Ritu Shah

Radiation Necrosis in the Brain: Imaging Features and Differentiation from Tumor Recurrence

Radiation necrosis in the brain commonly occurs in three distinct clinical scenarios, namely, radiation therapy for head and neck malignancy or intracranial extraaxial tumor, stereotactic radiation therapy (including radiosurgery) for brain metastasis, and radiation therapy for primary brain tumors. Knowledge of the radiation treatment plan, amount of brain tissue included in the radiation port, type of radiation, location of the primary malignancy, and amount of time elapsed since radiation therapy is extremely important in determining whether the imaging abnormality represents radiation necrosis or recurrent tumor. Conventional magnetic resonance (MR) imaging findings of these two entities overlap considerably, and even at histopathologic analysis, tumor mixed with radiation necrosis is a common finding. Advanced imaging modalities such as diffusion tensor imaging and perfusion MR imaging (with calculation of certain specific parameters such as apparent diffusion coefficient ratios, relative peak height, and percentage of signal recovery), MR spectroscopy, and positron emission tomography can be useful in differentiating between recurrent tumor and radiation necrosis. In everyday practice, the visual assessment of diffusion-weighted and perfusion images may also be helpful by favoring one diagnosis over the other, with restricted diffusion and an elevated relative cerebral blood volume being seen much more frequently in recurrent tumor than in radiation necrosis.

Imaging manifestations of progressive multifocal leukoencephalopathy.

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease caused by reactivation of JC virus in immunosuppressed patients. The diagnosis is usually suggested on imaging and confirmed by cerebrospinal fluid polymerase chain reaction (PCR) for JC virus DNA. In this article, we review the imaging manifestations of PML on computed tomography (CT), magnetic resonance imaging (MRI), diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), MR spectroscopy, single photon-emission computed tomography (SPECT) and positron-emission tomography (PET), and outline the role of imaging in follow-up and prognostication.

JC Virus Infection of the Brain

SUMMARY: Since its initial description, there have been significant changes in the epidemiology, pathogenesis, and clinical and imaging manifestations of JCV infection of brain. The most common clinical manifestation is PML. Other recently described CNS manifestations are JCE, JCVGCN, and JCM. Although AIDS is the most common predisposing factor for JCV reactivation, there is increasing incidence of brain manifestations of JCV reactivation in non-HIV settings, including different rheumatologic, hematologic, and oncologic conditions; monoclonal antibody therapy; transplant recipients; primary immunodeficiency syndromes; and even in patients without any recognizable immune deficiency. IRIS may develop secondary to restoration of immunity in HIV-positive patients with PML receiving antiretroviral therapy. This is of profound clinical significance and needs to be diagnosed promptly. Imaging plays a crucial role in the diagnosis of the disease, monitoring of treatment response, identifying disease progression, and predicting prognosis. In this article, current understanding of the epidemiology, pathogenesis, clinical presentations, and all aspects of imaging of JCV infection of the brain have been comprehensively reviewed.

Petrous Apex Lesions: Pictorial Review

Received January 19, 2010; accepted after revision August 4, 2010. 1Department of Radiology, Division of Neuroradiology, University of Alabama at Birmingham Medical Center, 619 19th St S, WP-150, Birmingham, AL 35249-6830. Address correspondence to A. K. Bag (abag@uabmc.edu). 2Present address: Department of Radiology, Edward Hines Jr VA Hospital, Hines, IL. AJR 2011; 196:WS26–WS37 0361–803X/11/1963–WS1

A Compartment-Based Approach for the Imaging Evaluation of Tinnitus

SUMMARY: Tinnitus affects 10% of the US general population and is a common indication for imaging studies. We describe a sequential compartment-based diagnostic approach, which simplifies the interpretation of imaging studies in patients with tinnitus. The choice of the initial imaging technique depends on the type of tinnitus, associated symptoms, and examination findings. Familiarity with the pathophysiologic mechanisms of tinnitus and the imaging findings is a prerequisite for a tailored diagnostic approach by the radiologist.

Diffusion Tensor Imaging in Hypertrophic Olivary Degeneration

SUMMARY: We report DTI and fiber tractography findings in a case of hypertrophic olivary degeneration. A 51-year-old man presented with an abnormal gait and visual difficulties. MR imaging showed enlargement of the right medullary olive and a vascular lesion in the right pontine tegmentum. Fiber tractography showed decreased volume of the right central tegmental tract, supporting a diagnosis of HOD.

