Superior cervical extension of the thymus: a normal finding that should not be mistaken for a mass

To determine the proportion of children and young adults in whom the thymus extends superiorly above the level of the manubrium into the anterior cervical tissues on magnetic resonance (MR) imaging studies.

This retrospective study was approved by the institutional review board, and written consent was waived. Sagittal proton density-weighted images from MR imaging examinations of the neck and upper chest were obtained for various indications in 200 consecutive patients (121 male and 79 female; mean age, 9.0 years; interquartile range, 5.2-14.2). Images were retrospectively reviewed for frequency of superior extension of the thymus above the manubrium into the lower neck. When present, the greatest sagittal distance of the cervical extension was measured. Associated deformity of the trachea or great vessels was recorded as absent or present. The association between frequency of cervical extension and age group and sex was evaluated for statistically significant correlation by using chi(2) tests and multiple logistic regression.

One hundred thirty-three (66.5%) patients had superior cervical extension of the thymus. The mean distance of the extension above the manubrium was 20.1 mm +/- 6.76 (standard deviation). There was a statistically significant relationship between younger age groups and higher frequency of cervical extension of the thymus (P < .0001). Sex was not a statistically significant factor (P = .1645). No tracheal or vascular deformity was seen in any patient.

Superior cervical extension of the thymus above the manubrium into the lower neck is normal anatomy in children and young adults. This finding should not be misinterpreted as a pathologic mass.