Prashant Raghavan

Composition of the Stable Carotid Plaque Insights From a Multidetector Computed Tomography Study of Plaque Volume

Background and Purpose— Calcification has been associated with carotid plaque stability; however, an acceptable in vivo method to define plaques based on this component remains to be developed. The purpose of our study was to compare calcified and noncalcified volumes of carotid artery culprit symptomatic plaques with asymptomatic plaques using multidetector computed tomography. Methods— We identified 102 patients with ≥50% stenosis using NASCET criteria by multidetector computed tomography angiography between January 2004 and May 2006, which included 35 symptomatic (stenosis: 82.0±11.9%) and 67 asymptomatic patients (stenosis: 79.4±10.8%). Total plaque volume, noncalcified plaque volume, calcified plaque volume, and calcified/total ratio were measured for the 102 index plaques causing stenosis. Results— In a model including age, stenosis, and cardiovascular risk factors, calcified plaque volume/total plaque volume was significantly inversely associated with the occurrence of symptoms (P=0.012; odds ratio, 0.047; 95% CI, 0.004 to 0.511). There was a notable overlap in the calcified plaque volume/total plaque volume ratio between 0% and 45% for symptomatic and asymptomatic plaques. However, calcification >45% of the total plaque was very specific: 97.1% (34/35) for absence of symptoms (sensitivity: 28.4% 19/67). No significant association between total plaque volume, noncalcified plaque volume, or calcified plaque volume and symptomatology was found. Conclusion— The proportion of carotid plaque calcification, rather than absolute volume, is associated with stability in patients with stenosis. Specifically, for a subset of patients, plaque calcification >45% of the total volume may represent a clinically useful cutoff. The carotid plaque calcium ratio, determined by multidetector computed tomography volume measurements, may help noninvasively risk stratify patients with asymptomatic stenosis.

The Impact of Expansive Arterial Remodeling on Clinical Presentation in Carotid Artery Disease: A Multidetector CT Angiography Study

BACKGROUND AND PURPOSE: Atherosclerotic arterial remodeling has been described in the coronary circulation but has not been studied extensively for carotid atherosclerosis. The purpose of our study was to examine the association between carotid artery remodeling and clinical presentation in patients with significant stenosis by using multidetector row CT (MDCT). MATERIALS AND METHODS: One hundred eight patients with ≥50% stenosis (North American Symptomatic Carotid Endarterectomy Trial criteria) by MDCT angiography between January 2004 and June 2006 were identified. The study group included 37 symptomatic (65.9 ± 13.0 years; 12 women; stenosis, 81.5 ± 12.2%; 17 with stroke; 15 with transient ischemic attack; 5 with amaurosis fugax) and 71 asymptomatic patients (70.5 ± 10.5 years; 28 women; stenosis, 78.8 ± 11.1%). Remodeling ratio (RR) was calculated by dividing the outer vessel circumference at the site of greatest stenosis by a normal reference-segment vessel circumference. Maximum vessel thickness (MxVT) and eccentricity index (EI) of the plaque, defined as maximal thickness/minimal thickness at the site of greatest luminal narrowing, were also determined. Data were analyzed by using an independent t test. RESULTS: The RR was significantly higher in symptomatic patients (1.64 ± 0.44) than in asymptomatic patients (1.41 ± 0.5) (P=.02). There was no significant difference in MxVT in symptomatic (5.9 ± 2.1 mm) and asymptomatic patients (5.6 ± 2.4 mm) (P=.45) and no significant difference in EI (symptomatic, 4.7 ± 2.7; asymptomatic, 4.3 ± 2.2; P=.38). CONCLUSION: In this series of subjects with significant internal carotid artery stenosis, expansive carotid remodeling was significantly greater in patients with cerebral ischemic symptoms than in asymptomatic patients. The extent of expansive remodeling may indicate underlying atherosclerotic plaque vulnerability. MDCT has a role in the evaluation of carotid artery disease beyond examining luminal stenosis.

Imaging of the Facial Nerve

A variety of congenital, traumatic, vascular, inflammatory, and neoplastic processes may affect the facial nerve. Prudent use of CT and MR imaging combined with a complete understanding of facial nerve anatomy helps in narrowing the differential diagnosis. The precise anatomic course of the facial nerve must be charted in patients who undergo middle ear surgery. Also of great importance is recognition of the fact that the facial nerve may be affected in cancers of the head and neck by perineural spread. This article reviews the anatomy of the facial nerve and relevant, current clinical evaluation and imaging strategies.

Magnetic resonance imaging of sinonasal malignancies.

Objectives: To discuss common sinonasal malignancies with emphasis on squamous cell carcinoma and describe preoperative and postoperative magnetic resonance imaging evaluation for these lesions. Methods: Literature and institutional review. Results: Because of the large variety of the normal cell population, a variety of malignant neoplasms may occur in the sinonasal tract. For a large number of reasons, they are often advanced at the time of diagnosis and are difficult to treat given the complex anatomy of the sinonasal region and its proximity to critical structures. Magnetic resonance imaging is a vital tool in the diagnosis of these lesions and is used in conjunction with computed tomography to precisely delineate the extent of these neoplasms. Involvement of the skull base, the orbits, the intracranial compartment, and potential perineural spread of tumor can influence treatment options. Magnetic resonance is essential to evaluate these tumors. Conclusions: Magnetic resonance plays a vital role in the diagnosis of sinonasal neoplasms and is essential to accurately determine the precise extent of these tumors for treatment planning. It is also a useful tool in tumor surveillance.

