important prognostic implication as they are associated with blood-brain barrier disruption and an increased risk of intracerebral hemorrhage.

Case presentation

A 79-year-old man presented with aphasia and right hemiparesis due to ischemic stroke with left middle cerebral artery occlusion. Admission NIHSS score was 7, and he was successfully treated by intravenous thrombolysis and mechanical thrombectomy. On day 1, his clinical condition worsened, and he had an urgent gadolinium-enhanced MRI. There was no evidence of early recurrence, nor of hemorrhage on SWAN or on FLAIR. Left middle cerebral artery was permeable. The patient was anticoagulated for newly diagnosed atrial fibrillation, and a second MRI following a generalized tonic-clonic seizure showed multiple left hemispheric diffusion-weighted imaging (DWI) hyperintense spots and a left hemispheric sub-arachnoid hyperintensity on FLAIR, compatible with a subarachnoid hemorrhage. This diagnosis was excluded by SWAN MRI sequence and a normal cerebral CT the same day. The diagnosis of HARM was retained. At day 9, patient’s condition improved, and a control MRI did not show evidence of HARM. However, numerous microbleeds were detected in the left hemisphere only (ipsilateral with HARM and stroke).

Conclusions

This case highlights first of all the importance of differentiating HARM and subarachnoid hemorrhage, especially in an anticoagulated patient with clinical aggravation. Secondly, it is crucial to identify microbleeds and understand their pathophysiology, as they are associated with higher risk of hemorrhage and stroke recurrence in ischemic stroke patients. Finally, the mono-hemispheric appearance of microbleeds in this case suggests for the first time that, in some acute ischemic stroke patients, a relationship between HARM and cerebral microbleeds may exist.

Small Brain Lesion Enhancement and Gadolinium Deposition in the Rat Brain: Comparison Between Gadopiclenol and Gadobenate Dimeglumine

OBJECTIVES

The aim of the set of studies was to compare gadopiclenol, a new high relaxivity gadolinium (Gd)-based contrast agent (GBCA) to gadobenate dimeglumine in terms of small brain lesion enhancement and Gd retention, including T1 enhancement in the cerebellum.

MATERIALS AND METHODS

In a first study, T1 enhancement at 0.1 mmol/kg body weight (bw) of gadopiclenol or gadobenate dimeglumine was evaluated in a small brain lesions rat model at 2.35 T. The 2 GBCAs were injected in an alternated and cross-over manner separated by an interval of 4.4 ± 1.0 hours (minimum, 3.5 hours; maximum, 6.1 hours; n = 6). In a second study, the passage of the GBCAs into cerebrospinal fluid (CSF) was evaluated by measuring the fourth ventricle T1 enhancement in healthy rats at 4.7 T over 23 minutes after a single intravenous (IV) injection of 1.2 mmol/kg bw of gadopiclenol or gadobenate dimeglumine (n = 6/group). In a third study, Gd retention at 1 month was evaluated in healthy rats who had received 20 IV injections of 1 of the 2 GBCAs (0.6 mmol/kg bw) or a similar volume of saline (n = 10/group) over 5 weeks. T1 enhancement of the deep cerebellar nuclei (DCN) was assessed by T1-weighted magnetic resonance imaging at 2.35 T, performed before the injection and thereafter once a week up to 1 month after the last injection. Elemental Gd levels in central nervous system structures, in muscle and in plasma were determined by inductively coupled plasma mass spectrometry (ICP-MS) 1 month after the last injection.

RESULTS

The first study in a small brain lesion rat model showed a ≈2-fold higher number of enhanced voxels in lesions with gadopiclenol compared with gadobenate dimeglumine. T1 enhancement of the fourth ventricle was observed in the first minutes after a single IV injection of gadopiclenol or gadobenate dimeglumine (study 2), resulting, in the case of gadopiclenol, in transient enhancement during the injection period of the repeated administrations study (study 3). In terms of Gd retention, T1 enhancement of the DCN was noted in the gadobenate dimeglumine group during the month after the injection period. No such enhancement of the DCN was observed in the gadopiclenol group. Gadolinium concentrations 1 month after the injection period in the gadopiclenol group were slightly increased in plasma and lower by a factor of 2 to 3 in the CNS structures and muscles, compared with gadobenate dimeglumine.

CONCLUSIONS

In the small brain lesion rat model, gadopiclenol provides significantly higher enhancement of brain lesions compared with gadobentate dimeglumine at the same dose. After repeated IV injections, as expected for a macrocyclic GBCA, Gd retention is minimalized in the case of gadopiclenol compared with gadobenate dimeglumine, resulting in no T1 hypersignal in the DCN.

