Quiz Page January 2009: Retrocardiac Mass Identified at Birth

What do you see on the chest and abdomen CT? 

The left kidney is located in the thoracic cavity behind the heart. Renal vessels arise from the abdomen. No defect is seen in the diaphragm, and herniation of gastrointestinal organs is not apparent.

What is the pathogenesis of the retrocardiac location of this mass? 

Although the cause of an intrathoracic kidney is uncertain, several mechanisms have been proposed. The previous assumption that maldevelopment of the pleuroperitoneal membrane results in a Bochdalek defect in the diaphragm and diaphragmatic herniation of the kidney1 is no longer accepted after Donat and Donat2 found the incidence of an intrathoracic kidney with a Bochdalek hernia to be less than 0.25%. Alternatively, delayed ingrowth of the ureter into the metanephros may result in a diminished stimulus of the metanephrogenic tissue and a subsequent delay in its differentiation that leads to prolongation of the kidney's ascent.2

However, in this patient, both kidneys lay in the normal position at week 33 of gestation, and the possibility of an exaggerated renal ascent is less likely. Moreover, the renal vessels arise from a normal level. Because the kidneys ascend from the pelvis to the abdomen, they receive their blood supply from the vessels closest to them. In most cases, intrathoracic kidneys have a high origination of the renal vessels.2 It thus seems in our patient that malposition of the kidney might not be related to an exaggerated renal ascent. Hertz and Shahin3 postulated that abnormal high ascent of the embryonic kidney results in its contact with the diaphragm. Development of the diaphragm is affected by contact with the kidney, and a “weakened” diaphragm is disrupted by this contact. In our patient, the prenatal left adrenal mass might have the same role as a highly positioned kidney, ie, direct contact of the mass with the diaphragm, resulting in damage to the diaphragm that then allowed the kidney to rise into the thoracic cavity. The most common differential diagnoses of a prenatal adrenal mass are adrenal hemorrhage and congenital neuroblastoma, and both can regress spontaneously. Unlike maldeveloped diaphragm, injured diaphragm can undergo repair. Furthermore, spontaneous regression of the adrenal mass afterward might result in the intrathoracic kidney as the sole abnormality. At the age of 6 months, the boy was growing well, with normal blood pressure.