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Bruce E. Pollock and John Huston III

Object. To determine the natural history of colloid cysts of the third ventricle in patients in whom the cysts were incidentally discovered, the authors retrospectively reviewed cases observed during the modern neuroimaging era (1974–1998).

Methods. During this 25-year interval, 162 patients with colloid cysts were examined and cared for at our center. Sixty-eight patients (42%) were thought to be asymptomatic with regard to their colloid cyst and observation with serial neuroimaging was recommended. The mean patient age was 57 years at the time of diagnosis (range 7–88 years) and the mean cyst size was 8 mm (range 4–18 mm). Computerized tomography scanning revealed a hyperdense cyst in 49 (84%) of 58 patients. Three patients were excluded from the study because they died of unrelated causes within 6 months of scanning and seven patients were lost to follow-up review. Clinical follow-up evaluation was available at a mean of 79 months (range 7–268 months) in the remaining 58 patients. The numbers of patients who participated in follow-up review at 2, 5, and 10 years after diagnosis were 40, 28, and 14, respectively. The incidences of symptomatic progression related to the cyst were 0%, 0%, and 8% at 2, 5, and 10 years, respectively. No patient died suddenly during the follow-up interval. Two (6%) of 34 patients in whom follow-up imaging was performed either exhibited cyst growth (one patient) or experienced hydrocephalus (one patient) at a mean of 41 months after diagnosis (range 4–160 months).

Conclusions. Patients in whom asymptomatic colloid cysts are diagnosed can be cared for safely with observation and serial neuroimaging. If a patient becomes symptomatic, the cyst enlarges, or hydrocephalus develops, prompt neurosurgical intervention is necessary to prevent the occurrence of neurological decline from these benign tumors.

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J. Kevin DeMarco and John Huston III

In this paper, the authors review the definition of high-risk plaque as developed by experienced researchers in atherosclerosis, including pathologists, clinicians, molecular biologists, and imaging scientists. Current concepts of vulnerable plaque are based on histological studies of coronary and carotid artery plaque as well as natural history studies and include the presence of a lipid-rich necrotic core with an overlying thin fibrous cap, plaque inflammation, fissured plaque, and intraplaque hemorrhage. The extension of these histologically identified high-risk carotid plaque features to human in vivo MRI is reviewed as well. The authors also assess the ability of in vivo MRI to depict these vulnerable carotid plaque features. Next, the ability of these MRI-demonstrated high-risk carotid plaque features to predict the risk of ipsilateral carotid thromboembolic events is reviewed and compared with the risk assessment provided by simple carotid artery stenosis measurements. Lastly, future directions of high-risk carotid plaque MRI are discussed, including the potential for increased clinical availability and more automated analysis of carotid plaque MRI. The ultimate goal of high-risk plaque imaging is to design and run future multicenter trials using carotid plaque MRI to guide individual patient selection and decisions about optimal atherosclerotic treatment strategies.

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Fredric B. Meyer, John Huston III, and Stephen S. Riederer

✓ The internal flow dynamics were assessed in 16 cerebral aneurysms by cine phase-contrast magnetic resonance (MR) angiography. Six of the aneurysms were associated with subarachnoid hemorrhage and 10 were unruptured. The ruptured aneurysms demonstrated a 51% ± 10% increase in volume between systole and diastole, while the increase in volume of the unruptured aneurysms was 17.6% ± 8.9% (p < 0.005). The ruptured aneurysms demonstrated an approximate 1.0- to 1.5-mm increase in diameter in at least one dimension during systole. There was no relationship between aneurysm size and volumetric increases. These findings suggest that cine phase-contrast MR angiography can detect structural weakness in the aneurysmal wall. Imaging techniques that can evaluate aneurysmal wall dynamics may be useful in therapeutic planning.

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Wouter I. Schievink, John Huston III, Vicente E. Torres, and W. Richard Marsh

✓ Autosomal dominant polycystic kidney disease (ADPKD) is a systemic disorder well known for its association with intracranial aneurysms. A series of patients with ADPKD who were screened for the presence of an intracranial aneurysm were reviewed and found to include an unexpectedly high number with intracranial arachnoid cysts.

Among 247 patients with ADPKD who underwent magnetic resonance imaging (180 cases) or high-resolution contrastenhanced computerized tomography (67 cases), there were 151 women and 96 men with a mean age of 44 years. Intracranial arachnoid cysts were found in 20 patients (8.1%) with ADPKD compared to two (0.8%) in a control group without ADPKD matched for age, sex, and method of imaging (p < 0.0001). Multiple intracranial arachnoid cysts were found in two patients. Polycystic liver disease was present in 17 (85.0%) of the 20 patients with intracranial arachnoid cysts compared to 119 (52.4%) of the 227 patients without (p < 0.004). Pineal cysts were found in two patients (0.8%) and choroid plexus cysts were found in three patients (1.2%) but this was not different from the control population. None of the intracranial cysts was symptomatic and none was treated surgically.