Radiopaque Jaw Lesions: An Approach to the Differential Diagnosis

Radiopaque jaw lesions are frequently encountered at radiography and computed tomography, but they are usually underevaluated or underdescribed in radiology reports. A systematic approach to the evaluation of radiopaque jaw lesions is necessary to diagnose the lesion or at least provide a meaningful differential diagnosis. To evaluate a radiopaque jaw lesion, the first, most important step is to categorize the lesion according to its attenuation, its relationship to the teeth, and its location with respect to the tooth. These basic observations are essential to the evaluation of any type of jaw lesion. Once these observations have been made, it is easy to create a proper differential diagnosis. The presence of important characteristics, such as margination, a perilesional halo, bone expansion, and growth pattern, as well as whether the lesion is sclerotic, has ground-glass attenuation, or is mixed lytic and sclerotic, further narrows the differential diagnosis. It is important to note that some radiopaque jaw lesions may be entirely lucent early in their evolution. Awareness of the demographic distribution of these lesions and their associated clinical features, as well as the radiologic approach, is important to explore the terra incognita of radiopaque jaw lesions.

AJR Teaching File: Cavernous Sinus Mass in a Woman Presenting With Painful Ophthalmoplegia

Contrast-enhanced MRI of the brain revealed a homogeneously enhancing mass in the left cavernous sinus. The mass was isointense to gray matter on T2-weighted images. Enhancement extended into the left orbital apex through the superior orbital fissure, and there was enlargement and enhancement of several extraocular muscles. Enhancement also extended into the left pterygopalatine fossa through the foramen rotundum along the V2 division of the trigeminal nerve and into the infratemporal fossa through the foramen ovale along the V3 division of the trigeminal nerve (Fig. 1). Differential Diagnosis The differential diagnosis of an enhancing cavernous sinus mass includes idiopathic orbital apical inflammation with cavernous sinus involvement (Tolosa-Hunt syndrome), perineural tumor spread, meningioma, lymphoma, schwannoma, fungal infection, and sarcoidosis.

Imaging of Cavernous Sinus: Self-Assessment Module

The educational objectives for this self-assessment module are for the participant to exercise, self-assess, and improve his or her understanding of the anatomy of the cavernous sinus and clinicoradiologic features of common cavernous sinus diseases.

Strahlennekrose im Gehirn: Bildgebungsmerkmale und Abgrenzung zum Tumorrezidiv

Die Strahlennekrose im Gehirn tritt ublicherweise in 3 verschiedenen klinischen Szenarien auf: bei der Strahlentherapie von Kopf-Hals-Malignomen oder intrakraniellen extraaxialen Tumoren, bei stereotaktischer Strahlentherapie (einschlieslich der Radiochirurgie) zur Behandlung von Hirnmetastasen sowie bei der Strahlentherapie primarer Hirntumoren. Bei der Beurteilung, ob es sich bei der pathologischen Veranderung im Bildbefund um eine Strahlennekrose oder ein Tumorrezidiv handelt, ist die Kenntnis folgender Faktoren extrem wichtig: Bestrahlungsplan, Menge des im Bestrahlungsfeld liegenden Hirngewebes, Art der Strahlung, Lokalisation des Primarmalignoms und seit der letzten Bestrahlung verstrichene Zeit. Herkommliche Magnetresonanz-Bildgebungsbefunde dieser 2 Entitaten weisen eine betrachtliche Uberlappung auf, und sogar bei der histopathologischen Untersuchung ist eine Mischung aus Tumor und Strahlennekrose kein ungewohnlicher Befund. Bei der Differenzierung zwischen Tumorrezidiv und Strahlennekrose konnen moderne Bildgebungsmodalitaten, wie die Diffusionstensorbildgebung und die Perfusions-MR-Bildgebung (unter Berechnung bestimmter spezifischer Parameter, wie z.u200aB. des Quotienten der Werte des Apparent Diffusion Coefficient, der relativen Peak-Hohe und des Prozentsatzes der Signalerholung), die Magnetresonanzspektroskopie und die Positronenemissionstomografie als Hilfsmittel eingesetzt werden. In der taglichen Praxis ist fur die Abgrenzung der Diagnose ggf. auch die visuelle Beurteilung von diffusionsgewichteten und Perfusionsbildern hilfreich, wobei bei Tumorrezidiven Diffusionseinschrankungen und ein erhohtes relatives zerebrales Blutvolumen wesentlich haufiger beobachtet werden als bei der Strahlennekrose.