GLOS and HARM in patients with transient neurovascular symptoms with and without ischemic infarction

BACKGROUND AND PURPOSE

Gadolinium leakage in ocular structures (GLOS) on fluid attenuated inversion recovery images (FLAIR) is a novel imaging marker in acute ischemic stroke and other neurological disorders.

METHODS

In patients with transient neurovascular symptoms who underwent repeated MRI with intravenous contrast agent administration, the presence of acute ischemic lesions on diffusion-weighted images (DWI) as well as the frequency and pattern of blood-brain barrier and blood-retina barrier impairment as demonstrated by the hyperintense acute reperfusion marker (HARM) and GLOS respectively on postcontrast FLAIR were evaluated.

RESULTS

Overall 28 patients with transient neurovascular symptoms (median age 70.5 years; 18 (64.3%) male) were included. Follow-up MRI was performed within 35 (IQR 21-47) hours after the initial MRI. On DWI, acute ischemic lesions were observed in 22 (78.6%). On contrast-enhanced FLAIR, GLOS was observed in 12 (42.9%) patients: in 1 (3.6%) only in the anterior chamber, and in 11 (39.3%) in the anterior chamber and vitreous body. HARM was observed in 3 (10.7%) patients. In one patient without ischemic lesion on DWI or HARM on FLAIR, GLOS was observed in the anterior chamber and vitreous body. Presence of GLOS was associated with higher age (p = 0.04) and detection of HARM (p = 0.03).

CONCLUSIONS

In patients with transient neurovascular symptoms, GLOS is a frequent finding and associated with HARM on contrast-enhanced FLAIR. As GLOS was observed in one patient without an ischemic lesion or HARM, it might be useful as an additional imaging marker.

Retention of Gadolinium in Brain Parenchyma: Pathways for Speciation, Access, and Distribution. A Critical Review

The unexpected appearance of T₁ hyperintensities, mostly in the dentate nucleus and the globus pallidus, during nonenhanced MRI was reported in 2014. This effect is associated with prior repeated administrations of gadolinium (Gd)‐based contrast agents (GBCAs) in patients with a functional blood–brain barrier (BBB). It is widely assumed that GBCAs do not cross the intact BBB, but the observation of these hypersignals raises questions regarding this assumption. This review critically discusses the mechanisms of Gd accumulation in the brain with regard to access pathways, Gd species, tissue distribution, and subcellular location. We propose the hypothesis that there is early access of Gd species to cerebrospinal fluid, followed by passive diffusion into the brain parenchyma close to the cerebral ventricles. When accessing areas rich in endogenous metals or phosphorus, the less kinetically stable GBCAs would dissociate, and Gd would bind to endogenous macromolecules, and/or precipitate within the brain tissue. It is also proposed that Gd species enter the brain parenchyma along penetrating cortical arteries in periarterial pial‐glial basement membranes and leave the brain along intramural peri‐arterial drainage (IPAD) pathways. Lastly, Gd/GBCAs may access the brain parenchyma directly from the blood through the BBB in the walls of capillaries. It is crucial to distinguish between the physiological distribution and drainage pathways for GBCAs and the possible dissociation of less thermodynamically/kinetically stable GBCAs that lead to long‐term Gd deposition in the brain.

Level of Evidence

5.

Technical Efficacy Stage

3.

Methodological Aspects for Preclinical Evaluation of Gadolinium Presence in Brain Tissue: Critical Appraisal and Suggestions for Harmonization-A Joint Initiative

Gadolinium (Gd)-based contrast agents (GBCAs) are pharmaceuticals that have been approved for 30 years and used daily in millions of patients worldwide. Their clinical benefits are indisputable. Recently, unexpected long-term presence of Gd in the brain has been reported by numerous retrospective clinical studies and confirmed in preclinical models particularly after linear GBCA (L-GBCA) compared with macrocyclic GBCA (M-GBCA). Even if no clinical consequences of Gd presence in brain tissue has been demonstrated so far, in-depth investigations on potential toxicological consequences and the fate of Gd in the body remain crucial to potentially adapt the clinical use of GBCAs, as done during the nephrogenic systemic fibrosis crisis. Preclinical models are instrumental in the understanding of the mechanism of action as well as the potential safety consequences. However, such models may be associated with risks of biases, often related to the protocol design. Selection of adequate terminology is also crucial. This review of the literature intends to summarize and critically discuss the main methodological aspects for accurate design and translational character of preclinical studies.

