Rebound thymic hyperplasia after bone marrow transplantation in children with haemato-oncological diseases

Aim of the study
To evaluate prevalence of rebound thymic hyperplasia (RTH) after bone marrow transplantation (BMT) in paediatric patients with haemato-oncological diseases.

Material and methods
Between February 2013 and December 2017, BMT was performed in 189 paediatric patients with haemato-oncological diseases in our institution. Fifty-six patients who underwent at least two chest computed tomography (CT) exams performed before and after BMT were included in the study. Maximum transverse and anterior-posterior (AP) diameters and CT attenuation of the thymus were measured on axial images. Thymic enlargement was considered when both transverse and AP diameters increased. RTH was defined as the presence of thymic enlargement on CT after BMT relative to the CT taken before.

Results
Twenty of 56 patients (36%) demonstrated RTH (12 boys, 8 girls; age range = 4-18 years; median age = 9.8 years). In 20 patients with RTH, seven patients (35%) were diagnosed with ALL, five patients (25%) with thalassemia, two patients (10%) with AML, and one patient (5%) with various diseases. Mean follow-up period between pre-BMT CT and BMT was 46 days, which was 239 days between BMT and post-BMT CT. Mean thymic transverse and AP diameters were 9 mm and 16 mm, respectively, before BMT, which were 17 mm and 33 mm after BMT. Mean HU was 57 on contrast enhanced and 35 on unenhanced images before BMT, which were 59 and 36, respectively, after BMT.

Conclusions
RTH is common finding after BMT in children with various haemato-oncological diseases and should be taken under consideration in paediatric patients after BMT.