Intracranial arachnoid cysts are a relatively frequent incidental finding in patients with ADPKD, providing further support for the systemic nature of this disease. In the authors' experience with approximately 1500 patients with ADPKD, no complication has been encountered from an intracranial arachnoid cyst, suggesting that asymptomatic intracranial arachnoid cysts in patients with ADPKD require no treatment.

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Stephen P. Lownie and David M. Pelz

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Waleed Brinjikji, John Huston III, Alejandro A. Rabinstein, Gyeong-Moon Kim, Amir Lerman, and Giuseppe Lanzino

Carotid artery stenosis is a well-established risk factor of ischemic stroke, contributing to up to 10%-20% of strokes or transient ischemic attacks. Many clinical trials over the last 20 years have used measurements of carotid artery stenosis as a means to risk stratify patients. However, with improvements in vascular imaging techniques such as CT angiography and MR angiography, ultrasonography, and PET/CT, it is now possible to risk stratify patients, not just on the degree of carotid artery stenosis but also on how vulnerable the plaque is to rupture, resulting in ischemic stroke. These imaging techniques are ushering in an emerging paradigm shift that allows for risk stratifications based on the presence of imaging features such as intraplaque hemorrhage (IPH), plaque ulceration, plaque neovascularity, fibrous cap thickness, and presence of a lipid-rich necrotic core (LRNC). It is important for the neurosurgeon to be aware of these new imaging techniques that allow for improved patient risk stratification and outcomes. For example, a patient with a low-grade stenosis but an ulcerated plaque may benefit more from a revascularization procedure than a patient with a stable 70% asymptomatic stenosis with a thick fibrous cap.

This review summarizes the current state-of-the-art advances in carotid plaque imaging. Currently, MRI is the gold standard in carotid plaque imaging, with its high resolution and high sensitivity for identifying IPH, ulceration, LRNC, and inflammation. However, MRI is limited due to time constraints. CT also allows for high-resolution imaging and can accurately detect ulceration and calcification, but cannot reliably differentiate LRNC from IPH. PET/CT is an effective technique to identify active inflammation within the plaque, but it does not allow for assessment of anatomy, ulceration, IPH, or LRNC. Ultrasonography, with the aid of contrast enhancement, is a cost-effective technique to assess plaque morphology and characteristics, but it is limited in sensitivity and specificity for detecting LRNC, plaque hemorrhage, and ulceration compared with MRI.

Also summarized is how these advanced imaging techniques are being used in clinical practice to risk stratify patients with low- and high-grade carotid artery stenosis. For example, identification of IPH on MRI in patients with low-grade carotid artery stenosis is a risk factor for failure of medical therapy, and studies have shown that such patients may fair better with carotid endarterectomy (CEA). MR plaque imaging has also been found to be useful in identifying revascularization candidates who would be better candidates for CEA than carotid artery stenting (CAS), as high intraplaque signal on time of flight imaging is associated with vulnerable plaque and increased rates of adverse events in patients undergoing CAS but not CEA.

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Thanh G. Phan, John Huston III, Robert D. Brown Jr., David O. Wiebers, and David G. Piepgras

Object. The goal of this study was to determine the frequency of enlargement of unruptured intracranial aneurysms by using serial magnetic resonance (MR) angiography and to investigate whether aneurysm characteristics and demographic factors predict changes in aneurysm size.

Methods. A retrospective review of MR angiograms obtained in 57 patients with 62 unruptured, untreated saccular aneurysms was performed. Fifty-five of the 57 patients had no history of subarachnoid hemorrhage. The means of three measurements of the maximum diameters of these lesions on MR source images defined the aneurysm size. The median follow-up period was 47 months (mean 50 months, range 17–90 months).

No aneurysm ruptured during the follow-up period. Four patients (7%) harbored aneurysms that had increased in size. No aneurysms smaller than 9 mm in diameter grew larger, whereas four (44%) of the nine aneurysms with initial diameters of 9 mm or larger increased in size. Factors that predicted aneurysm growth included the size of the lesion (p < 0.001) and the presence of multiple lobes (p = 0.021). The location of the aneurysm did not predict an increased risk of enlargement.

