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Background
Head and neck cancer comprises 12% of all childhood malignancies. The most common pediatric head and neck tumors include lymphoma, rhabdomyosarcoma, thyroid carcinoma, nasopharyngeal carcinoma, salivary gland malignancies and neuroblastoma; other malignancies like soft tissue sarcomas, cutaneous tumors, metastases, and Langerhans cell histiocytosis are rare. Imaging modality recommendation is based on the site of disease. Primary: MRI with and without contrast. Local and regional spread: MRI with and without contrast, CT neck with contrast, and PET/CT. Metastasis: PET/CT and CT chest with contrast.

Educational Goals / Teaching Points
Head and neck masses are a common presenting complaint in the pediatric population with a broad and varied differential. Imaging plays a vital role in differentiating these entities and guiding in management with CT being particularly useful for assessing the patient in more acute scenarios when there is concern for airway obstruction. Nuclear medicine scintigraphy has a role in specific circumstances and can aid in staging in the presence of malignancy.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
MRI is generally the preferred imaging method for assessing head and neck masses in children, while CT is useful for characterizing changes of the bone. MRI provides signal intensity and vascular flow characteristics, enhancement patterns, location, and extent of the masses. High-spatial-resolution, contrast-enhanced, and fat-saturated sequences are essential for evaluating the small anatomic spaces of the orbit. On MR images, rhabdomyosarcoma may appear isointense to hyperintense on T1-weighted images with respect to normal extraocular muscle and show variable signal intensity on T2-weighted images. RMS usually shows reduced diffusivity, variable enhancement, and hypermetabolism at PET. Neuroblastoma on MR images, the soft-tissue mass is typically hypointense on T1-weighted images and slightly hyperintense on T2-weighted images relative to muscle and shows avid enhancement. Differentials include leukemia/lymphoma and Langerhans cell histiocytosis. Langerhans cell histiocytosis on CT is seen as extensive destruction of the temporal bone involving the mastoid, with the squamous part and the middle ear being less affected. The lesions have indistinct margins, and the smaller structures of the bony labyrinth and auditory ossicle chain may show erosion.

Conclusion
The goal of imaging is to maximize spatial and contrast resolution and minimize noise; this is of utmost importance in the imaging of pediatric head and neck tumors. The spaces of the head and neck are complex, and a small volume of anatomy may contain several tissue types separated by thin anatomic boundaries. Violation of these boundaries by tumors is important in staging and surgical planning.