2017 Sec 1 Green Book

Fig 14. Axial T1-weighted (A), fat-suppressed T2-weighted (B), and contrast enhanced fat-suppressed T1-weighted (C) MR images of a child with an arteriovenous malformation. The T2-weighted images (B) show dark, serpiginous flow voids infiltrating the subcutaneous fat of the right cheek. The contrast-enhanced image (C) reveals an additional soft tissue infiltrating component of the lesion. Multiphasic dynamic contrast–enhanced MRA images (D-F) reveal early arterial enhancement of the lesion with feeders identified from the external carotid artery. Note the intralesional nidus formed by the tangle of vessels (E, F).

infantile hemangioma, carotid body tumors, glomus jugulare tu- mors, and juvenile nasopharyngeal angiofibromas (Table 2). 35 As only hemangiomas potentially present as a neck mass in the pediatric age group, this entity is discussed in greater detail in this review. Infantile hemangiomas represent one of the most common tumors of infancy with most lesions occurring in the head and neck (60%). The lesion initially presents as a red superficial skin lesion in the first couple weeks of life that was not visible at the time of birth. There is a female predilection with a female to male ratio of 3:1. 35 Infantile hemangiomas are benign vascular neoplasms. Several specific stages have been identified in the natural course of this entity. In the postnatal time period, the lesion starts to proliferate and enlarge rapidly and consists of hyperplastic proliferating endothelial cells (proliferative phase). At approximately 10 months of age, the hemangioma typically will gradually start to involute and shows progressive perivas- cular deposition of fibrofatty tissue (involution phase). About 50% of the lesions are completely resolved by the age of 5 years (involuted phase). 36,37 Favorable locations in the cervical region include subcutaneous lesions, subglottic lesions, and less common deep-seated lesions and lesions extending over mul- tiple tissue planes. Additional infantile hemangiomas may be identified in approximately 20% of the affected children. 35,36 Imaging reveals the exact anatomic location of the lesion, the extent of the lesion, and the relation to adjacent structures (Fig 15). On US, the hemangioma manifests as a well-defined lobulated heterogeneous lesion with high vascular flow on Doppler interrogation in the proliferative phase and fibrofatty features in the involuting phase. The most characteristic MR imaging feature of a proliferating infantile hemangioma is a well-defined solid mass that shows avid enhancement in the arterial phase. Additional multiphasic dynamic time-resolved

Arteriovenous Malformation AVM of the neck presents later in childhood or in the adoles- cent age group as skin discoloration with or without underlying compressible (pulsatile) mass. The lesion consists of enlarged feeding arteries draining into veins without an intervening capil- lary network. On Doppler US and multiphasic dynamic cMRA imaging studies, the lesions show a high-flow pattern as impor- tant differentiating feature from other vascular malformations. Furthermore, multiphasic time-resolved dynamic cMRA imag- ing studies may identify dilated feeding arteries and draining veins, early enhancement of the feeding arteries, and an in- tralesional nidus with shunting to draining veins and therefore early venous drainage. 7,8,37 Anatomic MR imaging sequences demonstrate no well-defined mass, but rather enlarged serpigi- nous flow voids with an additional soft tissue infiltrating compo- nent (Fig 14). Evaluation of extension of the lesion and poten- tial adjacent soft tissue and osseous involvement is important to determine. 35,36 Mixed-type Vascular Malformation Mixed-type vascular malformations are less common than solid-type lesion and mainly comprise mixed veno-lymphatic malformations; however, other mixed-type lesions may be iden- tified. These lesions demonstrate clinical features and imaging characteristics of the involved vascular malformations. Vascular Tumors Vascular tumors, particularly infantile hemangiomas, are com- mon in the pediatric population. These are neoplastic lesions manifesting with a high endothelial cell turnover. The growth of these lesions is independent of body size. Various vascular tumors are encountered in the head and neck region, including

Dremmen et al: Imaging Lumps and Bumps of the Neck in Children

181