2017 Sec 1 Green Book

aspect of the superior paralaryngeal space is identified. Lesions of the internal type are limited by the thyrohyoid membrane (Fig 8). External and combined types are located superficial to thyrohyoid membrane at the point of insertion of the neurovas- cular bundle (superior laryngeal nerve, vessels). Laryngoceles will typically demonstrate a connection to the laryngeal cavity. The echogenicity and MR signal intensity of the lesions depend on the amount of air or mucus secretions. 12 Congenital Inclusion Cysts Dermoid and epidermoid cysts are congenital inclusion cysts and originate from entrapped epithelial elements along embry- onic lines of fusion during development. These cysts are lined by squamous epithelium. Dermoid cysts are more commonly encountered than epidermoid cysts in this region. Seven per- cent of all dermoids and epidermoids occur in the head and neck region. 6 The clinical distinction between dermoid and epidermoid cysts is hard to make and in the majority of cases insignificant. Dermoid cysts are commonly located in the midline of the neck, the floor of the mouth, and the submandibular or the sublingual spaces (Fig 9). The lesion manifests as a slow- growing asymptomatic mass during childhood or young adult- hood. Rapid enlargement of the lesion may occur in associ- ation with a sinus tract and is possibly due to an increase in desquamation. 3,12 Dermoid cysts contain variable amounts of dermal derivatives such as fluid, lipid material, cholesterol, ker- atinaceous debris, calcification, and hair. Depending on the content of the cyst, the imaging features may vary. Typical imaging findings include a moderately thin-walled unilocular mass with fat and/or calcifications and no contrast enhance- ment on MR imaging. US typically demonstrates a pseudosolid mass due to mixed internal echoes of proteinaceous material, fat, and calcifications. The presence of posterior acoustic en- hancement on ultrasound reveals the cystic nature of the mass. On fat-saturated MR sequences, the fatty elements show sig- nal dropout. The “sack-of-marbles” appearance, due to coales- cence of fat into small nodules, is pathognomonic for a der- moid cyst. In some cases, fluid/fluid or fluid/debris levels are demonstrated. Local mass effect with displacement of the adja- cent structures may occur. Commonly, a sinus tract toward the skin surface is identified. The lesion typically shows no move- ment related to tongue protrusion or swallowing on US. In rare instances, dermoids may have fibrous attachments to the

hyoid and may consequently move with protrusion of the tongue (similar to thyroglossal duct cyst). The topographic re- lationship of the dermoid cyst inferior or superior to the mylo- hyoid muscle can be determined in the coronal plane and is an important preoperative information to help choose between an external or intraoral approach. 3,6 Lack of enhancement differ- entiates these lesions from teratomas with solid components. Epidermoid cysts are typically located off-midline or asym- metric to one side of the midline at the base of the tongue or in the anterior cervical triangle. They often become evident during infancy. The degree of proteinaceous fluid in the epidermoid cyst varies. On imaging, the cystic structure is relatively well circumscribed. A predominantly fluid filled structure is seen on US. MR imaging shows either subtle T1 hypointensity or T1 hyperintensity depending on the protein content. 18 Although presence of restricted diffusion has been initially associated with epidermoids, restricted diffusion is not pathognomonic of epi- dermoid cysts and can also be seen with dermoid cysts. 3,30 Both lesions may demonstrate significant overlap in imag- ing features and to a lesser degree in location. Identification of these cysts as inclusion cysts and confirming the presence or absence of a track is most useful for management of these cases. 31 Bronchogenic Cyst Cervical bronchogenic cysts are extremely rare congenital foregut anomalies. The etiology for the aberrant position of the lesion in the neck is unclear. The lesion manifests in infancy as an asymptomatic neck mass or as a draining sinus. There is a male predilection. Imaging features comprise a well-defined cystic structure in the sternal notch region anterior to the tra- chea (Fig 10). The cyst or sinus tract can become infected and evolve into a neck abscess. 3,12

Congenital Solid Masses Teratoma

Teratomas in the cervical region account for 2–5% of all germ cell tumors and 10% of all teratomas. The lesions are often identified on prenatal imaging (Fig 11). In the postnatal pe- riod, they generally present before the age of 3 years as a large firm mass in the neck region and depending on the location with complicating airway obstruction/compression. There is a slight female predominance. Teratomas are composed of all

Fig 9. Axial fat-suppressed T2-weighted (A) and contrast enhanced fat-suppressed T1-weighted (B, C) MR images of a child with a dermoid cyst. The images demonstrate a well-defined, thin-walled cystic structure in the left lateral neck. On the contrast-enhanced T1-weighted (B, C) images, the anterolateral location of the cyst in relation to the carotid space is well demonstrated. Note that this precise location differentiates this lesion from a second branchial cleft anomaly (typical lateral to carotid space).

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

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