Pediatric residents and their attending pediatrician were discussing a new adolescent oncology patient admission. The teen was diagnosed with lymphoma after presenting with cough, fever and fatigue, and who had mediastinal lymphadenopathy. The attending remarked that lymphoma was common in this age group and also a common cause of anterior mediastinal tumors. “Remember your 4T’s, but thymoma is rare,” he said. “Then why do we always talk about it so much?” asked one of the residents. “I think that’s funny too. Thymoma is rare in kids, but more common in adults. I always think about tumors starting with what is the likely organ it is arising from, then what organs are around in that space like the mediastinum, lungs, abdomen etc. Then what else commonly would metastasize to this area, and then of course, there is always bones and soft tissues that can have tumors arise from them like sarcomas or lipomas or hemangiomas. In this case, the thymus is one of those organs in the area and therefore you have to think about it as a potential cause. Oh, I should also throw in, remember to include infections like tuberculosis or fungal infections infiltrating into tissues which can look like masses, or even diseases like sarcoid. Less common, but like thymomas you should think about potential causes, although we start to work up more likely causes first just because they occur more often. Rare diseases happen rarely but do happen. In this patient’s case, he has mediastinal adenopathy, but also other nodes that we were able to more easily biopsy and therefore make the lymphoma diagnosis,” he discussed.

Figure 149 shows Hodgkin Lymphoma
Discussion
Thymomas are rare pediatric tumors. They can present at all ages from infancy to > 90 years but most occur in the 4th to 5th decades with 10% of thymomas diagnosed in those in the pediatric age range. There are approximately 80 cases of pediatric thymomas in the literature based on a 2022 comprehensive literature review spanning 1985-2020. In this and a 2014 review, males are more commonly affected than females in the pediatric age range, but in adults the genders are about the same percentage or have a slight female predominance.
Thymomas are associated with paraneoplastic processes including presentation with myasthenia gravis. Of pediatric patients with thymomas, 5-15% have been reported as having myasthenia gravis. For adult patients with a thymoma, 30% will develop myasthenia gravis. For those adult patients presenting with myasthenia gravis, 10% will have a thymoma. Overall most thymomas are generally indolent and often present for workup of another condition. However mass effect in the chest (e.g. cough, dyspnea, superior vena cava syndrome) can be a presentation especially in small children.
Learning Point
Thymic tumors include:
Anterior mediastinal tumors are usually remembered by the 4T’s of thymoma, teratoma, thyroid and “terrible” lymphoma. Germ cell tumors and lymphomas are most common. The differential diagnosis includes:
- Germ cell tumors such as teratomas and a variety of benign and malignant tumors of different cell types
- Lymphoma – Hodgkin’s lymphoma is most common.
- Thymic neoplasms – 15% with thymoma being the most common (about 4% of pediatric mediastinal tumors).
- Aberrant thyroid tissue and goiter
- Parathyroid adenoma
- Hemangioma
- Lipomas
- Sarcomas
Questions for Further Discussion
1. Explain the function of the thymus?
2. What is the name of the radiologic sign which shows the thymus on an infant chest radiograph?
3. What are the different types of myasthenia gravis? A review can be found here.
4. Describe the mediastinal spaces? A review can be found here.
5. What are the most common pediatric tumors? A review can be found here.
Related Cases
- Disease: Lymphoma | Thymus Cancer
- Symptom/Presentation: Cough | Fatigue | Fever and Fever of Unknown Origin | Mass or Swelling
- Specialty: Oncology
- Age: Teenager
To view pediatric review articles on this topic from the past year check PubMed.
Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.
Information prescriptions for patients can be found at MedlinePlus for these topics: Lymphoma, Thymus Cancer, and Myasthenia Gravis.
To view current news articles on this topic check Google News.
To view images related to this topic check Google Images.
To view videos related to this topic check YouTube Videos.
Yalcin B, Demir HA, Ciftci AO, et al. Thymomas in Childhood: 11 Cases From a Single Institution. Journal of Pediatric Hematology/Oncology. 2012;34(8):601-605. doi:10.1097/MPH.0b013e31825808e9
Fonseca AL, Ozgediz DE, Christison-Lagay ER, Detterbeck FC, Caty MG. Pediatric thymomas: report of two cases and comprehensive review of the literature. Pediatr Surg Int. 2014;30(3):275-286. doi:10.1007/s00383-013-3438-x
Rossi C, Zanelli M, Sanguedolce F, et al. Pediatric Thymoma: A Review and Update of the Literature. Diagnostics (Basel). 2022;12(9):2205. doi:10.3390/diagnostics12092205
Myasthenia gravis and congenital myasthenic syndromes. In: Handbook of Clinical Neurology. Vol 195. Elsevier; 2023:635-652. doi:10.1016/B978-0-323-98818-6.00010-8
Author
Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa

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