Conclusions. Patients with medium-sized or large aneurysms and patients harboring aneurysms with multiple lobes may be at increased risk for aneurysm growth and should be followed up with MR imaging if the aneurysm is left untreated.

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Vance T. Lehman, Petrice M. Cogswell, Lorenzo Rinaldo, Waleed Brinjikji, John Huston III, James P. Klaas, and Giuseppe Lanzino

Numerous recent technological advances offer the potential to substantially enhance the MRI evaluation of moyamoya disease (MMD). These include high-resolution volumetric imaging, high-resolution vessel wall characterization, improved cerebral angiographic and perfusion techniques, high-field imaging, fast scanning methods, and artificial intelligence. This review discusses the current state-of-the-art MRI applications in these realms, emphasizing key imaging findings, clinical utility, and areas that will benefit from further investigation. Although these techniques may apply to imaging of a wide array of neurovascular or other neurological conditions, consideration of their application to MMD is useful given the comprehensive multidimensional MRI assessment used to evaluate MMD. These MRI techniques span from basic cross-sectional to advanced functional sequences, both qualitative and quantitative.

The aim of this review was to provide a comprehensive summary and analysis of current key relevant literature of advanced MRI techniques for the evaluation of MMD with image-rich case examples. These imaging methods can aid clinical characterization, help direct treatment, assist in the evaluation of treatment response, and potentially improve the understanding of the pathophysiology of MMD.

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Vance T. Lehman, Waleed Brinjikji, Mahmud Mossa-Basha, Giuseppe Lanzino, Alejandro A. Rabinstein, David F. Kallmes, and John Huston III

Intracranial aneurysms are heterogeneous in histopathology and imaging appearance. The biological behavior of different types of aneurysms is now known to depend on the structure and physiology of the aneurysm wall itself in addition to intraluminal flow and other luminal features. Aneurysm wall structure and imaging markers of physiology such as aneurysm wall enhancement have been assessed in many prior investigations using conventional-resolution MRI. Recently, high-resolution vessel wall imaging (HR-VWI) techniques with MRI have been introduced. Reports of findings on high-resolution imaging have already emerged for many types of aneurysms demonstrating detailed characterization of wall enhancement, thickness, and components, but many questions remain unexplored. This review discusses the key HR-VWI literature to date. Aneurysm wall findings on conventional-resolution MRI are also discussed as these may help one understand the potential utility and findings on HR-VWI for various aneurysm types. The authors have illustrated these points with several examples demonstrating both features already described in the literature and novel cases demonstrating the potential for future clinical and research applications.

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Kelly D. Flemming, David O. Wiebers, Robert D. Brown Jr., Michael J. Link, Hirofumi Nakatomi, John Huston III, Robyn McClelland, and Teresa J. H. Christianson

Object. Nonsaccular intracranial aneurysms (NIAs) are characterized by dilation, elongation, and tortuosity of intracranial arteries. Dilemmas in management exist due to the limited regarding the natural history of this disease entity. The objective of this study was to determine the prospective risk of subarachnoid hemorrhage (SAH) in patients with vertebrobasilar NIAs.

Methods. All patients with vertebrobasilar fusiform or dolichoectatic aneurysms that had been radiographically demonstrated between 1989 and 2001 were identified. These patients' medical records were retrospectively reviewed. A prospective follow-up survey was sent and death certificates were requested. Based on results of neuroimaging studies, the maximal diameter of the involved artery, presence of SAH, and measurements of arterial tortuosity were recorded. Nonsaccular intracranial aneurysms were classified according to their radiographic appearance: fusiform, dolichoectatic, and transitional. Dissecting aneurysms were excluded. The aneurysm rupture rate was calculated based on person-years of follow up. Predictive factors for rupture were evaluated using univariate analysis (p < 0.05). One hundred fifty-nine patients, 74% of whom were men, were identified. The mean age at diagnosis was 64 years (range 20–87 years). Five patients (3%) initially presented with hemorrhage; four of these patients died during follow up. The mean duration of follow up was 4.4 years (692 person-years). Nine patients (6%) experienced hemorrhage after presentation; six hemorrhages were definitely related to the NIA. The prospective annual rupture rate was 0.9% (six patients/692 person-years) overall and 2.3% in those with transitional or fusiform aneurysm subtypes. Evidence of aneurysm enlargement or transitional type of NIA was a significant predictor of lesion rupture. Six patients died within 1 week of experiencing lesion rupture.

Conclusions. Risk of hemorrhage in patients harboring vertebrobasilar NIAs is more common in those with evidence of aneurysm enlargement or a transitional type of aneurysm and carries a significant risk of death.