Multimodal MR imaging model to predict tumor infiltration in patients with gliomas

IntroductionGliomas remain difficult to treat, in part, due to our inability to accurately delineate the margins of the tumor. The goal of our study was to evaluate if a combination of advanced MR imaging techniques and a multimodal imaging model could be used to predict tumor infiltration in patients with diffuse gliomas.MethodsInstitutional review board approval and written consent were obtained. This prospective pilot study enrolled patients undergoing stereotactic biopsy for a suspected de novo glioma. Stereotactic biopsy coordinates were coregistered with multiple standard and advanced neuroimaging sequences in 10 patients. Objective imaging values were assigned to the biopsy sites for each of the imaging sequences. A principal component analysis was performed to reduce the dimensionality of the imaging dataset without losing important information. A univariate analysis was performed to identify the statistically relevant principal components. Finally, a multivariate analysis was used to build the final model describing nuclear density.ResultsA univariate analysis identified three principal components as being linearly associated with the observed nuclear density (p values 0.021, 0.016, and 0.046, respectively). These three principal component composite scores are predominantly comprised of DTI (mean diffusivity or average diffusion coefficient and fractional anisotropy) and PWI data (rMTT, Ktrans). The p value of the model was <0.001. The correlation between the predicted and observed nuclear density was 0.75.ConclusionA multi-input, single output imaging model may predict the extent of glioma invasion with significant correlation with histopathology.

Extrapontine Myelinolysis Resulting in Transient Cortical Blindness

Central pontine myelinolysis and extrapontine myelinolysis are characterized by symmetric demyelination subsequent to rapid shifts in serum osmolality. Described here is a novel case of transient cortical blindness in association with imaging features of extrapontine myelinolysis, which occurred in a child with carbamoyl phosphate synthetase deficiency after rapid correction of hyperammonemia. Serum sodium levels were within normal limits at presentation and throughout the period of ammonia correction. A potential pathogenic mechanism of osmotic demyelination in the setting of acute treatment for hyperammonemia in a patient with a urea cycle abnormality includes disruption of the blood-brain barrier and re-equilibration of organic osmolytes, particularly glutamine.

Accuracy of MRI for the diagnosis of metastatic cervical lymphadenopathy in patients with thyroid cancer

PurposeThe aim of this study was to systematically compare a comprehensive array of magnetic resonance (MR) imaging features in terms of their sensitivity and specificity to diagnose cervical lymph node metastases in patients with thyroid cancer.Materials and methodsThe study included 41 patients with thyroid malignancy who underwent surgical excision of cervical lymph nodes and had preoperative MR imaging ≤4weeks prior to surgery. Three head and neck neuroradiologists independently evaluated all the MR images. Using the pathology results as reference, the sensitivity, specificity and interobserver agreement of each MR imaging characteristic were calculated.ResultsOn multivariate analysis, no single imaging feature was significantly correlated with metastasis. In general, imaging features demonstrated high specificity, but poor sensitivity and moderate interobserver agreement at best.ConclusionsCommonly used MR imaging features have limited sensitivity at correctly identifying cervical lymph node metastases in patients with thyroid cancer. A negative neck MR scan should not dissuade a surgeon from performing a neck dissection in patients with thyroid carcinomas.

Extramedullary hematopoiesis within the clivus: an unusual cause of lower cranial nerve palsy

AbstractWe report one year follow up of a case of extramedullary hematopoiesis within the clivus. The imaging findings, brief clinical course, and endoscopic transphenoidal approach are described. A 29-year-old female with thalassemia developed worsening cranial nerve signs. After imaging studies discovered a large clival mass, she underwent endoscopic transphenoidal biopsy of the lesion. Neural compression from exuberant erythrogenesis within tissue normally quiescent of red blood cell production was found to be the etiology of her neural deficit. Treatment for this condition is generally non-operative unless significant neural compression is present. Radiotherapy and anti-neoplastic agents have been used with success.

In vivo low frequency MR-guided thalamotomy with focused ultrasound: thermal vs mechanical lesioning in pig brain

The purpose of this study was to investigate the thresholds for inducing two possible means of tissue destruction with low frequency Magnetic Resonance guided Focused Ultrasound (MRgFUS): either mechanical lesioning in presence of ultrasonic cavitation or pure thermal lesioning (without cavitation).

AIDS Presenting as Granulomatous Amebic Encephalitis: PET and MR Imaging correlation

Granulomatous amebic encephalitis (GAE) is a rare and oftentimes fatal disease in immune compromised patients caused by free living amebae Acanthamoeba and Balamuthia. We report a patient in whom GAE secondary to Acanthamoeba was the initial presentation of acquired immunodeficiency syndrome in a 41‐year‐old male, and discuss the FDG positron emission tomography (PET) and magnetic resonance imaging findings that preceded the pathological diagnosis. The PET results provided complementary information when coupled with the MR brain findings. Improved understanding of the clinical and imaging findings of this deadly disease is the best hope for early diagnosis and treatment of this uncommon but deadly disease.