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F-18 FDG PET/CT Study Showing Cervical Extension of Thymic Tissue

Wong, Ka Kit, MBBS*; Foster, Elisa, MD; Piert, Morand, MD*

doi: 10.1097/RLU.0b013e31817dec53
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Thymic hyperplasia with increased F-18 fluoro-deoxyglucose (FDG) uptake on PET imaging is a common finding in young children and adolescents after chemotherapy. A variant where thymic tissue extends into the superior mediastinum and lower neck likely represents an embryologic remnant along the track of descent. We report a case of a 4-year-old boy with intracranial sarcoma treated with surgical resection and chemotherapy. An F-18 FDG PET/CT study performed 3 months later revealed anterior mediastinal FDG uptake typical for thymic hyperplasia. Additionally, mild focal uptake in the left lower neck localized to a 1.2-cm soft tissue mass was initially thought to be a lymph node. Review of a head and neck MRI from 10 days earlier demonstrated this mass to be a lobulated extension of thymic tissue into the left medial supraclavicular region. For suspected cases of aberrant cervical thymic tissue, if an anterior neck mass is directly contiguous with and follows the same signal characteristics as the main body of the thymus on MRI, the diagnosis can be confidently made and unnecessary biopsy avoided.

From the Departments of *Radiology/Nuclear Medicine; and †Pediatric Radiology University of Michigan, Ann Arbor, Michigan.

Received for publication October 25, 2007; revision accepted January 17, 2008.

Reprints: Ka Kit Wong, MBBS, Department of Radiology/Nuclear Medicine, University of Michigan Medical Center, B1G 505G University Hospital, 1500 E. Medical Center Drive, Ann Arbor, MI, 48109-0028. E-mail: kakitw@hotmail.com.

© 2008 Lippincott Williams & Wilkins, Inc.