Persistent Pulmonary Arteriovenous Malformations: Percutaneous Embolotherapy.

Pulmonary arteriovenous malformations (PAVM) are an uncommon entity that interventional radiologists may face in their clinical practice. Many of these lesions are treated successfully using endovascular techniques with satisfactory long-term results. However, some PAVMs respond poorly to initial interventional techniques. This article reviews the signs and symptoms of persistent PAVMs, illustrates different imaging modalities used to diagnose these lesions, and outlines mechanisms by which these lesions may persist. The article highlights techniques and embolic agents used for percutaneous transcatheter embolotherapy of persistent PAVMs and discuss the outcomes of these interventions.

Central Venous Occlusion in the Hemodialysis Patient.

Central venous stenosis (CVS) is encountered frequently among hemodialysis patients. Prior ipsilateral central venous catheterization and cardiac rhythm device insertions are common risk factors, but CVS can also occur in the absence of this history. Chronic CVS can cause thrombosis with partial or complete occlusion of the central vein at the site of stenosis. CVS is frequently asymptomatic and identified as an incidental finding during imaging studies. Symptomatic CVS presents most commonly as an upper- or lower-extremity edema ipsilateral to the CVS. Previously unsuspected CVS may become symptomatic after placement of an ipsilateral vascular access. The likelihood of symptomatic CVS may be affected by the central venous catheter (CVC) location; CVC side; duration of CVC dependence; type, location, and blood flow of the ipsilateral access; and extent of collateral veins. Venous angiography is the gold standard for diagnosis. Percutaneous transluminal angioplasty and stent placement can improve the stenosis and alleviate symptoms, but CVS typically recurs frequently, requiring repeated interventions. Refractory symptomatic CVS may require ligation of the ipsilateral vascular access. Because no available treatment option is curative, the goal should be to prevent CVS by minimizing catheters and central vein instrumentation in patients with chronic kidney disease and dialysis patients.

A Model for Mountain Pine Beetle Outbreaks in an Age-Structured Forest: Predicting Severity and Outbreak-Recovery Cycle Period.

The mountain pine beetle (MPB, Dendroctonus ponderosae), a tree-killing bark beetle, has historically been part of the normal disturbance regime in lodgepole pine (Pinus contorta) forests. In recent years, warm winters and summers have allowed MPB populations to achieve synchronous emergence and successful attacks, resulting in widespread population outbreaks and resultant tree mortality across western North America. We develop an age-structured forest demographic model that incorporates temperature-dependent MPB infestations. Stability of fixed points is analyzed as a function of (thermally controlled) MPB population growth rates and indicates the existence of periodic outbreaks that intensify as growth rates increase. We devise analytical methods to predict outbreak severity and duration as well as outbreak return time. After incorporating a spatial aspect and controlling initial stand demographic variation, the model predicts cycle periods that fall within observed outbreak return time ranges. To assess future MPB impact on forests, we use climate model projected temperatures with our model-based approximation methods to predict potential severity of future outbreaks that reflect the effects of changing climate.

MRI in the workup of biliary tract filling defects.

Recent advances in magnetic resonance imaging (MRI) have made imaging the biliary tract faster while providing excellent anatomic reproduction of this duct system. MRI/MR-cholangiopancreatography (MRCP) has now become the first-line imaging procedure for many biliary tract problems. This work briefly discusses the MR techniques for biliary tree imaging and reviews MRI's role in the numerous diagnoses of filling defects in the biliary tract.