Watchful waiting for some children with a mediastinal mass: the potential role for 18 F-fluorodeoxyglucose positron emission tomography: a case report and review of the literature

Abstract

BackgroundBenign hyperplastic thymus is a rare but important differential diagnosis of anterior mediastinal lesions. Histological and radiological criteria are used to distinguish this benign condition from other malignant diseases but have their limitations, and biopsy of mediastinal masses can be risky. We report for the first time the diagnostic value of fluorodeoxyglucose 18 F positron emission tomography for patients with incidentally identified anterior mediastinal masses to avoid biopsy in some cases.Case presentationA 2 year old girl presented with new onset of emesis and constipation leading to the incidental discovery of an anterior mediastinal mass on radiograph. Chest computed tomography revealed cystic components within the mass concerning for a malignancy. Biopsy of the lesion and bone marrow aspiration and biopsy were negative but there was concern that the mediastinal biopsy may have missed the malignant component of the lesion. Hence, a positron emission tomography scan was obtained that showed mild homogeneous fluorodeoxyglucose 18 F avidity within the mass similar to that of normal thymus. The diagnosis of benign hyperplastic thymus was made.ConclusionThe differential diagnosis of an incidentally found anterior mediastinal mass includes malignancy, but benign lesions such as benign hyperplastic thymus must also be considered, particularly when the complete blood count and biochemical profile are normal. Fluorodeoxyglucose 18 F positron emission tomography can help guide a clinician’s decision for further interventions and treatment.

Massive thymic hyperplasia in a 15‐month‐old boy: Case report and literature review

“…Chemical shift magnetic resonance imaging is reported to be helpful in differentiating thymic lymphoid hyperplasia from thymic neoplasm, but it is not always enough . Therefore, separating these entities requires fine‐needle aspiration or biopsy …”

“…As there are no generally accepted criteria for defining “massive,” in literature, the following guidelines are suggested: (a) the thymus should be greater than the heart shadow on posterior‐anterior chest radiograph, (b) it should weigh several times the expected weight for the age of the patient, and (c) it should represent more than 2% of the body mass . About 50 cases of MTH have been recorded . The majority of cases occur between 1 and 15 years, rarely later…”

“…Furthermore, there are no clear indications regarding duration and dosage of the corticosteroid. A small number of patients were reported to be treated conservatively, mostly for incidental findings, or in children with few symptoms and with no acute complications . In fact, the rate of atrophy of an MTH is often very slow and it could potentially lead to complications such as acute airway obstruction .…”

“…7 It must be differentiated from other anterior mediastinal masses (including thymic lymphoma, thymoma, and germ cell tumors) and from other causes of thymus enlargement (thymus lymphofollicular hyperplasia typical of myasthenia gravis 3,8,9 or thymus enlargement after treatment for malignant tumors, stress, and steroid therapy). 1,[5][6][7]10 Clinical and instrumental diagnosis is difficult. Chemical shift magnetic resonance imaging is reported to be helpful in differentiating thymic lymphoid hyperplasia from thymic neoplasm, but it is not always enough.…”

“…11 Therefore, separating these entities requires fineneedle aspiration or biopsy. [1][2][3][4][5]10 Massive true thymic hyperplasia (MTH) is a variant of TTH. As there are no generally accepted criteria for defining "massive," in literature, the following guidelines are suggested: (a) the thymus should be greater than the heart shadow on posterior-anterior chest radiograph, (b) it should weigh several times the expected weight for the age of the patient, and (c) it should represent more than 2% of the body mass.…”