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Brain tumors are the second most common malignancy of childhood, accounting for approximately 20% of all childhood cancers. The estimated incidence ranges from 2.4 to 4.1 cases per 100,000 children per year. Although nearly 60% of patients are now cured, brain tumors are still the principal cause of pediatric cancer mortality. Pediatric brain tumors are classified by histology. Medulloblastoma is the most common malignant brain tumor, and low-grade astrocytoma is the most common benign tumor.

In patients with lymphoma, prognosis and treatment are related to the stage of disease at diagnosis, and accurate staging, therefore, is essential for proper management. The staging procedures currently used include history and physical examination; computed tomography (CT) of the chest, abdomen, and pelvis; bone marrow biopsy; and, occasionally, staging laparotomy. Radionuclide studies, including gallium scintigraphy, bone scintigraphy, and more recently, positron emission tomography (PET) with fluorine-18 fluorodeoxyglucose (18F-FDG) have been used as adjuncts for staging, follow-up, and prognosis in children with Hodgkin’s disease and non-Hodgkin’s lymphoma.

Neuroblastoma is the most common extracranial solid tumor of childhood. It comprises 8% to 10% of all childhood neoplasms. Neuroblastoma is derived from primordial neural crest cells that normally differentiate into the sympathetic nervous system. The prevalence is about 1 case per 7000 newborns. There are about 600 new cases in the United States per year, and over 90% occur in children less than 6 years old. The median age is 22 months. Most primary tumors occur within the abdomen, especially the adrenal gland, although they may arise from any site along the course of the sympathetic nervous system. Other common sites are paraspinal ganglia of the posterior mediastinum and abdomen. About 60% of patients have widely metastatic osseous disease at presentation.

The clinical applications of fluorine-18 fluorodeoxyglucose-positron emission tomography (18F-FDG-PET) imaging in adults have grown rapidly. However, only recently has this technology and the merged technology of PET and computed tomography (PET-CT) been extended to children and adolescents. Thus, information about the indications and utility of PET-CT in pediatric oncology is limited. This chapter discusses the initial experience with PET and PET-CT imaging of patients with Wilms’ tumor.

Musculoskeletal sarcomas represent a heterogeneous group of malignancies involving bone and soft tissue with a highly variable natural history and a correspondingly diverse range of potential therapeutic strategies. The choice of treatment is largely driven by prognostic factors but is also dependent on local expertise, resources, and philosophies and the particular clinical circumstances of individual patients. Important considerations include the type, grade, extent, and location of the tumor. Curative treatment approaches in osteogenic sarcoma combine surgery and chemotherapy. In Ewing sarcoma, chemotherapy is used, and local control is achieved by surgery, radiotherapy, or a combination of both (1-3).

Soft tissue sarcomas are a heterogeneous group of malignant neoplasms of mesenchymal origin. They account for approximately 1% of all cancer diagnoses and 7% of pediatric malignancies (1,2). Just over half of these patients eventually succumb as a result of the disease. Soft tissue sarcomas typically present as asymptomatic large masses within the retroperitoneum or the proximal lower limbs but can also affect other sites of the body. In adults, the most common histologic origins are liposarcomas (21%), malignant fibrous histiocytomas (MFHs) (20%), leiomyosarcomas (20%), fibrosarcomas (11%), and tendosynovial sarcomas (10%) (3). In children, rhabdomyosarcoma comprise approximately 70% of the soft tissue sarcomas (3). Despite this highly variable histopathologic origin, the three negative predictive factors at the time of initial diagnosis for disease-free survival are primary site in the superficial trunk or in the limbs, high tumor grade, and large tumor size, rather than the histologic origin (4).

Positron emission tomography (PET) is a new and powerful imaging tool that has been successfully employed to diagnose many adult tumors. Incidental tumor detection by PET has been reported (1-5), as well as detection of chronic cholecystitis, aspiration pneumonia, and other benign conditions (6-8). The implementation of this new technology has been slower in the pediatric population than in the adult population.

This chapter reviews the development of the normal brain primarily as studied with nuclear imaging methods, with an emphasis on radiopharmaceutical-based methods [positron emission tomography (PET), single photon emission computed tomography (SPECT), and PET-computed tomography (PET-CT)]. These methods retain unchallenged specificity and sensitivity for certain important neurochemical events. We will also cover advances in allied techniques, including magnetic resonance imaging (MRI)-based and electrophysiologic methods. The functional modalities of PET and SPECT are best studied concurrently with structural modalities, including MRI and CT. In selected cases, both functional MRI (fMRI) and nonimaging modalities such as magnetic resonance spectroscopy (MRS) allow for in vivo molecular speciation, and can be brought to bear as well as magnetoencephalography (MEG). The recent introduction of hybrid PET-CT methods introduces a further dimension by allowing direct comparison of functional and structural features in a fused data set. By including these intermodality comparisons we hope to provide a more integrated and mutually explanatory exposition of the imaging of normal brain development

Positron emission tomography (PET) and single photon emission computed tomography (SPECT) scans offer great promise in helping to unravel the scientific basis for neurodevelopmental and neuropsychiatric disorders. To date, results have been somewhat limited by the difficulty in obtaining adequate control groups, technical difficulties in studying children, small numbers of subjects, variable analytic methods, and the inability to repeat scans in order to understand the effects of development and intervention due to concerns about exposure to radiopharmaceuticals. Nonetheless, some consistent findings have emerged, and intriguing new results point toward future directions of study.

Positron emission tomography (PET) can be used to perform neurochemical and functional brain imaging studies. First, neurochemical imaging studies allow assessment of the regional distribution and quantitative measurement of neurotransmitters, enzymes, or receptors in the living brain. Benzodiazepine receptor binding scans are an example of neurochemical receptor studies that are used in the evaluation of children with epilepsy. Second, functional brain imaging studies can measure regional cerebral blood flow (rCBF) or glucose metabolism. These studies may be performed in the resting state when the child is not having seizures (interictal) or at the time of a seizure (ictal study). Seizure activation of the brain is accompanied by increases in rCBF and glucose consumption. Interictal fluorodeoxyglucose (FDG)-PET studies are most commonly performed in the clinical PET imaging evaluation of children with epilepsy at the present time. Although technically more challenging, ictal FDG- or rCBF-PET studies may be performed when children have frequent or predictable seizures.