Reporter: R 陳柏安

Supervisor: Chief 賴炳宏

Date: 2017/12/16

Case Discussion

• Gender: female

• Birth History: 36+5 wks, 2032gm, C/S

• Chief Complain: Sudden found a left neck mass 2 wks after birth. 4x2 cm

Patient Profile

• Cystic lesion within fluid-fluid level

US

• z

MRI

• z

MRI

MRI

• Enhanced smooth thin-walled, cystic unilocular mass with fluid-fluid level

• Hypointensity on T1WI • Mixed hyperintensity on T2WI • Extension to supraclavicular fossa and left

retrophayngeal area • About 4.7*3.7*3.1 cm in size • Lateral-posterior displacement of left carotid

artery and jugular vein • Anterior displacement of left thyroid gland

MRI

What is your impression or differential diagnosis?

• A well-defined large lesion over the left neck without local invasion, with cystic straw-colored clear liquid content.

Operative Findings

• Compatible with cervical thymic cyst

• Contains thymic tissue with Hassall corpuscles in the wall

Pathologic Diagnosis

Squamous cell

Thyroid

Parathyroid Hemorrhage

Hassall's corpuscles

Discussion: Cervical Thymic Cyst

• Cystic remnant of thymopharyngeal duct, derivative of 3rd pharyngeal pouch

Etiology

• Failure of obliteration of thymopharyngeal duct

• Thymopharyngeal duct arises from pyriform sinus, descends into mediastinum

• Persistent sequestered remnants may occur from mandible to thoracic inlet

Etiology

• Peak: 2-15 y/o

• Slight male predilection

• represent less than 1% of cystic cervical masses

Epidemiology

• Often asymptomatic

• Gradually enlarging, soft, compressible mid- to lower cervical neck mass

• When large, may cause dysphagia, respiratory distress, or vocal cord paralysis

Clinical presentation

• Unilocular cystic mass

• extending inferiorly within the neck

• paralleling the SCM or as a dumbbell-shaped left cervicothoracic cystic mass

• Almost always found in left side of neck

• adjacent to the carotid sheath any where from the hyoid bone to the anterior mediastinum

• May splay carotid artery and jugular vein

Image Features

• Thin-walled anechoic or hypoechoic lateral neck mass

• Rarely has solid nodules

in wall

US of CTC

• Dumbbell-shaped left cervicothoracic cystic mass highly suggestive of either thymic cyst or lymphatic malformation

• If unilocular lesion with discrete margins, may be thymic cyst or unilocular lymphatic malformation

Image Features

Cystic masses of neck: A pictorial review, Mittal, et al., Indian Journal of Radiology and Imaging, 2012 Nov

• CT: Nonenhancing low-attenuation neck cyst

– Solid components rare (aberrant thymic tissue, lymphoid aggregates, or parathyroid tissue)

Image Features

Cervical Thymic Cyst: A Rare Differential Diagnosis in Lateral Neck Swelling, Hindawi Publishing Corporation Case Reports in Otolaryngology, Volume 2013

• T1: homogeneous hypointense, still could be variable

– Solid: iso SI

• T2: homogeneous high SI

• T1+C: wall and solid nodules may slightly enhanced

MRI of CTC

MRI of CTC

• 2nd BCC: when infrahyoid, anterior to carotid space

• 4th BCC: most common cyst anterior to left thyroid lobe

• Lymphatic malformation: fluid-fluid level common

• Abscess

• Thyroid cyst: intrathyroid

• Extremely rare: cervical bronchogenic cyst

Common DDx

• CTCs: close to the carotid sheath, between the internal jugular vein and the carotid vessels

• BCCs: superficial and lateral to both the internal jugular vein and carotid artery

• Lymphangiomas: generally restricted to the posterior triangle of the neck

Common DDx

Thymopharyngeal Duct Cyst An Unusual Variant of Cervical Thymic Anomalies, jamaotolaryngology, 2001 Nov.

• lobulated lymphoid tissue containing Hassall’s corpuscles

Pathological Diagnosis

• Excellent prognosis if completely resected

• Recurrence common if incompletely resected

Prognosis

• Often asymptomatic

• Unilocular cystic mass

• Paralleling the SCM

• Most left side

• Dumbbell-shaped

• Could accompanied with bleeding

• DDx: 2nd BCC, Lymphangiomas, and cervical bronchogenic cyst (rare)

Summary

1. Diagnostic Imaging Head and Neck 2E 2. Cystic masses of neck: A pictorial review, Indian J Radiol Imaging. 2012 Oct;22(4):334-43. 3. Diagnosis and Management of Cervical Thymic Cysts in Children, Cureus. 2017 Jan 11;9(1):e973. 4. Cervical thymic cyst: a rare differential diagnosis in lateral neck swelling, Case Rep

Otolaryngol. 2013;2013:350502. 5. Goff CJ et al: Current management of congenital branchial cleft cysts, sinuses, and fistulae. Curr

Opin Otolaryngol Head Neck Surg. 20(6):533-9, 2012 6. Pahlavan S et al: Microbiology of third and fourth branchial pouch cysts. Laryngoscope.

120(3):458-62, 2010 7. Thomas B et al: Revisiting imaging features and the embryologic basis of third and fourth

branchial anomalies. AJNR Am J Neuroradiol. 31(4):755-60, 2010 8. Sturm-O'Brien AK et al: Cervical thymic anomalies--the Texas Children's Hospital experience.

Laryngoscope. 119(10):1988-93, 2009 9. Statham MM et al: Cervical thymic remnants in children. Int J Pediatr Otorhinolaryngol.

72(12):1807-13, 2008 10. Mehrzad H et al: A combined third and fourth branchial arch anomaly: clinical and embryological

implications. Eur Arch Otorhinolaryngol. 264(8):913-6, 2007 11. Charous DD et al: A third branchial pouch cyst presenting as a lateral neck mass in an adult. Ear

Nose Throat J. 85(11):754-7, 2006 12. Koch BL: Cystic malformations of the neck in children. Pediatr Radiol. 35(5):463-77, 2005

Reference

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