2017 Sec 1 Green Book

extends into the anterior submandibular space through a defect

in the mylohyoid musculature.

On MR imaging, the maximal

volume of the cystic lesion is localized in the submandibular

space (Fig 16). A narrow T2 hyperintense tail originating from

the floor of the mouth can typically be identified, but is not

necessary to suggest the diagnosis. The cystic component of

a plunging ranula shows a more irregular shape than simple

ranulas. In incidental cases, a giant ranula may extend postero-

superiorly into the parapharyngeal space. Identification of the

narrow tail connecting to the sublingual space on MR imag-

ing may be an important diagnostic clue.

40,41

Plunging ranulas

have to potential to demonstrate trans-spatial extension, similar

to vascular malformations.

Laryngeal Anomalies

Laryngeal anomalies are uncommonly congenital, rarely

present during childhood, and are more commonly acquired

of the adult age. Laryngeal anomalies are described in detail in

the paragraph on congenital cystic lesions.

Acquired Solid Masses

Fibromatosis colli

, also called sternomastoid tumor of infancy

or congenital torticollis, has a reported prevalence of 0.4% of

live births.

In the majority of affected infants, there is a his-

tory of birth trauma, difficult delivery, or breech delivery. The

etiology is not clearly understood and in general terms, it is

caused by a reaction to trauma at or around birth. In addi-

tion, a genetic component is suspected due to positive family

history in affected infants.

1,43

Fibromatosis colli

is almost exclu-

sively encountered in the SCM muscle, although some cases

of involvement of the trapezius muscle have been reported. In

the 2002 WHO classification of soft-tissue tumors, the lesion

is categorized as a benign fibroblastic proliferation.

The le-

sion manifests as an enlarging unilateral neck mass or swelling

10–14 days after birth and may result in torticollis with ro-

tation of the head toward the side of the lesion. There is a

predilection for the right side. Because of the characteristic his-

tory and distinct features in physical exam of these lesions,

imaging is not always required. US may be useful to confirm

the diagnosis, demonstrating fusiform thickening in the caudal

two-third part of the SCMmuscle with homogeneous or hetero-

geneous echogenicity of the affected muscle. A rim of normal

peripheral muscle can be encountered. On US, synchronously

movement of the mass and the SCM muscle is a characteris-

tic imaging feature.

1,43,44

No further imaging is usually neces-

sary. If MR imaging is obtained, it may show mild increased

T2 signal and contrast enhancement as well as mass effect on

adjacent structures (Fig 17). Features suggestive of more aggres-

sive lesions (eg, soft-tissue sarcomas), for instance, involvement

of surrounding structures, vascular encasement, bone involve-

ment, or lymphadenopathy, can be excluded on MR imaging

studies.

Fibromatosis colli

typically regress spontaneously over a

period of 4–8 months.

4,43,44

Thyroid Mass

Thyroid masses are uncommon in the young age group, al-

though older teens and genetically predisposed children can

develop thyroid cancer. Diffuse enlargement is demonstrated

in association with thyrotoxicosis or Hashimoto thyroiditis. On

US, an abnormal echogenicity of the thyroid gland differen-

tiates Hashimoto thyroiditis from the preserved thyroid gland

echogenicity in thyrotoxicosis. In the pediatric population, focal

solid thyroid masses are rare and include adenomas, carcino-

mas, and lymphomas. Thyroid nodules in children are mainly

benign. There are no distinctive US, CT, or MR imaging fea-

tures to further characterize these solid lesion. On US, a well-

delineated diffuse anechoic or slight hypoechoic nodule with

or without a vascular rim favors a benign lesion.

An isotope

thyroid scan can identify “cold” nodules as an indication for

fine needle aspiration or biopsy.

Adenomas are the most common thyroid nodules in the pe-

diatric population. US demonstrates a hypoechoic mass relative

to the normal thyroid gland tissue, although cases of hypere-

choic and isoechoic adenomas are reported.

A hypoechoic

rim is hypothesized to represent pericapsular inflammatory in-

filtrate, compressed thyroid parenchyma or fibrous capsule.

Calcifications, cysts, and heterogeneous areas are due to hem-

orrhage or necrosis.

Multinodular goiter is rare in the pediatric age group. The

condition can result from congenital defects of thyroid hor-

mone synthesis, dietary iodine insufficiencies, or thyrotropic

medications. Imaging demonstrates an enlarged thyroid gland

with heterogeneous echogenicity and multiple scattered hyper-

echoic areas on US.

45,46

Thyroid carcinoma is very rare in children and comprises 1–

1.5% of all pediatric malignancies.

There is predilection for fe-

males in the age group from 7 to 12 years. Papillary thyroid car-

cinoma is the most common subtype in the pediatric age group

Fig 17.

Sagittal US image (A), axial fat-suppressed T2-weighted (B), and coronal contrast-enhanced fat-suppressed T1-weighted (C) MR

images of a child with

Fibromatosis colli

. The ultrasound image (A) demonstrates heterogeneous hyperechoic fusiform enlargement of the

caudal part of the sternocleidomastoid muscle. A rim of normal peripheral muscle is shown. The axial MR image (B) reveals mild increased

T2 signal intensity of the sternocleidomastoid muscle as well as mass effect on adjacent structures. The sagittal MR image (C) demonstrates

contrast enhancement of the sternocleidomastoid muscle.

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

183