Reactive thymic hyperplasia following chemotherapy for children with lymphoma: computed tomography may be able to provide valuable information to avoid over-treatment.

OBJECTIVES

To analyse the clinical and computed tomography (CT) findings related to reactive thymic hyperplasia in order to improve the recognition of this phenomenon and avert over-treatment.

METHODS

Fifty-two children with pathologically proven lymphoma developed reactive thymic hyperplasia following chemotherapy, which was confirmed with long-term review and follow-up. The clinical and CT findings of these 52 children were retrospectively analysed.

RESULTS

The median follow-up period for the whole study group was 32.9 months. Fifty-one children survived free of disease; 23 of these had been with tumour invasion and the remaining 29 without. The median period from complete remission (CR) of the mediastinal lesions to the date of recurrent mediastinal masses was 8.6 months, which was not statistically significantly different from that of 9.5 months from commencement of treatment to the date of newly developed mediastinal masses (P = 0.495). The median maximal diameters of the recurrent and newly developed mediastinal masses were not significantly different (P = 0.091). All of the 52 cases presented with a single mediastinal mass; 42 masses (42/52, 81%) of those showed trapezoidal or triangular shapes and were well-circumscribed; 10 masses (10/52, 19%) manifested diffuse shapes and were ill-circumscribed. Forty-two masses (42/52, 81%) showed homogeneous density. All of the masses revealed mild enhancement after contrast administration. Forty-two masses (42/52, 81%) slightly displaced and 10 masses (10/52, 19%) partly surrounded adjacent vessels. After long-term follow-up, 42 masses (42/52, 81%) shrank naturally, and 10 (10/52, 19%) remained unchanged.

CONCLUSIONS

Reactive thymic hyperplasia can, and often does, occur in children receiving regular chemotherapy for lymphoma, regardless of whether the tumour initially invades the mediastinum. Knowing the characteristic CT findings of this benign entity is helpful in differentiating it from residual or recurrent lymphoma and averting unnecessary treatment.