Case Report

Submitted by: Alaina Moore, MSIV

Faculty reviewer: Sandra Oldham, M.D

Date accepted: 24 August 2010

Radiological Category: Principal Modality (1):

Principal Modality (2):

Pediatrics

none

CT

Case History

11 year old female is referred from ENT for outpatient CT to evaluate soft tissue nodule of neck.

About 9 months prior, she presented to the ER with a painful nodule in the neck and was sent home with antibiotics.

No other medical history is available.

Radiological Presentations

Radiological Presentations

Radiological Presentations

Radiological Presentations

Radiological Presentations

Radiological Presentations

• Ectopic thyroid

• Thyroglossal duct cyst

• Dermoid cyst

• Lymphadenopathy

• Cystic hygroma

• Abscess

• Branchial cleft cyst

• Thymic cyst

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Test Your Diagnosis

There is a well-circumscribed, anterior, midline cyst that lies inferior to the hyoid bone and anterosuperior to the isthmus of the thyroid gland. It is of low density at approximately 25 HU and measures 20 mm x 7 mm x 15 mm. It appears to be separate from the thyroid gland. There are no calcifications, other masses, or inflammatory changes.

There is tonsillar hypertrophy. The airway is patent, the vascular structures are normal, and there are no bony abnormalities.

• Thyroglossal duct cyst

• Ectopic thyroid

• Dermoid cyst

• Branchial cleft cyst

• Cystic hygroma

• Thymic cyst

Findings:

Differentials:

Findings and Differentials

Thyroglossal Duct Cyst

The thyroid gland begins development in third week of gestation as an outgrowth from floor of pharynx at the foramen cecum. It descends through the neck, passing anterior to the developing hyoid bone. It should reach the inferior neck by the seventh week gestation. This primordial thyroid remains connected to the tongue by the thyroglossal duct. Involution usually occurs by the tenth week gestation. The distal end of the duct can become the pyramidal lobe of the thyroid. If a portion of the duct persists, secretion from the epithelial lining can form a cyst.

Thyroglossal duct cyst accounts for 70% of congenital neck anomalies.

75% are midline in location

80% are at the level of or inferior to the hyoid bone

The clinical presentation is usually of a gradually enlarging, painless, midline

neck mass in children and young adults which moves upward with tongue

protrusion. Cyst is often discovered when it becomes infected.

Discussion

Imaging• Ultrasound: Initial imaging modality of choice. Cyst appears anechoic and

well-circumscribed. Most are unilocular with thin walls. In the case of prior infection or hemorrhage, may appear heterogenous with internal echoes.

• CT: Appear as smooth, well-circumscribed cysts at midline near the hyoid bone. They have thin walls and are usually unilocular, although occasionally have septations. They have homogenous fluid or mucoid attenuation of 10-25 HU.

• MRI: Homogenous low signal on T1. Homogenous high signal on T2 because of fluid content of cyst.

Treatment• Preoperative ultrasound is perfomed to demonstrate normal thyroid tissue. The

thyroglossal duct remnant as well as the central portion of the hyoid bone and cuff of tissue around the tract from the hyoid to the foramen cecum are removed with the Sistrunk procedure to reduce likelihood of recurrence.

Discussion

Radiological Presentations

Thyroglossal duct cyst on ultrasound. Ahuja et al. Clinical Radiology 2005; 60:141-148.

Ectopic Thyroid

Ectopic thyroid results from failure of thyroid tissue to completely descend into the inferior neck. 90% are found at the base of the tongue, but can also occur anywhere along the thyroglossal duct.

Ectopic thyroid in the presence of suspected thyroglossal duct cyst is about 1-2%.

Before surgery to remove the mass, preoperative ultrasonography should be performed to show normal thyroid with homogenous echogenicity to rule out ectopic thyroid. Patients at high risk (hypothyroid, abnormal TFTs) can have thyroid scintigraphy to confirm thyroid location before surgery.

Discussion

Dermoid Cyst

Manifest in the 2nd to 3rd decade of life

7% occur in the head and neck with the most common location in the neck being at the base of the tongue.

