Rebound enlargement of an ectopic cervical thymus mimicking relapse of lymphoblastic lymphoma

Excerpt

A previously healthy 6-year-old boy was referred to our hospital with a tumor in the right upper mediastinum on chest X-ray. Physical examination showed no abnormal respiratory sounds, hepatosplenomegaly, or palpable tumor. On MRI, a right mediastinal tumor, 37 × 38 × 25 mm in size, with low intensity on T1-weighted images and high intensity on T2-weighted images was seen. A left-sided cervical mass, 27 × 29 × 10 mm in size, and several small lesions were seen in the liver and kidneys; all were of intensities similar to those of the mediastinal tumor (Fig. 1a, b). On histopathological examination of the biopsied samples from the mediastinal tumor, diffuse proliferation of medium-sized atypical lymphocytes with scant cytoplasm and fine chromatin was seen (Fig. 2); immunohistochemistry was positive for CD79a, CD10, and CD34, and negative for CD3, CD7, and CD20. Bone marrow aspiration showed a normocellular marrow with 5.4% lymphoblasts, suggesting involvement of lymphoma cells. These findings led to a diagnosis of precursor B-cell lymphoblastic lymphoma (LBL) stage IV.

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