HARMless: Transient Cortical and Sulcal Hyperintensity on Gadolinium-Enhanced FLAIR after Elective Endovascular Coiling of Intracranial Aneurysms

BACKGROUND AND PURPOSE

Cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR has been increasingly recognized after iodinated contrast medium exposure during angiographic procedures. The goal of this study was to assess the relationship of cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR against various variables in patients following elective endovascular treatment of intracranial aneurysms.

MATERIALS AND METHODS

We performed a retrospective review of 58 patients with 62 MR imaging studies performed within 72 hours following endovascular treatment of intracranial aneurysms. Patient demographics, aneurysm location, and vascular territory distribution of cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR were documented. Analysis of cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR with iodinated contrast medium volume, procedural duration, number of angiographic runs, and DWI lesions was performed.

RESULTS

Cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR was found in 32/62 (51.61%) post-endovascular treatment MR imaging studies, with complete resolution of findings in all patients on the available follow-up studies (27/27). Angiographic iodinated contrast medium injection and arterial anatomy matched the vascular distribution of cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR. No significant association was found between cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR with iodinated contrast medium volume (P = .56 value) and the presence of DWI lesions (P = .68). However, a significant association was found with procedural time (P = .001) and the number of angiographic runs (P = .019). No adverse clinical outcomes were documented.

CONCLUSIONS

Cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR is a transient observation in the arterial territory exposed to iodinated contrast medium during endovascular treatment of intracranial aneurysms. Cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR is significantly associated with procedural time, and the frequency of angiographic runs suggesting a potential technical influence on the breakdown of the BBB, but no reported adverse clinical outcome or association with both iodinated contrast medium volume and DWI lesions was found. Recognition of cortical and sulcal hyperintensity on gadolinium-enhanced FLAIR as a benign incidental finding is vital to avoid unnecessary investigation.

The Cerebrovascular-Chronic Kidney Disease Connection: Perspectives and Mechanisms

Chronic kidney disease (CKD) is an independent risk factor for the development of cerebrovascular disease, particularly small vessel disease which can manifest in a variety of phenotypes ranging from lacunes to microbleeds. Small vessel disease likely contributes to cognitive dysfunction in the CKD population. Non-traditional risk factors for vascular injury in uremia include loss of calcification inhibitors, hyperphosphatemia, increased blood pressure variability, elastinolysis, platelet dysfunction, and chronic inflammation. In this review, we discuss the putative pathways by which these mechanisms may promote cerebrovascular disease and thus increase risk of future stroke in CKD patients.

Hyperintense Acute Reperfusion Marker on FLAIR in Posterior Circulation Infarction

Purpose

In the present study, we aimed to investigate the frequency of blood brain barrier injury in posterior circulation infarction as demonstrated by the hyperintense acute reperfusion marker (HARM) on fluid attenuated inversion recovery images (FLAIR).

Methods

From a MRI report database we identified patients with posterior circulation infarction who underwent MRI, including perfusion-weighted images (PWI), within 12 hours after onset and follow-up MRI within 24 hours and analyzed diffusion-weighted images (DWI), PWI, FLAIR, and MR angiography (MRA). On FLAIR images, the presence of HARM was noted by using pre-specified criteria (focal enhancement in the subarachnoid space and/or the ventricles).

Results

Overall 16 patients (median age of patients 68.5 (IQR 55.5–82.75) years) with posterior circulation infarction were included. Of these, 13 (81.3%) demonstrated PCA occlusion, and 3 (18.7%) patients BA occlusion on MRA. Initial DWI demonstrated ischemic lesions in the thalamus (68.8%), splenium (18.8%), hippocampus (75%), occipital lobe (81.3%), mesencephalon (18.8%), pons (18.8%), and cerebellum (50%). On follow-up MRA recanalization was noted in 10 (62.5%) patients. On follow-up FLAIR images, HARM was observed in 8 (50%) patients. In all of these, HARM was detected remote from the acute ischemic lesion. HARM was more frequently observed in patients with vessel recanalization (p = 0.04), minor infarction growth (p = 0.01), and smaller ischemic lesions on follow-up DWI (p = 0.05).

Conclusions

HARM is a frequent finding in posterior circulation infarction and associated with vessel recanalization, minor infarction growth as well as smaller infarction volumes in the course. Neuroradiologists should be cognizant of the fact that HARM may be present on short interval follow-up FLAIR images in patients with acute ischemic infarction who initially underwent MRI and received intravenous gadolinium-based contrast agents.

