More than just Langerhans cell histiocytosis: a radiologic review of histiocytic disorders.

Although Langerhans cell histiocytosis (LCH) is a familiar entity to most radiologists and to pediatric radiologists in particular, it is but one of a group of disorders caused by the overproduction of histiocytes, a subtype of white blood cells. Other less familiar diseases in this category are Erdheim-Chester disease (ECD), juvenile xanthogranuloma (JXG), Rosai-Dorfman disease (RDD), and hemophagocytic lymphohistiocytosis (HLH). This review describes the classification system, clinical manifestations, and pathophysiology of each disease, with particular attention to differential radiographic findings, including typical locations of involvement and varying appearances at radiography, computed tomography, magnetic resonance imaging, ultrasonography, and nuclear medicine imaging. Although LCH has a wide variety of manifestations and appearances, classic imaging findings include vertebra plana, skull lesions with a beveled edge, the "floating tooth" sign, bizarre lung cysts, and an absent posterior pituitary bright spot with infundibular thickening. The classic imaging findings of ECD are a perirenal rind of soft tissue and patchy long bone osteosclerosis. RDD has more nonspecific imaging findings, including lymphadenopathy (most commonly cervical) and intracranial lesions. Imaging findings in HLH are broad, with the most common abnormalities being hepatosplenomegaly, cerebral volume loss, and periventricular white matter abnormalities. JXG can manifest at imaging, but radiology does not play a major role in diagnosis. Familiarity with these disorders and their associated imaging findings facilitates correct and timely diagnosis. Imaging also features prominently in the assessment of treatment response.

A test of the role of two prefrontal/ subcortical networks in the "sequencing" of non-motor, visuo-spatial information.

There are a number of prefrontal/sub-cortical networks in the brain (e.g., cerebellar-thalamic-prefrontal or basal ganglia/supplementary motor cortex circuits) that despite having a clear role in motor function have been shown to be involved in non-motor tasks. In this project we test for the involvement of these networks in a dimensional judgment task that utilizes visual perceptual, visual spatial processing and requires the ordering of dimensional (height) information. Unlike previous studies examining non-motor sequencing, we directly compare both non-motor and motor versions of our dimensional judgment task. In addition, we examine activation uniquely associated with correct task responses. The findings provide evidence for the role of cortical not subcortical structures in the sequencing of visuo-spatial material apart from any motor output requirements. Our results suggest that the inferior parietal cortex (BA 7, 40) and medial frontal regions (BA 6, 8, 9 including the SMA) are instrumental to the task. Based on these results, we propose a prefrontal/parietal network plays a role in the implementation of a comparator mechanism that makes accurate comparisons along the dimension of interest, holds the information in working memory, and then (regardless of whether the information is correct or incorrect) generates a tag or abstract code that assigns the information a place in an ordered sequence. Most important, the information involved can be visual/symbolic and non-motor (not just motor) in nature.