Thymic ultrasound I. Intrathymic anatomy in infants

Background. The gross appearance and echogenicity of the normal thymus have been described, but specific intrathymic anatomy has not been evaluated wi th imaging. Subjects and methods. The thymus from a 34-week-gestation stillborn male wa s examined with ultrasound, and the images were correlated with microscopic findings. Thymic ultrasound was performed in 12 infants without any eviden ce of thymic abnormality, severe infection, or chronic illness. Images were evaluated focusing on intrathymic parenchymal anatomy and compared to the liver, spleen, and thyroid gland. Results. In the specimen thymus, ultrasound demonstrated connective-tissue septa as echogenic linear structures. The cortex was relatively hypoechoic, whereas the medulla was echogenic. The blood vessels within the septa were seen as discrete echoes. In vivo ultrasound demonstrated multiple branchin g echogenic linear structures and foci throughout the parenchyma, represent ing connective-tissue septa or blood vessels within the septa. The normal t hymus was easily differentiated from the liver, spleen, and thyroid glands. Conclusion. Ultrasound is capable of demonstrating intrathymic anatomy, inc luding the medulla, cortex, septa, and blood vessels in a fresh specimen. I n vivo connective-tissue septa and blood vessels in the thymic parenchyma p roduce a unique echo pattern.