Importance of Contrast-Enhanced Fluid-Attenuated Inversion Recovery Magnetic Resonance Imaging in Various Intracranial Pathologic Conditions

Intracranial lesions may show contrast enhancement through various mechanisms that are closely associated with the disease process. The preferred magnetic resonance sequence in contrast imaging is T1-weighted imaging (T1WI) at most institutions. However, lesion enhancement is occasionally inconspicuous on T1WI. Although fluid-attenuated inversion recovery (FLAIR) sequences are commonly considered as T2-weighted imaging with dark cerebrospinal fluid, they also show mild T1-weighted contrast, which is responsible for the contrast enhancement. For several years, FLAIR imaging has been successfully incorporated as a routine sequence at our institution for contrast-enhanced (CE) brain imaging in detecting various intracranial diseases. In this pictorial essay, we describe and illustrate the diagnostic importance of CE-FLAIR imaging in various intracranial pathologic conditions.

Subarachnoid hemorrhage in ten questions

Traumatic subarachnoid hemorrhage (SAH) has an annual incidence of 9 per 100 000 people. It is a rare but serious event, with an estimated mortality rate of 40% within the first 48hours. In 85% of cases, it is due to rupture of an intracranial aneurysm. In the early phase, during the first 24hours, cerebral CT, combined with intracranial CT angiography is recommended to make a positive diagnosis of SAH, to identify the cause and to investigate for an intracranial aneurysm. Cerebral MRI may be proposed if the patient's clinical condition allows it. FLAIR imaging is more sensitive than CT to demonstrate a subarachnoid hemorrhage and offers greater degrees of sensitivity for the diagnosis of restricted subarachnoid hemorrhage in cortical sulcus. A lumbar puncture should be performed if these investigations are normal while clinical suspicion is high.

Differentiation of Leptomeningeal and Vascular Enhancement on Post-contrast FLAIR MRI Sequence: Role in Early Detection of Infectious Meningitis

OBJECTIVE

To qualitatively and quantitatively differentiate leptomeningeal and vascular enhancement on Post-contrast Fluid Attenuated Inversion Recovery (PCFLAIR) sequence compared to post-contrast T1-weighted (PCT1W) sequence with fat suppression (FS) and evaluate its role in early detection of infectious meningitis.

MATERIALS AND METHODS

Thirty-one patients with diagnosis of meningitis were evaluated with pre and post-contrast FLAIR and T1-weighted sequences with fat suppression (FS). Qualitative assessment was done by two observers for presence, absence or equivocal status of leptomeningeal enhancement. Further, quantitative estimation of single pixel signal intensities (SPSI) for meningeal and vascular enhancement was undertaken. A statistical comparison was performed using Kappa coefficient and t-test.

RESULTS

The overall qualitative accuracy was 90.3% for PCFLAIR compared to 54.8% for PCT1W with FS sequence. PCFLAIR was found to be 100% accurate in the detection of tubercular and pyogenic meningitis and 70% accurate in the detection of viral meningitis while PCT1W with FS sequence showed the corresponding accuracy to be 76.2% and 0% respectively. Both observers rated PCFLAIR images better than PCT1W with FS at detecting meningitis (p<0.05). The quantitative assessment revealed that the SPSI difference between the average meningeal and vascular enhancement on PCFLAIR was significantly greater than that on PCT1W with FS sequence (t= 6.31, p<0.01).

CONCLUSION

PCFLAIR sequence has insignificant component of vascular enhancement compared to meningeal enhancement. This makes meningeal inflammation easily discernable and aids in early detection of infectious meningitis.

Flat detector angio-CT following intra-arterial therapy of acute ischemic stroke: identification of hemorrhage and distinction from contrast accumulation due to blood-brain barrier disruption

BACKGROUND AND PURPOSE

Flat panel detector CT in the angiography suite may be valuable for the detection of intracranial hematomas; however, abnormal contrast enhancement frequently mimics hemorrhage. We aimed to assess the accuracy of flat panel detector CT in detecting/excluding intracranial bleeding after endovascular stroke therapy and whether it was able to reliably differentiate hemorrhage from early blood-brain barrier disruption.

