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Asahikawa Medical College Asahikawa 078-8510, Japan
Asahikawa Medical College Asahikawa 078-8510, Japan University of
Iowa College of Medicine Iowa City, IA 52242-1077
Asahikawa Medical College Asahikawa 078-8510, Japan
Thymoma is one of the most common tumors in the anterior mediastinum. However, because the thymus originates in the third branchial pouch and descends into the anterior mediastinum, thymoma can occur in ectopic thymic tissue anywhere along this pathway [1, 2]. To our knowledge, no literature has been published describing MRI findings of cervical thymoma. We present a case of cervical thymoma in which MRI contributed to the diagnosis.
A 35-year-old woman presented with a palpable mass in the left side of her neck. She had noticed swelling in her neck 10 years earlier.
On T1-weighted imaging, the tumor was isointense to skeletal muscle (Fig. 3A). On T2-weighted imaging, it had a slightly higher signal intensity than muscle and a lobulated internal architecture separated by linear areas of low signal intensity (Fig. 3B). Sagittal equilibrium-phase gadolinium-enhanced T1-weighted images also depicted a lobulated internal architecture separated by enhanced linear structures and displaying a sharp border separated by fat planes at the boundary with the thyroid gland (Fig. 3C).
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Surgical exploration was performed and a tumor measuring 7.5 x 4.5 x 4 cm was resected. Pathologically, it proved to be a benign thymoma that was composed of both epithelial cells and lymphocytes. The linear structures intersecting the lobulated architecture of the tumor on MRI corresponded to internal fibrous septa (Fig. 3D). The patient has had an uneventful postoperative course for 1 year.
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Cervical thymoma occurs more commonly in females than in males, at a ratio of 7:1; this ratio is quite different from that of patients with mediastinal thymoma. Patients with cervical thymoma range in age from 11 to 71 years, with an average age of 42.7 years [3]. Most cases occur near the thyroid gland and are misdiagnosed as thyroid masses [3, 4]. Myasthenic symptoms are rare, occurring in only a few cases [2, 3].
T2-weighted and contrast-enhanced T1-weighted images of our patient revealed internal linear structures that corresponded to fibrous septa in the histopathologic specimens. Internal fibrous septa are one of the most characteristic pathologic features of thymoma [1]. Moreover, sagittal MRI may be useful for evaluating the relationship of the mass to the thyroid; fat planes between them may indicate an extrathyroidal origin.
Differential diagnoses for cervical thymoma are a thyroid mass (e.g., goiter, adenoma, thyroid cancer) and a lymphomatous or metastatic mass at the thoracic inlet.
Although imaging features of cervical thymoma resemble those of mediastinal thymoma, preoperative diagnosis might be difficult because of the unusual location and rarity of a cervical thymoma. However, MRI may facilitate the diagnosis of cervical thymoma by showing its precise relationship to the thyroid gland and by revealing the internal fibrous septa of the tumor.
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  M. Nishino, S. K. Ashiku, O. N. Kocher, R. L. Thurer, P. M. Boiselle, and H. Hatabu The thymus: a comprehensive review. RadioGraphics, March 1, 2006; 26(2): 335 - 348. [Abstract] [Full Text] [PDF]
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