Patient population: 20 HIV-positive children (infected perinatally) with moderate to advanced HIV disease with mean age around 10 years
Parameters:
(1) transverse diameter of thymic gland in cm in axial MRI images
(2) antero-posterior (AP) diameter in cm in sagittal MRI images
(3) cranio-caudal (CC) diameter in cm in sagittal MRI images
thymic volume in mL =
= PI() / 6 * (transverse diameter) * (AP diameter) * (CC diameter)
Median thymic volume for patients (not normals) = 10.39 mL
Interpretation:
• A child with a large thymus (greater than the median, 10.39) at initiation of HAART had better long-term immune reconstitution.
• A child with a small thymus (less than the median, 10.39) at initiation of HAART had poorer long-term immune reconstitution.
• According to Ludwig J (Current Methods of Autopsy Practice, 1979) the mean weight of a thymus is 25 grams from 6 to 25 years of age). This suggests some degree of thymic hypoplasia in the study population, with its severity correlating with the response.
Limitations:
• The number of subjects was relatively small.
• The study was done in Italian children and the median volume might vary in a different population.
• The mean weight of the thymus appears to be relatively stable in pediatric patients after infancy. Still it might be necessary to adjust for age and body weight in a given population.
• The thymus is not a uniform organ and tends to fold over mediastinal structures, which might make measurements subject to observer error unless they are standardized.