MATERIALS AND METHODS

Seventy-three patients were included for retrospective evaluation following endovascular stroke therapy: 32 after stent-assisted thrombectomy, 14 after intra-arterial thrombolysis, and 27 after a combination of both. Flat panel CT images were assessed for image quality and the presence and type of intracranial hemorrhage and BBB disruption by 2 readers separately and in consensus. Follow-up by multisection head CT, serving as the reference standard, was evaluated by a single reader.

RESULTS

Conventional head CT revealed intracranial hematomas in 12 patients (8 subarachnoid hemorrhages, 7 cases of intracerebral bleeding, 3 SAHs plus intracerebral bleeding). Image quality of flat panel detector CT was considered sufficient in all cases supratentorially and in 92% in the posterior fossa. Regarding detection or exclusion of intracranial hemorrhage, flat panel detector CT reached a sensitivity, specificity, positive and negative predictive values, and accuracy of 58%, 85%, 44%, 91%, and 81%, respectively. Maximum attenuation measurements were not valuable for the differentiation of hemorrhage and BBB disruption.

CONCLUSIONS

Flat panel CT after endovascular stroke treatment was able to exclude the rare event of an intracranial hemorrhage with a high negative predictive value. Future studies should evaluate the predictive value of BBB disruptions in flat panel detector CT for the development of relevant hematomas.

Elevated cerebral blood volume contributes to increased FLAIR signal in the cerebral sulci of propofol-sedated children

BACKGROUND AND PURPOSE

Hyperintense FLAIR signal in the cerebral sulci of anesthetized children is attributed to supplemental oxygen (fraction of inspired oxygen) but resembles FLAIR hypersignal associated with perfusion abnormalities in Moyamoya disease and carotid stenosis. We investigated whether cerebral perfusion, known to be altered by anesthesia, contributes to diffuse signal intensity in sulci in children and explored the relative contributions of supplemental oxygen, cerebral perfusion, and anesthesia to signal intensity in sulci.

MATERIALS AND METHODS

Supraventricular signal intensity in sulci on pre- and postcontrast T2 FLAIR images of 24 propofol-sedated children (6.20 ± 3.28 years) breathing supplemental oxygen and 18 nonsedated children (14.28 ± 2.08 years) breathing room air was graded from 0 to 3. The Spearman correlation of signal intensity in sulci with the fraction of inspired oxygen and age in 42 subjects, and with dynamic susceptibility contrast measures of cortical CBF, CBV, and MTT available in 25 subjects, were evaluated overall and compared between subgroups. Factors most influential on signal intensity in sulci were identified by stepwise logistic regression.

RESULTS

CBV was more influential on noncontrast FLAIR signal intensity in sulci than the fraction of inspired oxygen or age in propofol-sedated children (CBV: r = 0.612, P = .026; fraction of inspired oxygen: r = -0.418, P = .042; age: r = 0.523, P = .009) and overall (CBV: r = 0.671, P = .0002; fraction of inspired oxygen: r = 0.442, P = .003; age: r = -0.374, P = .015). MTT (CBV/CBF) was influential in the overall cohort (r = 0.461, P = .020). Signal intensity in sulci increased with contrast in 45% of subjects, decreased in none, and was greater (P < .0001) in younger propofol-sedated subjects, in whom the signal intensity in sulci increased with age postcontrast (r = .600, P = .002).

CONCLUSIONS

Elevated cortical CBV appears to contribute to increased signal intensity in sulci on noncontrast FLAIR in propofol-sedated children. The effects of propofol on age-related cerebral perfusion and vascular permeability may play a role.

Subarachnoid hemorrhage: beyond aneurysms

OBJECTIVE

Spontaneous subarachnoid hemorrhage (SAH) typically prompts a search for an underlying ruptured saccular aneurysm, which is the most common nontraumatic cause. Depending on the clinical presentation and pattern of SAH, the differential diagnosis may include a diverse group of causes other than aneurysm rupture.

CONCLUSION

For the purposes of this review, we classify SAH into three main patterns, defined by the distribution of blood on unenhanced CT: diffuse, perimesencephalic, and convexal. The epicenter of the hemorrhage further refines the differential diagnosis and guides subsequent imaging. Additionally, we review multiple clinical conditions that can simulate the appearance of SAH on CT or MRI, an imaging artifact known as pseudo-SAH.

Colocalization of gadolinium-diethylene triamine pentaacetic acid with high-molecular-weight molecules after intracerebral convection-enhanced delivery in humans

BACKGROUND

Convection-enhanced delivery (CED) permits site-specific therapeutic drug delivery within interstitial spaces at increased dosages through circumvention of the blood-brain barrier. CED is currently limited by suboptimal methodologies for monitoring the delivery of therapeutic agents that would permit technical optimization and enhanced therapeutic efficacy.

