2017 Sec 1 Green Book

Fig 19. Axial (A, B) and coronal (C) contrast-enhanced CT images in soft tissue window of a child with cervical lymphadenitis as a consequence of a bacterial infection of the upper respiratory tract. Multiple enlarged reactive lymph nodes are demonstrated in the right upper cervical region (A). Some of the involved lymph nodes appear as confluent lesions (A). Liquefaction and suppuration causes the central part of the lymph node to become hypodens (B, C). Subsequent abscess formation is shown by extranodal extension (B, C). Note the unilateral lymph node involvement as frequently occurs in case of bacterial infection.

single from multiple lymph node group involvement and takes into account if the lymph node groups are located on the same side or on both sides of the diaphragm, bulk size, extranodal sites of disease, and presence of clinical symptoms (B-symptoms including night sweating, weight loss, and malaise). Non-Hodgkin lymphoma is more common than Hodgkin lymphoma in children younger than 10 years of age. Four subtypes are differentiated in the World Health Organiza- tion (WHO) classification: Burkitt lymphoma, diffuse large B-cell lymphoma, anaplastic large cell lymphoma, and lym- phoblastic lymphoma. Cervical non-Hodgkin lymphoma is of- ten accompanied by disseminated disease. Furthermore, non- Hodgkin lymphoma may involve extranodal lymphatic sites (eg, Waldeyer ring) or other extranodal sites (eg, jaw) in the cervical region. In the pediatric age group, cervical extranodal disease in non-Hodgkin lymphoma is less common than in other body parts. 5 In 2015, a new staging system for the pedi- atric age group has been introduced based on identification of new pathologic entities, improvements in cytogenetic, molec- ular, and immunophenotypic characterizations of disease and major advances in imaging applicable to childhood and ado- lescent non-Hodgkin lymphoma. The revised International Pe- diatric Non-Hodgkin Lymphoma Staging System (IPNHLSS) maintains the general structure of the St. Jude staging system and introduces some modifications and more explicit indica- tions on peculiar sites of disease. 65 The staging system basically assesses tumor load and differentiates limited disease form ex- tensive disease. Rhabdomyosarcoma Rhabdomyosarcoma is the most common soft tissue sarcoma in children younger than 5 years of age. Forty percent of the rhab- domyosarcomas are located in the head and neck region. 1,5,66 The lesion generally manifests in the first decade of life and demonstrates a slight male predominance. There are three prin- cipal histologic subtypes acknowledged, the embryonal, alveo- lar, and pleomorphic type. The embryonal subtype has in gen- eral a better prognosis, whereas alveolar rhabdomyosarcomas belong to the most aggressive types. Tumors of the embryonal subtype account for 60% of the rhabdomyosarcomas, and there- fore site of origin of the tumor in the head and neck region is associated with favorable outcome. Head and neck rhab- domyosarcomas are categorized into orbital, parameningeal

the abscess due to reduced water mobility within the pus. 2 Ad- ditional MRA and MRV imaging sequences may be of great value to exclude associated vascular complications, eg, venous thrombosis or development of Lemierre’s syndrome. Lymphoma Lymphoma is the most common malignancy arising from the head and neck region in the pediatric population (55% of head and neck tumors in children). In general, lymphomas account for 10–15% of all childhood malignancies. 1,5 The lesion typi- cally presents as a painless posterior neck mass or supraclavic- ular mass, often in association with lymph node enlargement in other cervical regions. The vast majority of cervical lymph node enlargement in children is the result of viral or bacterial upper respiratory tract infection. Persistent nodal enlargement (for more than 6 weeks) requires further evaluation. 5 On US (including color Doppler), features differentiating nodal malig- nancies from benign reactive lymph nodes include increased size ( > 3 cm in longest diameter), round shape, decrease in internal echogenicity, loss of normal echogenic hilum, detec- tion of peripheral subcapsular vessels, and focal areas of absent perfusion. 1,5 Currently, disease staging of lymphoma is prefer- ably performed with CT of the neck, chest, abdomen, and pelvis. Lymph nodes demonstrating a short axis > 2 cm are con- sidered to be involved in the disease process. For intermediate- sized lymph nodes (10-20 mm), radiotracer uptake on positron emission tomography (PET) indicates involvement. 5 MR imag- ing is typically used for evaluation of central nervous sys- tem involvement. However, diffusion-weighted MR imaging sequences may also play a role in differentiating involved from noninvolved lymph nodes by calculating the mean apparent diffusion coefficient (ADC) value. The ADC value of involved lymph nodes is significantly lower compared to noninvolved lymph nodes due to the high cellularity in lymphoma. 2 The future role for PET MR imaging in the staging of this disease is promising. Hodgkin lymphoma is more common in adolescents. The classical appearance of Hodgkin lymphoma is involvement of contiguous lymph node groups. Coexistent mediastinal lymph node involvement is common. The disease is often confined to the neck and chest region (Fig 20). Staging of disease is performed according to the Cotswold modification of the Ann Arbor staging system. 5,64 The staging system differentiates

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