Appear as mobile, midline, slow growing mass

In contrast to thyroglossal duct cysts, they are not in close association with the hyoid bone.

Can range in size from a few mm to 12 cm

Lined with squamous epithelium and can contain sebaceous glands, hair follicles, and sweat glands

Discussion

Imaging• US: well-circumscribed mass with multiple echogenic foci

• CT: Appears as thin walled, unilocular mass which is filled with a homogenous, hypoattenuating fluid. Can have characteristic “sack of marbles” appearance due to fat within the fluid. Can also see fluid-fluid levels. May also appear heterogenous due to epithelial secretions.

• MRI: Variable signal intensity on T1. Usually hyperintense on T2 with clearly demarcated rim and heterogenous internal appearance

Discussion

Dermoid cyst. Koeller K K et al. Radiographics 1999;19:121-146.

Branchial Cleft Cyst

95% of branchial cleft anomalies come from the 2nd branchial cleft, 75% of which are cysts. The most common location is anterior to the SCM and lateral to the carotids. They clinically present as painless masses on the lateral neck that enlarge slowly over time.

Imaging• US: appears as sharply marginated, round to ovoid, centrally anechoic mass

with thin wall

• CT: well-circumscribed, homogenous, hypoattenuated with thin wall

• MRI: fluid varies from hypointense to slightly hyperintense compared to muscle on T1, hyperintense on T2

Discussion

Cystic Hygroma

Most common form of lymphangioma

Arises from embryonic lymphatic channels

80% involve the head and neck. In children, most common location is posterior cervical space. In adults, it is seen in sublingual, submandibular, and parotid spaces.

They can cross fascial planes because they are very infiltrative.

Clinically, often present asymptomatically with painless mass in neck. They are variable in size and can become greater than 10 cm, compressing the airway.

Cysts usually contain chylous fluid.

Discussion

Imaging• US: Appears as multilocular, predominately cystic mass with septae. It also has

echogenic areas due to small lymphatics.• CT: Appears as a poorly circumscribed, multiloculated mass. It is typically

hypoattenuating and may have fluid-fluid levels.• MRI: Appears as low intensity on T1. Hyperintense on T2.

Discussion

Cystic hygroma. Koeller K K et al. Radiographics 1999;19:121-146

Thymic Cyst

The thymus and parathyroids arise from the 3rd and 4th pharyngeal pouches. The thymus then descends into the mediastinum through the thymopharyngeal duct, lateral to the thyroid.

These can be found anywhere along the thymopharyngeal duct, and usually occur in the first decade of life.

Clinically present as slow growing, painless mass on lateral neck. They can present from 1 cm-26 cm.

Lined by squamous epithelium with thymic tissue in the cyst wall.

Imaging•US: unilocular cystic mass extending downward parallel to SCM•CT: unilocular or multilocular, hypoattenuating, adjacent to carotid space•MRI: hypointense on T1, hyperintense on T2

Discussion

Thyroglossal duct cyst

Diagnosis

Ahuja AT, Wong KT, King AD, et al. Imaging for thyroglossal duct cyst: the bare essentials. Clinical Radiology 2005;60:141-148.

Brewis C, Mahadevan M, Bailey CM, et al. Investigation and treatment of thyroglossal cysts in children. J R Soc Med 2000;93:18-21.

Koch B. Cystic malformations of the neck in children. Pediatr Radiol 2005;35:463–477.

Koeller K, Alamo L, Adair C, et al. Congenital cystic masses of the neck: radiologic-pathologic correlation. Radiographics 1999 Jan-Feb;19(1):121-46.

Gupta P, Maddalozzo J. Preoperative sonography in presumed thyroglossal duct cysts. Arch Otolaryngol Head Neck Surg 2001;127:200-202.

Lim-Dunham J, Feinstein K, Yousefzadeh D et al. Sonographic demonstration of a normal thyroid gland excludes ectopic thyroid in patients with thyroglossal duct cyst. AJR Am J Roentgenol 1995 June;164(6):1489-91.

References