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INTRODUCTION

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Advances in technology have made possible the use of radiologic techniques to assist in diagnosis of a variety of disorders discussed throughout this text. Most significant in this regard have been the refinement of computer-assisted tomography (CT), the more widespread availability, power, and use of magnetic resonance imaging (MRI), and the introduction of tracer materials to further enhance their diagnostic utility. Additionally, ultrasonography (US) has been applied to the initial diagnostic approach in disorders such as gonadal tumors, where radiation exposure is distinctly undesirable. What follows in this chapter is an overview of the radiologic approach to diagnosis, with a summary of findings relevant to the disorders discussed.

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HYPOTHALAMIC-PITUITARY IMAGING

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The pituitary gland occupies the sella turcica, a cup-shaped depression of the sphenoid bone, and consists of the anterior (adenohypophysis), posterior pituitary lobe with embryologically distinct origins, and an intermediate lobe (pars intermedia) between the anterior and posterior lobe of the pituitary, a vestigial remnant usually not seen on imaging.

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Imaging Techniques
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MRI remains the mainstay for evaluation of the pituitary gland and hypothalamic region. The higher spatial and soft tissue resolution with lack of ionizing radiation are among the main advantages of MRI over CT. Current advances in MRI technology with higher magnetic field strength (3.0 Tesla), faster sequences, and improved multicoil (parallel imaging) acquisition have continued to improve MRI diagnosis with high-resolution anatomic detail. CT remains a viable tool for patients with contraindications for MR imaging, and can be performed coupled with navigator tools for surgical planning and superior depiction of bony anatomy. In addition, CT offers better visualization of calcification or bony erosion of the sellar floor, which can alter differential diagnosis in the evaluation of sellar and parasellar pathology.

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Pituitary Size and Signal Intensity on MRI
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There is considerable variability in the size, shape, and signal of normal pediatric pituitary glands.1 These factors should be considered within the context of the clinical scenario and glandular function. There is also pituitary gland size variability related to gender and age. Understanding of these changes is fundamental for adequate imaging evaluation. The normal pituitary gland in neonates is physiologically enlarged, with a concave superior margin. There is also increased hyperintensity on T1-weighted imaging of the gland at birth, and separating anterior from posterior lobe may be difficult. This is probably related to a combination of increased metabolic activity and influence of maternal hormones in the neonate. After 2 months of age the pituitary gland assumes the infant configuration with decreased size and progressive hypointensity on T1-weighted imaging of the anterior lobe, and after the first few months of life the gland has an adult appearance. There is stable hyperintensity on T1-weighted imaging of the posterior lobe through life in most patients, the so-called neurohypophyseal bright spot (Figure 52-1). The etiology of this high signal intensity on T1-weighted ...

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