OBJECTIVE

To determine whether a readily available small-molecule MRI contrast agent, gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA), could effectively track the distribution of larger therapeutic agents.

METHODS

Gd-DTPA was coinfused with the larger molecular tracer, I-labeled human serum albumin (I-HSA), during CED of an EGFRvIII-specific immunotoxin as part of treatment for a patient with glioblastoma.

RESULTS

Infusion of both tracers was safe in this patient. Analysis of both Gd-DTPA and I-HSA during and after infusion revealed a high degree of anatomical and volumetric overlap.

CONCLUSION

Gd-DTPA may be able to accurately demonstrate the anatomic and volumetric distribution of large molecules used for antitumor therapy with high resolution and in combination with fluid-attenuated inversion recovery (FLAIR) imaging, and provide additional information about leaks into cerebrospinal fluid spaces and resection cavities. Similar studies should be performed in additional patients to validate our findings and help refine the methodologies we used.

A High CSF Signal on FLAIR: It Is Not Always Blood

We describe a patient with progressive neurologic deficit due to middle cerebral branch occlusion. Temporary partial balloon occlusion of the abdominal aorta led to an increased signal in the subarachnoid space on fluid-attenuated inversion recovery images with no evidence of subarachnoid hemorrhage. After spontaneous recanalization, the increased signal of the subarachnoid space returned to normal. We assume that signal changes in the subarachnoid space were due to a temporary increase in blood volume in the superficial brain vessels.

Imaging of the meninges and the extra-axial spaces

The separate meningeal layers and extraaxial spaces are complex and can only be differentiated by pathologic processes on imaging. Differentiation of the location of such processes can be achieved using different imaging modalities. In this pictorial review we address the imaging techniques, enhancement and location patterns, and disease spread that will promote accurate localization of the pathology, thus improving accuracy of diagnosis. Typical and unusual magnetic resonance (MR), computed tomography (CT), and ultrasound imaging findings of many conditions affecting these layers and spaces are described.

Biodistribution of gadolinium-based contrast agents, including gadolinium deposition

The biodistribution of approved gadolinium (Gd)-based contrast agents (GBCAs) is reviewed. After intravenous injection GBCAs distribute in the blood and the extracellular space and transiently through the excretory organs. Preclinical animal studies and the available clinical literature indicate that all these compounds are excreted intact. Elimination tends to be rapid and, for the most part, complete. In renally insufficient patients the plasma elimination half-life increases substantially from hours to days depending on renal function. In patients with impaired renal function and nephrogenic systemic fibrosis (NSF), the agents gadodiamide, gadoversetamide, and gadopentetate dimeglumine have been shown to result in Gd deposition in the skin and internal organs. In these cases, it is likely that the Gd is no longer present as the GBCA, but this has still not been definitively shown. In preclinical models very small amounts of Gd are retained in the bone and liver, and the amount retained correlates with the kinetic and thermodynamic stability of the GBCA with respect to Gd release in vitro. The pattern of residual Gd deposition in NSF subjects may be different than that observed in preclinical rodent models. GBCAs are designed to be used via intravenous administration. Altering the route of administration and/or the formulation of the GBCA can dramatically alter the biodistribution of the GBCA and can increase the likelihood of Gd deposition. J. Magn. Reson. Imaging 2009;30:1259-1267. (c) 2009 Wiley-Liss, Inc.

Isolated acute nontraumatic cortical subarachnoid hemorrhage

Our aim was to review the etiologic background of isolated acute nontraumatic cSAH. While SAH located in the basal cisterns originates from a ruptured aneurysm in approximately 85% of cases, a broad spectrum of vascular and even nonvascular pathologies can cause acute nontraumatic SAH along the convexity. Arteriovenous malformations or fistulas, cortical venous and/or dural sinus thrombosis, and distal and proximal arteriopathies (RCVS, vasculitides, mycotic aneurysms, Moyamoya, or severe atherosclerotic carotid disease) should be sought by noninvasive imaging methods or/and conventional angiography. Additionally, PRES may also be a source of acute cSAH. In elderly patients, cSAH might be attributed to CAA if numerous hemorrhages are demonstrated by GRE T2 images. Finally, cSAH is rarely observed in nonvascular disorders, such as abscess and primitive or secondary brain tumors.