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Neuroradiology Case of
the Week
Case 186
Scott Cassar, MD,
Ajay Malhotra, MD,
and Per-Lennart Westesson, MD, PhD, DDS
Clinical
Presentation: A 12-year old male with an asymptomatic left neck mass for the past month. CT revealed a well-defined hypodense area in the left anterior mediastinum.
Radiological Findings:There is a relatively well-defined multilobulated cystic lesion in the left lower neck. This lesion lies just inferior to the left lobe of the thyroid gland slightly towards the left of the midline. It is predominantly iso to hypo on T1 and shows a fluid level. This lesion measures approximately 2.6 cm in transverse dimension to approximately 3 cm in superoinferior extent. The inferior extent is at the level of the sternal notch. Post-contrast images do not reveal any obvious soft tissue enhancement. The adjacent fat planes are well preserved. The cystic lesion lies in relation to the superior extent of the thymus which appears normal. There is no significant cervical lymphadenopathy. The third image below shows normal thymus just inferior to the other images.
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| Figure 1:
Thymic cyst T1 |
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| Figure 2: Thymic cyst T2 |
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| Figure 3: Thymic cyst T1 post |
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| Figure 4: CT shows a cystic lesion in the left anterior upper mediastinum. |
Diagnosis: Thymic cyst
Discussion: This multilobulated lesion in the left lower neck with a fluid level in relation to the superior lobe of thymus is a thymic cyst.
Thymic cysts may be congenital or acquired. They contain thin or gelatinous fluid and are characterized histologically by an epithelial lining with thymic tissue in the cyst wall. They are often calcified, resulting in a characteristic radiographic appearance.
Congenital thymic cysts represent an anomaly of pharyngeal pouch formation and are uncommon, accounting for only 1 percent of mediastinal masses. They are believed to develop from remnants of thymic tissue that have failed to descend from the ventral wing of the third branchial pouch into the mediastinum during the 6th to 8th week of fetal life. Most cases in the neck are asymptomatic and usually appear incidentally between ages 6 and 8 years as a soft swelling in the anterior neck triangle rarely invading contiguous structures. Others children may develop respiratory distress, tracheal compression, swelling and enlargement due to hemorrhage or infection. Malignant transformation has also been documented. They may be confused with branchial cleft cysts and cystic hygromas and are treated surgically by complete excision.
Acquired thymic cysts have been associated with previous thoracotomy and concurrent or previously treated Hodgkin’s disease. A biopsy of the lesion should be performed if the clinical and radiographic findings cannot rule out other anterior mediastinal masses such as cystic degeneration of a thymoma, lymphoma, or germ cell neoplasm, which all may appear similar.
References:
- Brant WE, Helms CA. Fundamentals of Diagnostic Radiology, 2nd edition. Philadelphia, Pennsylvania: Lippincott, Williams, & Wilkins; 71-74, 1999.
- Lugo-Vicente HL. Pediatric Surgery Update; 10(4): 2-3, Apr 1998. [Abstract]
- McCafferty MH, Bahnson HT. Thymic cyst extending into the pericardium: a case report and review of thymic cysts. Ann Thorac Surg. 1982 May;33(5):503-6. [Medline]
- Rastegar H, Arger P, Harken AH. Evaluation and therapy of mediastinal thymic cyst. Am Surg. 1980 Apr;46(4):236-8. [Medline]
- Reiner M, Beck AR. Cervical thymic cysts in children. Am J Surg. 1980 May;139(5):704-7. [Medline]
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